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Sample records for astigmatism

  1. Astigmatism

    MedlinePlus

    ... change the shape of the cornea surface to eliminate astigmatism, along with nearsightedness or farsightedness. ... contact lenses. Laser vision correction can most often eliminate, or greatly reduce astigmatism.

  2. Postoperative astigmatism.

    PubMed

    Swinger, C A

    1987-01-01

    With the numerous significant advances in surgical methodology--e.g., microinstrumentation, the operating microscope, the surgical keratometer, and intraocular lenses--that have been developed over the past two decades, both surgeons and patients have become increasingly aware of the final optic result of any surgical intervention. This is especially so since the development of refractive surgery, where good uncorrected vision is frequently the final arbiter of success. We have progressed to the stage where the optic manipulation of the cornea, whether intentional or otherwise, can be understood in terms of a number of variables. These include the preparation and closure of the surgical wound, the choice of suture material, and both intraoperative and postoperative manipulations. Where these have failed and postoperative astigmatism still occurs, a number of surgical procedures are available to reduce the astigmatic error to an acceptable level.

  3. Astigmatism in reflector antennas.

    NASA Technical Reports Server (NTRS)

    Cogdell, J. R.; Davis, J. H.

    1973-01-01

    Astigmatic phase error in large parabolic reflector antennas is discussed. A procedure for focusing an antenna and diagnosing the presence and degree of astigmatism is described. Theoretical analysis is conducted to determine the nature of this error in such antennas.

  4. Keratophakia--postoperative astigmatism.

    PubMed

    Swinger, C A; Troutman, R C; Forman, J S

    1987-01-01

    Forty-nine cases of primary keratophakia and 13 cases of secondary keratophakia were analyzed for postoperative astigmatism. For primary cases, the surgically induced astigmatism was 1.55 D, whereas for secondary cases it was 0.19 D (insignificant). There was a tendency for both procedures to induce against-the-rule astigmatism, and both procedures were found capable of producing irregular astigmatism.

  5. Effects of Induced Astigmatism.

    ERIC Educational Resources Information Center

    Schubert, Delwyn G.; Walton, Howard N.

    1968-01-01

    The relationship of astigmatism to reading and the possible detrimental effects it might have on reading were investigated. The greatest incidence of astigmatism was for the with-the-rule type ranging from .50 to 1.00 diopter. This type of astigmatism was induced in 35 seniors from the Los Angeles College of Optometry by placing cylindrical lenses…

  6. Effects of Induced Astigmatism.

    ERIC Educational Resources Information Center

    Schubert, Delwyn G.; Walton, Howard N.

    1968-01-01

    The relationship of astigmatism to reading and the possible detrimental effects it might have on reading were investigated. The greatest incidence of astigmatism was for the with-the-rule type ranging from .50 to 1.00 diopter. This type of astigmatism was induced in 35 seniors from the Los Angeles College of Optometry by placing cylindrical lenses…

  7. Adaptation to astigmatic blur

    PubMed Central

    Sawides, Lucie; Marcos, Susana; Ravikumar, Sowmya; Thibos, Larry; Bradley, Arthur; Webster, Michael

    2011-01-01

    Adapting to blurred or sharpened images alters the perceived focus of subsequently viewed images. We examined whether these adaptation effects could arise from actual sphero-cylindrical refractive errors, by testing aftereffects in images simulating second-order astigmatism. Image blur was varied from negative (vertical) through isotropic to positive (horizontal) astigmatism while maintaining constant blur strength. A 2AFC staircase was used to estimate the stimulus that appeared isotropically blurred before or after adapting to images with astigmatism. Adaptation to horizontal blur caused isotropically blurred images to appear vertically biased and vice versa, shifting the perceived isotropic point toward the adapting level. Aftereffects were similar for different types of images and showed partial selectivity so that strongest effects generally occurred when testing and adapting images were the same. Further experiments explored whether the adaptation depended more strongly on the blurring or “fuzziness” in the images vs. the apparent “figural” changes introduced by the blur, by comparing how the aftereffects transfer across changes in size or orientation. Our results suggest that strong selective adaptation can occur for different lower order aberrations of the eye and that these may be at least partly driven by the apparent figural changes that blurring introduces into the retinal image. PMID:21047754

  8. Ocular residual astigmatism's effect on high myopic astigmatism LASIK surgery

    PubMed Central

    Teus, M A; Arruabarrena, C; Hernández-Verdejo, J L; Cañones, R; Mikropoulos, D G

    2014-01-01

    Purpose To analyze the effect of ocular residual astigmatism (ORA) on the effectiveness of LASIK for treating high myopic astigmatism. Methods This is an observational, cross-sectional study. We studied 116 consecutive myopic eyes with −3 diopters (D) or more of astigmatism that underwent LASIK surgery. The magnitude of uncorrected residual refractive astigmatism 3 months postoperatively was measured. Results The mean preoperative cylinder was −4.0±0.83 D (range, −7.5 to −3 D) and the mean preoperative ORA was 0.82±0.5 D. The mean residual refractive cylinder 3 months postoperatively was −0.78±0.83 D (range, −3 to 0 D). No correlation was found between ORA and the refractive cylinder 3 months postoperatively (P=0.6). Conclusion In eyes with high myopic astigmatism undergoing LASIK, ORA was not correlated with the residual postoperative cylinder. PMID:24971989

  9. Corneal astigmatism after cataract surgery.

    PubMed

    Dekkers, N W; Buijs, J

    1989-08-01

    206 Consecutive cataract patients were at random divided into three groups according to the way the cataract incision was closed: virgin silk 8-0, interrupted nylon 9-0, and double running nylon 9-0. The nylon, whether interrupted or continuous, yielded in the majority of cases a postoperative astigmatism with the rule, whereas virgin silk caused in nearly all patients a postoperative astigmatism against the rule and therefore behaved like an absorbable suture. Silk is chemically non-absorbable, but in virgin silk a natural worm-produced polymer is still present, which provokes a tissue reaction. Softening of tissue diminishes the tensile strength of the suture. With respect to the postoperative astigmatism, the suture material (nylon or virgin silk) seems a more important factor than the way in which it is used (interrupted or continuous).

  10. Influence of posterior corneal astigmatism on postoperative refractive astigmatism in pseudophakic eyes after cataract surgery.

    PubMed

    Sano, Maki; Hiraoka, Takahiro; Ueno, Yuta; Itagaki, Hideo; Ogami, Tomohiro; Oshika, Tetsuro

    2016-12-01

    To examine the influence of posterior corneal astigmatism on postoperative refractive astigmatism in pseudophakic eyes after cataract surgery. The study enrolled 64 pseudophakic eyes of 50 patients (71.8 ± 9.9 years old, mean ± standard deviation) who had undergone phacoemulsification with non-toric IOL implantation. Refractive astigmatism was measured using an auto ref-keratometer with a 0.01- diopter (D) scale. Two types of corneal astigmatism were calculated using anterior segment optical coherence tomography; keratometric and total corneal astigmatism. Keratometric astigmatism was obtained based on anterior corneal curvature alone and total corneal astigmatism was calculated using both anterior and posterior corneal curvatures. The difference between refractive and corneal astigmatism was computed as the vector difference using 1) refractive and keratometric astigmatism and 2) refractive and total corneal astigmatism. The mean refractive, keratometric, and total corneal astigmatism was 0.92 ± 0.48 D, 0.87 ± 0.44 D, and 0.94 ± 0.46 D, respectively. The difference between refractive and keratometric astigmatism (0.70 ± 0.40 D, mean vector of 0.30 D axis 164°) was significantly larger than the difference between refractive and total corneal astigmatism (0.63 ± 0.38 D, mean vector of 0.12 D axis 137°) (P = .019). The difference between refractive and total corneal astigmatism, calculated using both anterior and posterior corneal curvatures, was significantly smaller than the difference between refractive and keratometric astigmatism using anterior corneal astigmatism alone, implying that the latter overestimates the true postoperative refractive astigmatism and can cause cylindrical inaccuracy after cataract surgery.

  11. Distribution of Posterior Corneal Astigmatism According to Axis Orientation of Anterior Corneal Astigmatism

    PubMed Central

    Miyake, Toshiyuki; Shimizu, Kimiya; Kamiya, Kazutaka

    2015-01-01

    Purpose To investigate the distribution of posterior corneal astigmatism in eyes with with-the-rule (WTR) and against-the-rule (ATR) anterior corneal astigmatism. Methods We retrospectively examined six hundred eight eyes of 608 healthy subjects (275 men and 333 women; mean age ± standard deviation, 55.3 ± 20.2 years). The magnitude and axis orientation of anterior and posterior corneal astigmatism were determined with a rotating Scheimpflug system (Pentacam HR, Oculus) when we divided the subjects into WTR and ATR anterior corneal astigmatism groups. Results The mean magnitudes of anterior and posterior corneal astigmatism were 1.14 ± 0.76 diopters (D), and 0.37 ± 0.19 D, respectively. We found a significant correlation between the magnitudes of anterior and posterior corneal astigmatism (Pearson correlation coefficient r = 0.4739, P<0.001). In the WTR anterior astigmatism group, we found ATR astigmatism of the posterior corneal surface in 402 eyes (96.6%). In the ATR anterior astigmatism group, we found ATR posterior corneal astigmatism in 82 eyes (73.9%). Especially in eyes with ATR anterior corneal astigmatism of 1 D or more and 1.5 D or more, ATR posterior corneal astigmatism was found in 28 eyes (59.6%) and 9 eyes (42.9%), respectively. Conclusions WTR anterior astigmatism and ATR posterior astigmatism were found in approximately 68% and 91% of eyes, respectively. The magnitude and the axis orientation of posterior corneal astigmatism were not constant, especially in eyes having high ATR anterior corneal astigmatism, as is often the case in patients who have undergone toric IOL implantation. PMID:25625283

  12. Distribution of posterior corneal astigmatism according to axis orientation of anterior corneal astigmatism.

    PubMed

    Miyake, Toshiyuki; Shimizu, Kimiya; Kamiya, Kazutaka

    2015-01-01

    To investigate the distribution of posterior corneal astigmatism in eyes with with-the-rule (WTR) and against-the-rule (ATR) anterior corneal astigmatism. We retrospectively examined six hundred eight eyes of 608 healthy subjects (275 men and 333 women; mean age ± standard deviation, 55.3 ± 20.2 years). The magnitude and axis orientation of anterior and posterior corneal astigmatism were determined with a rotating Scheimpflug system (Pentacam HR, Oculus) when we divided the subjects into WTR and ATR anterior corneal astigmatism groups. The mean magnitudes of anterior and posterior corneal astigmatism were 1.14 ± 0.76 diopters (D), and 0.37 ± 0.19 D, respectively. We found a significant correlation between the magnitudes of anterior and posterior corneal astigmatism (Pearson correlation coefficient r = 0.4739, P<0.001). In the WTR anterior astigmatism group, we found ATR astigmatism of the posterior corneal surface in 402 eyes (96.6%). In the ATR anterior astigmatism group, we found ATR posterior corneal astigmatism in 82 eyes (73.9%). Especially in eyes with ATR anterior corneal astigmatism of 1 D or more and 1.5 D or more, ATR posterior corneal astigmatism was found in 28 eyes (59.6%) and 9 eyes (42.9%), respectively. WTR anterior astigmatism and ATR posterior astigmatism were found in approximately 68% and 91% of eyes, respectively. The magnitude and the axis orientation of posterior corneal astigmatism were not constant, especially in eyes having high ATR anterior corneal astigmatism, as is often the case in patients who have undergone toric IOL implantation.

  13. Orbital angular momentum of general astigmatic modes

    SciTech Connect

    Visser, Jorrit; Nienhuis, Gerard

    2004-07-01

    We present an operator method to obtain complete sets of astigmatic Gaussian solutions of the paraxial wave equation. In case of general astigmatism, the astigmatic intensity and phase distribution of the fundamental mode differ in orientation. As a consequence, the fundamental mode has a nonzero orbital angular momentum, which is not due to phase singularities. Analogous to the operator method for the quantum harmonic oscillator, the corresponding astigmatic higher-order modes are obtained by repeated application of raising operators on the fundamental mode. The nature of the higher-order modes is characterized by a point on a sphere, in analogy with the representation of polarization on the Poincare sphere. The north and south poles represent astigmatic Laguerre-Gaussian modes, similar to circular polarization on the Poincare sphere, while astigmatic Hermite-Gaussian modes are associated with points on the equator, analogous to linear polarization. We discuss the propagation properties of the modes and their orbital angular momentum, which depends on the degree of astigmatism and on the location of the point on the sphere.

  14. Radial averages of astigmatic TEM images.

    PubMed

    Fernando, K Vince

    2008-10-01

    The Contrast Transfer Function (CTF) of an image, which modulates images taken from a Transmission Electron Microscope (TEM), is usually determined from the radial average of the power spectrum of the image (Frank, J., Three-dimensional Electron Microscopy of Macromolecular Assemblies, Oxford University Press, Oxford, 2006). The CTF is primarily defined by the defocus. If the defocus estimate is accurate enough then it is possible to demodulate the image, which is popularly known as the CTF correction. However, it is known that the radial average is somewhat attenuated if the image is astigmatic (see Fernando, K.V., Fuller, S.D., 2007. Determination of astigmatism in TEM images. Journal of Structural Biology 157, 189-200) but this distortion due to astigmatism has not been fully studied or understood up to now. We have discovered the exact mathematical relationship between the radial averages of TEM images with and without astigmatism. This relationship is determined by a zeroth order Bessel function of the first kind and hence we can exactly quantify this distortion in the radial averages of signal and power spectra of astigmatic images. The argument to this Bessel function is similar to an aberration function (without the spherical aberration term) except that the defocus parameter is replaced by the differences of the defoci in the major and minor axes of astigmatism. The ill effects due this Bessel function are twofold. Since the zeroth order Bessel function is a decaying oscillatory function, it introduces additional zeros to the radial average and it also attenuates the CTF signal in the radial averages. Using our analysis, it is possible to simulate the effects of astigmatism in radial averages by imposing Bessel functions on idealized radial averages of images which are not astigmatic. We validate our theory using astigmatic TEM images.

  15. Visual Motor and Perceptual Task Performance in Astigmatic Students.

    PubMed

    Harvey, Erin M; Twelker, J Daniel; Miller, Joseph M; Leonard-Green, Tina K; Mohan, Kathleen M; Davis, Amy L; Campus, Irene

    2017-01-01

    Purpose. To determine if spectacle corrected and uncorrected astigmats show reduced performance on visual motor and perceptual tasks. Methods. Third through 8th grade students were assigned to the low refractive error control group (astigmatism < 1.00 D, myopia < 0.75 D, hyperopia < 2.50 D, and anisometropia < 1.50 D) or bilateral astigmatism group (right and left eye ≥ 1.00 D) based on cycloplegic refraction. Students completed the Beery-Buktenica Developmental Test of Visual Motor Integration (VMI) and Visual Perception (VMIp). Astigmats were randomly assigned to testing with/without correction and control group was tested uncorrected. Analyses compared VMI and VMIp scores for corrected and uncorrected astigmats to the control group. Results. The sample included 333 students (control group 170, astigmats tested with correction 75, and astigmats tested uncorrected 88). Mean VMI score in corrected astigmats did not differ from the control group (p = 0.829). Uncorrected astigmats had lower VMI scores than the control group (p = 0.038) and corrected astigmats (p = 0.007). Mean VMIp scores for uncorrected (p = 0.209) and corrected astigmats (p = 0.124) did not differ from the control group. Uncorrected astigmats had lower mean scores than the corrected astigmats (p = 0.003). Conclusions. Uncorrected astigmatism influences visual motor and perceptual task performance. Previously spectacle treated astigmats do not show developmental deficits on visual motor or perceptual tasks when tested with correction.

  16. Visual Motor and Perceptual Task Performance in Astigmatic Students

    PubMed Central

    Twelker, J. Daniel; Miller, Joseph M.; Mohan, Kathleen M.; Campus, Irene

    2017-01-01

    Purpose. To determine if spectacle corrected and uncorrected astigmats show reduced performance on visual motor and perceptual tasks. Methods. Third through 8th grade students were assigned to the low refractive error control group (astigmatism < 1.00 D, myopia < 0.75 D, hyperopia < 2.50 D, and anisometropia < 1.50 D) or bilateral astigmatism group (right and left eye ≥ 1.00 D) based on cycloplegic refraction. Students completed the Beery-Buktenica Developmental Test of Visual Motor Integration (VMI) and Visual Perception (VMIp). Astigmats were randomly assigned to testing with/without correction and control group was tested uncorrected. Analyses compared VMI and VMIp scores for corrected and uncorrected astigmats to the control group. Results. The sample included 333 students (control group 170, astigmats tested with correction 75, and astigmats tested uncorrected 88). Mean VMI score in corrected astigmats did not differ from the control group (p = 0.829). Uncorrected astigmats had lower VMI scores than the control group (p = 0.038) and corrected astigmats (p = 0.007). Mean VMIp scores for uncorrected (p = 0.209) and corrected astigmats (p = 0.124) did not differ from the control group. Uncorrected astigmats had lower mean scores than the corrected astigmats (p = 0.003). Conclusions. Uncorrected astigmatism influences visual motor and perceptual task performance. Previously spectacle treated astigmats do not show developmental deficits on visual motor or perceptual tasks when tested with correction. PMID:28293434

  17. Influence factors of estimation errors for total corneal astigmatism using keratometric astigmatism in patients before cataract surgery.

    PubMed

    Zheng, Tianyu; Chen, Zhanghua; Lu, Yi

    2016-01-01

    To evaluate the influence factors of the estimation errors for total corneal astigmatism using keratometric astigmatism in patients preparing for cataract surgery. EYE and ENT Hospital of Fudan University, Shanghai, China. Prospective observational study. Eyes of patients preparing for cataract surgery were measured with Pentacam Scheimpflug imaging device. Keratometric astigmatism was obtained using the anterior corneal surface measurement and the keratometric index (1.3375) while neglecting the posterior corneal surface measurement. The Scheimpflug-measured total corneal astigmatism was derived by vector analysis of the astigmatism on both corneal surfaces. The study comprised 374 eyes of 374 patients 45 to 84 years old. The mean absolute error in magnitude and mean absolute error in angle comparing keratometric astigmatism with Scheimpflug-derived astigmatism was 0.18 ± 0.14 diopter (D) and 7.7 ± 11.0 degrees, respectively. The mean magnitude of the error vector was 0.24 ± 0.14 D. The error in magnitude was significantly larger in eyes with against-the-rule anterior astigmatism, while error in angle was larger in eyes with with-the-rule and oblique anterior astigmatism. Multiple regressions showed that 4 predictors (difference in anterior-posterior astigmatism axis, magnitude of posterior astigmatism, magnitude of keratometric astigmatism, and axial length [AL]) were significantly associated with the absolute error in magnitude. Predictors including the difference in the anterior-posterior astigmatism axis, magnitude of posterior astigmatism, magnitude of keratometric astigmatism, and age were significantly associated with the absolute error in angle and magnitude of the error vector. Neglecting posterior corneal astigmatism yielded significant estimation errors in total corneal astigmatism in patients preparing for cataract surgery. Estimation errors were significantly influenced by the difference in the anterior -posterior astigmatism axis, magnitude of

  18. A design of PAL with astigmatism

    NASA Astrophysics Data System (ADS)

    Wei, Yefei; Xiang, Huazhong; Zhu, Tianfeng; Chen, Jiabi

    2015-08-01

    Progressive addition lens (PAL) is designed for those who suffer from myopia and presbyopia to have a clear vision from a far distance to a nearby distance. Additionally there are many people that also suffer from astigmatism and need to be corrected. The cylinder power can't be simply added to the diopter of the PAL directly, because the diopter of the PAL needs to be changed smoothly. A methods has been proposed in this article to solve the problem, the freeform surface height of a PAL without astigmatism and the cylindrical lens surface height for the correction of astigmatism are calculated separately. The both two surface heights were added together, then the final surface is produced and shown with the both properties of PALs and cylindrical lenses used to correct the astigmatism.

  19. Perceptual Adaptation to the Correction of Natural Astigmatism

    PubMed Central

    Vinas, Maria; Sawides, Lucie; de Gracia, Pablo; Marcos, Susana

    2012-01-01

    Background The visual system adjusts to changes in the environment, as well as to changes within the observer, adapting continuously to maintain a match between visual coding and visual environment. We evaluated whether the perception of oriented blur is biased by the native astigmatism, and studied the time course of the after-effects following spectacle correction of astigmatism in habitually non-corrected astigmats. Methods and Findings We tested potential shifts of the perceptual judgments of blur orientation in 21 subjects. The psychophysical test consisted on a single interval orientation identification task in order to measure the perceived isotropic point (astigmatism level for which the image did not appear oriented to the subject) from images artificially blurred with constant blur strength (B = 1.5 D), while modifying the orientation of the blur according to the axis of natural astigmatism of the subjects. Measurements were performed after neutral (gray field) adaptation on naked eyes under full correction of low and high order aberrations. Longitudinal measurements (up to 6 months) were performed in three groups of subjects: non-astigmats and corrected and uncorrected astigmats. Uncorrected astigmats were provided with proper astigmatic correction immediately after the first session. Non-astigmats did not show significant bias in their perceived neutral point, while in astigmatic subjects the perceived neutral point was significantly biased, typically towards their axis of natural astigmatism. Previously uncorrected astigmats shifted significantly their perceived neutral point towards more isotropic images shortly (2 hours) after astigmatic correction wear, and, once stabilized, remained constant after 6 months. The shift of the perceived neutral point after correction of astigmatism was highly correlated with the amount of natural astigmatism. Conclusions Non-corrected astigmats appear to be naturally adapted to their astigmatism, and astigmatic

  20. Generalization of Seidel astigmatism and Petzval curvature.

    PubMed

    Gaj, M

    1966-06-01

    In a paper probably to be published in Optika i Spektroskopiya the wave aberration for sagittal focus for the arbitrary surface of rotational symmetry has been carried out on the base of the astigmatic beam invariant D(s) = nu(s)d(s). The resulting expression for the wave aberration has been reformulated into three terms which, in the Seidel region, go over into astigmatism (the first) and into the Petzval curvature (the second) while the third disappears.

  1. Identification of a Candidate Gene for Astigmatism

    PubMed Central

    Lopes, Margarida C.; Hysi, Pirro G.; Verhoeven, Virginie J. M.; Macgregor, Stuart; Hewitt, Alex W.; Montgomery, Grant W.; Cumberland, Phillippa; Vingerling, Johannes R.; Young, Terri L.; van Duijn, Cornelia M.; Oostra, Ben; Uitterlinden, Andre G.; Rahi, Jugnoo S.; Mackey, David A.; Klaver, Caroline C. W.; Andrew, Toby; Hammond, Christopher J.

    2013-01-01

    Purpose. Astigmatism is a common refractive error that reduces vision, where the curvature and refractive power of the cornea in one meridian are less than those of the perpendicular axis. It is a complex trait likely to be influenced by both genetic and environmental factors. Twin studies of astigmatism have found approximately 60% of phenotypic variance is explained by genetic factors. This study aimed to identify susceptibility loci for astigmatism. Methods. We performed a meta-analysis of seven genome-wide association studies that included 22,100 individuals of European descent, where astigmatism was defined as the number of diopters of cylinder prescription, using fixed effect inverse variance-weighted methods. Results. A susceptibility locus was identified with lead single nucleotide polymorphism rs3771395 on chromosome 2p13.3 (meta-analysis, P = 1.97 × 10−7) in the VAX2 gene. VAX2 plays an important role in the development of the dorsoventral axis of the eye. Animal studies have shown a gradient in astigmatism along the vertical plane, with corresponding changes in refraction, particularly in the ventral field. Conclusions. This finding advances the understanding of refractive error, and provides new potential pathways to be evaluated with regard to the development of astigmatism. PMID:23322567

  2. Long-term follow-up of astigmatic keratotomy for corneal astigmatism after penetrating keratoplasty.

    PubMed

    Böhringer, Daniel; Dineva, Nina; Maier, Philip; Birnbaum, Florian; Kirschkamp, Thomas; Reinhard, Thomas; Eberwein, Philipp

    2016-11-01

    To report the long-term stability of paired arcuate corneal keratotomies (AKs) in patients with high regular postpenetrating keratoplasty astigmatism. Retrospective chart review of best-corrected visual acuity, refraction and keratometric values of 41 eyes with AK between 2003 and 2012. Magnitude of median target induced astigmatism vector was 9.2 dioptres (Dpt). We reached a median magnitude of surgically induced astigmatism vector of 9.81 Dpt and a median magnitude of difference vector of 5.5 Dpt. In keratometry, we achieved a net median astigmatism reduction by 3.3 Dpt. The average correction index was 1.14, showing a slight overcorrection. Irregularity of keratometric astigmatism increased by 0.6 Dpt, and spherical equivalent changed by 1.75 Dpt. Monocular best spectacle corrected visual acuity increased from preoperatively 20/63 (0.5 logMAR) to 20/40 (0.3 logMAR) postoperatively. Median gain on the ETDRS chart was two lines. Long-term follow-up showed a median keratometric astigmatic increase by 0.3 Dpt per year. Arcuate corneal keratotomies is a safe and effective method to reduce high regular corneal astigmatism following penetrating keratoplasty but has limited predictability. The long-term follow-up shows an increase of keratometric astigmatism by 0.3 Dpt/year, equalizing the surgical effect after 10 years. © 2016 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

  3. LASIK for spherical refractive myopia: effect of topographic astigmatism (ocular residual astigmatism, ORA) on refractive outcome.

    PubMed

    Frings, Andreas; Richard, Gisbert; Steinberg, Johannes; Skevas, Christos; Druchkiv, Vasyl; Katz, Toam; Linke, Stephan J

    2015-01-01

    In eyes with a preoperative plano refractive cylinder, it would appear that there is no rationale for astigmatic treatment. The aim of this retrospective, cross-sectional data analysis was to determine the amount of topographic astigmatism in refractive plano eyes that results in reduced efficacy after myopic laser in situ keratomileusis (LASIK). This study included 267 eyes from 267 consecutive myopic patients with a refractive plano cylinder. Receiver operating characteristic analysis was used to find the cut-off values of preoperative ocular residual astigmatism (= topographic astigmatism) that can best discriminate between groups of efficacy and safety indices in preoperative plano refractive cylinder eyes. Preoperative ocular residual astigmatism (ORA) (or topographic astigmatism) of ≤0.9 diopters (D) resulted in an efficacy index of at least 0.8 statistically significantly more frequently than eyes with a preoperative ORA of >0.9 D. Eyes with a high ORA preoperatively also had a high ORA postoperatively. Regression analysis showed that each diopter of preoperative ORA reduced efficacy by 0.07. A preoperative corneal astigmatism of ≥0.9 D could (partially) be taken into account in the LASIK design, even if the subjective refractive astigmatism is neutral.

  4. Reading Fluency in School-Age Children with Bilateral Astigmatism

    PubMed Central

    Harvey, Erin M.; Miller, Joseph M.; Twelker, J. Daniel; Davis, Amy L.

    2015-01-01

    Purpose To compare oral reading fluency (ORF) in students with no/low astigmatism and moderate/high astigmatism and to assess the impact of spectacle correction on ORF in moderate and high astigmats. Methods Subjects were 3rd–8th grade students from a highly astigmatic population. Refractive error was determined through subjectively refined cycloplegic autorefraction. Data from students with ocular abnormalities, anisometropia, symptomatic binocular vision disorders, or refractive error that did not meet study criteria (no/low (cyl < 1.00 both eyes, no significant myopia/hyperopia), moderate (cyl ≥ 1.00 D both eyes, mean ≥ 1.00 D and < 3.00 D), or high astigmatism group (cyl ≥ 1.00 D both eyes, mean ≥ 3.00 D)) were excluded. ORF was tested with a modified version of the DIBELS Next test of ORF. No/low astigmats were tested without spectacles; astigmats were tested with and without spectacles. Mean ORF was compared in no/low astigmats and astigmats (with and without correction). Improvement in ORF with spectacles was compared for moderate and high astigmats. Results The sample included 130 no/low, 67 moderate, and 76 high astigmats. ORF was lower in uncorrected astigmats than in no/low astigmats (p=0.011). ORF did not significantly differ in no/low astigmats and corrected astigmats (p=0.10). ORF significantly improved with spectacle correction in high astigmats (p=0.001, mean improvement 6.55 words per minute (WPM)), but not in moderate astigmats (p=0.193, mean improvement 1.87 WPM). Effects of spectacle wear were observed in students who read smaller text stimuli (older grades). Conclusions ORF is significantly reduced in students with bilateral astigmatism (≥ 1.00D) when uncorrected, but not when best-corrected, compared to their non-astigmatic peers. Improvement in ORF with spectacle correction is seen in high astigmats, but not in moderate astigmats. These data support the recommendation for full-time spectacle wear in astigmatic students

  5. Improved astigmatic focus error detection method

    NASA Technical Reports Server (NTRS)

    Bernacki, Bruce E.

    1992-01-01

    All easy-to-implement focus- and track-error detection methods presently used in magneto-optical (MO) disk drives using pre-grooved media suffer from a side effect known as feedthrough. Feedthrough is the unwanted focus error signal (FES) produced when the optical head is seeking a new track, and light refracted from the pre-grooved disk produces an erroneous FES. Some focus and track-error detection methods are more resistant to feedthrough, but tend to be complicated and/or difficult to keep in alignment as a result of environmental insults. The astigmatic focus/push-pull tracking method is an elegant, easy-to-align focus- and track-error detection method. Unfortunately, it is also highly susceptible to feedthrough when astigmatism is present, with the worst effects caused by astigmatism oriented such that the tangential and sagittal foci are at 45 deg to the track direction. This disclosure outlines a method to nearly completely eliminate the worst-case form of feedthrough due to astigmatism oriented 45 deg to the track direction. Feedthrough due to other primary aberrations is not improved, but performance is identical to the unimproved astigmatic method.

  6. Reading Fluency in School-Aged Children with Bilateral Astigmatism.

    PubMed

    Harvey, Erin M; Miller, Joseph M; Twelker, J Daniel; Davis, Amy L

    2016-02-01

    To compare oral reading fluency (ORF) in students with no/low astigmatism and moderate/high astigmatism and to assess the impact of spectacle correction on ORF in moderate and high astigmats. Subjects were third- to eighth-grade students from a highly astigmatic population. Refractive error was determined through subjectively refined cycloplegic autorefraction. Data from students with ocular abnormalities, anisometropia, symptomatic binocular vision disorders, or refractive error that did not meet study criteria (no/low [cylinder < 1.00 both eyes, no significant myopia/hyperopia], moderate [cylinder ≥ 1.00 D both eyes, mean ≥ 1.00 D and < 3.00 D], or high astigmatism group [cylinder ≥ 1.00 D both eyes, mean ≥ 3.00 D]) were excluded. Oral reading fluency was tested with a modified version of the Dynamic Indicators of Basic Early Literacy Skills (DIBELS) Next test of ORF. No/low astigmats were tested without spectacles; astigmats were tested with and without spectacles. Mean ORF was compared in no/low astigmats and astigmats (with and without correction). Improvement in ORF with spectacles was compared between moderate and high astigmats. The sample included 130 no/low, 67 moderate, and 76 high astigmats. ORF was lower in uncorrected astigmats than in no/low astigmats (p = 0.011). ORF did not significantly differ in no/low astigmats and corrected astigmats (p = 0.10). ORF significantly improved with spectacle correction in high astigmats (p = 0.001; mean improvement, 6.55 words per minute) but not in moderate astigmats (p = 0.193; mean improvement, 1.87 words per minute). Effects of spectacle wear were observed in students who read smaller text stimuli (older grades). ORF is significantly reduced in students with bilateral astigmatism (≥1.00D) when uncorrected but not when best-corrected compared with their nonastigmatic peers. Improvement in ORF with spectacle correction is seen in high astigmats but not in moderate astigmats. These data support the

  7. Influence of Posterior Corneal Astigmatism on Total Corneal Astigmatism in Eyes With Keratoconus.

    PubMed

    Savini, Giacomo; Næser, Kristian; Schiano-Lomoriello, Domenico; Mularoni, Alessandro

    2016-11-01

    To measure posterior corneal astigmatism (PCA) and investigate its influence on total corneal astigmatism (TCA) in eyes with keratoconus. Keratometric astigmatism (KA), PCA, and TCA were investigated by means of a dual Scheimpflug analyzer in patients with keratoconus. Vector analysis was carried out with the Næser polar value method. We enrolled 119 eyes. PCA magnitude averaged 0.77 ± 0.43 diopters (D) and exceeded 0.50, 1.00, and 2.00 D in 73.9%, 21.8%, and 16.8% of eyes, respectively. PCA averaged 0.95 ± 0.48, 0.55 ± 0.28, and 0.70 ± 0.35 D in eyes with with-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism. The steepest posterior meridian was oriented vertically (between 61 and 119 degrees) in 55.5% of eyes, thus generating ATR astigmatism. The difference between the location of the steepest meridian of KA and that of TCA was >10 degrees in 8.4% of eyes. On average, KA overestimated TCA in eyes with WTR astigmatism by 0.16 D and underestimated TCA in eyes with ATR astigmatism by 0.22 D. The PCA power oriented along the steeper anterior corneal meridian averaged -0.83 ± 0.40, -0.40 ± 0.37, and -0.53 ± 0.43 D for WTR, ATR, and obliquely astigmatic eyes, respectively. Linear regression disclosed a statistically significant correlation (P < 0.0001, r = 0.16) between the meridional powers of TCA and PCA. In eyes with keratoconus, PCA displays large, variable values and is correlated to TCA. The influence of PCA on TCA cannot be disregarded when planning astigmatism correction by toric intraocular lenses.

  8. Surgical correction of astigmatism during cataract surgery.

    PubMed

    Buckhurst, Phillip J; Wolffsohn, James S; Davies, Leon N; Naroo, Shehzad A

    2010-11-01

    High levels of corneal astigmatism are prevalent in a significant proportion of the population. During cataract surgery pre-existing astigmatism can be corrected using single or paired incisions on the steep axis of the cornea, using relaxing incisions or with the use of a toric intraocular lens. This review provides an overview of the conventional methods of astigmatic correction during cataract surgery and in particular, discusses the various types of toric lenses presently available and the techniques used in determining the correct axis for the placement of such lenses. Furthermore, the potential causes of rotation in toric lenses are identified, along with techniques for assessing and quantifying the amount of rotation and subsequent management options for addressing post-operative rotation.

  9. Spherical aberrations of human astigmatic corneas.

    PubMed

    Zhao, Huawei; Dai, Guang-Ming; Chen, Li; Weeber, Henk A; Piers, Patricia A

    2011-11-01

    To evaluate whether the average spherical aberration of human astigmatic corneas is statistically equivalent to human nonastigmatic corneas. Spherical aberrations of 445 astigmatic corneas prior to laser vision correction were retrospectively investigated to determine Zernike coefficients for central corneal areas 6 mm in diameter using CTView (Sarver and Associates). Data were divided into groups according to cylinder power (0.01 to 0.25 diopters [D], 0.26 to 0.75 D, 0.76 to 1.06 D, 1.07 to 1.53 D, 1.54 to 2.00 D, and >2.00 D) and according to age by decade. Spherical aberrations were correlated with age and astigmatic power among groups and the entire population. Statistical analyses were conducted, and P<.05 was considered statistically significant. Mean patient age was 42.6±11 years. Astigmatic corneas had an average astigmatic power of 0.78±0.58 D and mean spherical aberration was 0.25±0.13 μm for the entire population and approximately the same (0.27 μm) for individual groups, ranging from 0.23 to 0.29 μm (P>.05 for all tested groups). Mean spherical aberration of astigmatic corneas was not correlated significantly with cylinder power or age (P>.05). Spherical aberrations are similar to those of nonastigmatic corneas, permitting the use of these additional data in the design of aspheric toric intra-ocular lenses. Copyright 2011, SLACK Incorporated.

  10. [Essential features of astigmatism and its correction with excimer laser].

    PubMed

    Vlaicu, Valeria

    2012-01-01

    The correction of astigmatism is an essential element for the refractive surgery because the majority of patients have important preoperative cylinder An uncorrected astigmatism decreases visual acuity and can also cause glare, asthenopia, headaches, monocular diplopia. It is important to remark that a complete elimination of astigmatism for the eye is very rarely achieved.

  11. Comparison of astigmatic correction after femtosecond lenticule extraction and small-incision lenticule extraction for myopic astigmatism.

    PubMed

    Kobashi, Hidenaga; Kamiya, Kazutaka; Ali, Mohamed A; Igarashi, Akihito; Elewa, Mohamed Ehab M; Shimizu, Kimiya

    2015-01-01

    To compare postoperative astigmatic correction between femtosecond lenticule extraction (FLEx) and small-incision lenticule extraction (SMILE) in eyes with myopic astigmatism. We examined 26 eyes of 26 patients undergoing FLEx and 26 eyes of 26 patients undergoing SMILE to correct myopic astigmatism (manifest astigmatism of 1 diopter (D) or more). Visual acuity, cylindrical refraction, the predictability of the astigmatic correction, and the astigmatic vector components using Alpin's method, were compared between the two groups 3 months postoperatively. We found no statistically significant difference in manifest cylindrical refraction (p=0.74) or in the percentage of eyes within ± 0.50 D of their refraction (p=0.47) after the two surgical procedures. Moreover, no statistically significant difference was detected between the groups in astigmatic vector components, namely, surgically induced astigmatism (0.80), target induced astigmatism (p=0.87), astigmatic correction index (p=0.77), angle of error (p=0.24), difference vector (p=0.76), index of success (p=0.91), flattening effect (p=0.79), and flattening index (p=0.84). Both FLEx and SMILE procedures are essentially equivalent in correcting myopic astigmatism using vector analysis, suggesting that the lifting or non-lifting of the flap does not significantly affect astigmatic outcomes after these surgical procedures.

  12. Correlation of major components of ocular astigmatism in myopic patients.

    PubMed

    Mohammadpour, Mehrdad; Heidari, Zahra; Khabazkhoob, Mehdi; Amouzegar, Afsaneh; Hashemi, Hassan

    2016-02-01

    To investigate the correlation of major components of ocular astigmatism in myopic patients in an academic hospital. This cross-sectional study was conducted on 376 eyes of 188 patients who were referred to Farabi Eye Hospital for refractive surgery. Preoperative examinations including refraction and corneal topography were performed for all candidates to measure refractive and corneal astigmatism. Ocular residual astigmatism was calculated using vector analysis. Pearson's correlation and ANOVA analysis were used to evaluate the strength of the association between different types of astigmatism. Both eyes were defined as cluster and the Generalized Estimating Equations (GEE) analysis were performed. Mean age of 119 women (63.3%) and 69 men (36.7%) was 27.8 ± 5.7 years. Mean refractive error based on spherical equivalent was -3.59 ± 1.95D (range, -0.54 to -10.22D). Mean refractive and corneal astigmatism was 1.97 ± 1.3D and 1.85 ± 1.01D, respectively. Mean amount of ORA was 0.65 ± 0.36D.There was a significant correlation between ORA and refractive astigmatism(r=0.23, p<0.001), corneal and refractive astigmatism (r=0.91, p<0.001) and a weak correlation between ORA and corneal astigmatism (r=0.13, p=0.014). There was a significant correlation between J0 and J45 values of ORA and corneal astigmatism (p<0.001). There is a significant correlation between ORA and refractive astigmatism, refractive and corneal astigmatism and a weak correlation between ORA and corneal astigmatism in refractive surgery candidates. Identifying the type of astigmatism and preoperative measurement of ocular residual astigmatism is highly recommended prior to any refractive surgery, especially in cases with significant astigmatism. Copyright © 2015 Elsevier Ltd. All rights reserved.

  13. Astigmatism transfer phenomena in the optical parametric amplification process

    NASA Astrophysics Data System (ADS)

    Li, Wenkai; Chen, Yun; Li, Yanyan; Xu, Yi; Guo, Xiaoyang; Lu, Jun; Leng, Yuxin

    2017-01-01

    We numerically and experimentally investigate the astigmatism transfer phenomena in femtosecond optical parametric amplification (OPA). We model the OPA process based on the coupled second-order three-wave nonlinear propagation equations. The numerical and experimental results support that the input pump pulse astigmatism can be transferred into the idler pulse but not the signal pulse, and the idler pulse astigmatism originating from spatial walk-off is less than the idler pulse astigmatism received from the pump. Thus, we can provide a clear understanding of astigmatism transfer mechanisms in the OPA process, and make better use of broadband tunable OPA sources.

  14. Optical advantages of astigmatic aberration corrected heliostats

    NASA Astrophysics Data System (ADS)

    van Rooyen, De Wet; Schöttl, Peter; Bern, Gregor; Heimsath, Anna; Nitz, Peter

    2016-05-01

    Astigmatic aberration corrected heliostats adapt their shape in dependence of the incidence angle of the sun on the heliostat. Simulations show that this optical correction leads to a higher concentration ratio at the target and thus in a decrease in required receiver aperture in particular for smaller heliostat fields.

  15. Higher Order Aberration and Astigmatism in Children with Hyperopic Amblyopia.

    PubMed

    Choi, Seung Kwon; Chang, Ji Woong

    2016-02-01

    To investigate the changes in corneal higher-order aberration (HOA) during amblyopia treatment and the correlation between HOA and astigmatism in hyperopic amblyopia children. In this retrospective study, a total of 72 eyes from 72 patients ranging in age from 38 to 161 months were included. Patients were divided into two groups based on the degree of astigmatism. Corneal HOA was measured using a KR-1W aberrometer at the initial visit and at 3-, 6-, and 12-month follow-ups. Correlation analysis was performed to assess the association between HOA and astigmatism. A total of 72 patients were enrolled in this study, 37 of which were classified as belonging to the higher astigmatism group, while 35 were assigned to the lower astigmatism group. There was a statistically significant difference in success rate between the higher and lower astigmatism groups. In both groups, all corneal HOAs were significantly reduced during amblyopia treatment. When comparing the two groups, a significant difference in coma HOA at the 12-month follow-up was detected (p = 0.043). In the Pearson correlation test, coma HOA at the 12-month follow-up demonstrated a statistically significant correlation with astigmatism and a stronger correlation with astigmatism in the higher astigmatism group than in the lower astigmatism group (coefficient values, 0.383 and 0.284 as well as p = 0.021 and p = 0.038, respectively). HOA, particularly coma HOA, correlated with astigmatism and could exert effects in cases involving hyperopic amblyopia.

  16. Prevalence of corneal astigmatism before cataract surgery.

    PubMed

    Mohammadi, Mehran; Naderan, Mohammad; Pahlevani, Rozhin; Jahanrad, Ali

    2016-12-01

    The purpose of this study was to describe and analyze the prevalence and pattern of corneal astigmatism in cataract surgery candidates. In a prospective cross-sectional study, preoperative demographics, and keratometric and refractive values of cataract surgery candidates were collected from January 2013 to December 2014. Axial length (AL) and flat and steep keratometry measurements were optically measured by a partial coherence interferometry device (IOLMaster). This study consisted of 2156 eyes of 1317 patients with a mean age of 64.92 ± 11.48 (SD) (30-88 years). The mean of AL was 23.33 ± 1.37 mm, and the mean of corneal astigmatism was 1.12 ± 1.10 diopter (D) (range 0.0-7.00), in all patients. Furthermore, the mean of flat and steep keratometry were 43.70 ± 1.70 and 44.83 ± 1.79 D, respectively. Corneal astigmatism was 1.50 D or less in 1590 eyes (73.7 %), more than 1.50 D in 566 eyes (26.2 %), 3.00 D or more in 161 eyes (7.4 %), WTR in 796 eyes (36.9 %), ATR in 1010 eyes (46.8 %), and oblique in 350 eyes (16.2 %). ATR astigmatism axis significantly increased with the increase in age. Corneal astigmatism of most cataract surgery candidates fell between 0.50 and 1.50 D. The results of our study however is confined to our demographics might provide useful data for cataract patients, surgeons, and intraocular lens manufacturers for different purposes.

  17. [Astigmatic keratotomy with the femtosecond laser: correction of high astigmatisms after keratoplasty].

    PubMed

    Kook, D; Bühren, J; Klaproth, O K; Bauch, A S; Derhartunian, V; Kohnen, T

    2011-02-01

    The purpose of this study was to evaluate a novel technique for the correction of postoperative astigmatism after penetrating keratoplasty with the use of the femtosecond laser creating astigmatic keratotomies (femto-AK) in the scope of a retrospective case series. Clinical data of ten eyes of nine patients with high residual astigmatism after penetrating keratoplasty undergoing paired femto-AK using a 60-kHz femtosecond laser (IntraLase™, AMO) were analyzed. A new software algorithm was used to create paired arcuate cuts deep into the donor corneal button with different cut angles. Target values were refraction, uncorrected visual acuity, best corrected visual acuity, topographic data (Orbscan®, Bausch & Lomb, Rochester, NY, USA), and corneal wavefront analysis using Visual Optics Lab (VOL)-Pro 7.14 Software (Sarver and Associates). Vector analysis was performed using the Holladay, Cravy and Koch formula. Statistical analysis was performed to detect significances between visits using Student's t test. All procedures were performed without any major complications. The mean follow-up was 13 months. The mean patient age was 48.7 years. The preoperative mean uncorrected visual acuity (logMAR) was 1.27, best corrected visual acuity 0.55, mean subjective cylinder -7.4 D, and mean topometric astigmatism 9.3 D. The postoperative mean uncorrected visual acuity (logMAR) was 1.12, best corrected visual acuity 0.47, mean subjective cylinder -4.1 D, and mean topometric astigmatism 6.5 D. Differences between corneal higher order aberrations showed a high standard deviation and were therefore not statistically significant. Astigmatic keratotomy using the femtosecond laser seems to be a safe and effective tool for the correction of higher corneal astigmatisms. Due to the biomechanical properties of the cornea and missing empirical data for the novel femto-AK technology, higher numbers of patients are necessary to develop optimal treatment nomograms.

  18. Combined astigmatic keratotomy and conductive keratoplasty to correct high corneal astigmatism.

    PubMed

    Sy, Mary Ellen; Kovoor, Timmy A; Tannan, Anjali; Choi, Daniel; Deng, Sophie X; Danesh, Jennifer; Hamilton, D Rex

    2015-05-01

    To determine the safety, efficacy, and predictability of combined astigmatic keratotomy (AK) and conductive keratoplasty (CK) for treating high corneal astigmatism. University of California-Los Angeles, Los Angeles, California, USA. Retrospective case series. From January 1, 2004, to December 31, 2009, AK and CK were performed in eyes with corneal astigmatism of 5.0 diopters (D) or more after keratoplasty or trauma. The uncorrected (UDVA) and corrected (CDVA) distance visual acuities, spherical equivalent (SE), defocus equivalent, mean astigmatism, efficacy index, and complications were evaluated. In 11 eyes of 11 patients, the mean UDVA improved from 1.54 logMAR ± 0.50 (SD) preoperatively to 0.69 ± 0.62 logMAR 3 months postoperatively (P < .001) and the mean CDVA from 0.55 ± 0.62 logMAR to 0.12 ± 0.11 logMAR (P = .028). The mean SE and mean defocus equivalent decreased from -1.25 ± 5.06 D to 3.13 ± 3.06 D (P = .15) and from 7.98 ± 4.41 D to 6.97 ± 3.73 D (P = .45), respectively; these changes were not statistically significant. The mean absolute astigmatism decreased from 10.25 ± 4.71 D to 4.31 ± 2.34 D (P < .001). The mean absolute orthogonal and mean oblique astigmatism showed a statistically significant decrease. The efficacy index was 0.82. One case of wound gape after AK required suturing. No infectious keratitis, corneal perforation, or graft rejection occurred. Results indicate that combined AK and CK is safe and effective for correcting high corneal astigmatism after surgery or trauma. Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  19. Predictors of femtosecond laser intrastromal astigmatic keratotomy efficacy for astigmatism management in cataract surgery.

    PubMed

    Day, Alexander C; Stevens, Julian D

    2016-02-01

    To evaluate the factors associated with the efficacy of femtosecond laser intrastromal astigmatic keratotomy (AK). Moorfields Eye Hospital, London, United Kingdom. Prospective case series. Eyes having intrastromal AK for corneal cylinder correction were analyzed. Preoperative biometric parameters included axial length, anterior chamber depth, central corneal thickness, and Ocular Response Analyzer corneal hysteresis (CH) and corneal resistance factor (CRF). Preoperative and 1-month postoperative corneal keratometry was measured using the Topcon KR8100PA topographer-autorefractor. Astigmatic analyses were performed using the Alpins method. The study analyzed 319 eyes of 213 patients with a mean target induced astigmatism of 1.24 diopters (D) ± 0.44 (SD), mean surgically induced astigmatism (SIA) of 0.71 ± 0.43 D, and mean difference vector of 0.79 ± 0.41 D. Two multiple regression models were constructed for SIA prediction. Model 1, based on previous manual limbal relaxing incision parameters, confirmed age and astigmatism meridian (with/against the rule and oblique) to be associated with SIA in addition to AK arc length, AK start depth, and preoperative corneal cylinder magnitude. Model 2, additionally considering other parameters, found only lower CH (-0.06 DC per unit CH), a higher CRF (0.04 D per unit CRF), and the astigmatism meridian to be independent predictors of greater SIA (after adjusting for intrastromal AK arc length, start depth, and preoperative corneal cylinder). With-the-rule astigmatism was associated with a 0.13 D higher SIA than against-the-rule astigmatism, holding all other variables constant. Corneal biomechanical parameters and astigmatism meridian were independent predictors of femtosecond laser intrastromal AK efficacy even after adjusting for AK arc length, AK start depth, and preoperative corneal cylinder. Dr. Stevens is a previous consultant to Optimedica, Inc. which is now part of Abbott Medical Optics, Inc. Drs. Stevens and Day have

  20. Relationship between age, corneal astigmatism, and ocular dimensions with reference to astigmatism in eyes undergoing routine cataract surgery.

    PubMed

    Collier Wakefield, O; Annoh, R; Nanavaty, M A

    2016-04-01

    To assess the relationship between age, corneal astigmatism, and ocular dimensions with reference to astigmatism correction during cataract surgery. In this cross-sectional study of right eyes of 2247 consecutive patients attending cataract surgery preassessment, data on patient demographics, axial length (AL), anterior chamber depth (ACD), and keratometric astigmatism were collected. Astigmatism was further analyzed as against-the-rule (ATR: steepest meridian 180±30°), with-the-rule (WTR: 90±30°), and oblique (OB: 30-60°or 120-150°). Mean age, AL, and ACD were 72.28±13.84 years, 23.99±1.85 mm and 3.08 ±0.52 mm, respectively. In all, 20.4% eyes had ≤0.50 diopters (D), 55.2% had 0.51-1.50 D, 7.9% had 2.01-3.00 D, and 3.7% eyes had >3.00 D of astigmatism. Overall, 44.2% of eyes had corneal astigmatism >1.00 D. Average astigmatism in age ranges 40-49, 50-59, 60-69, 70-79, 80-89, and 90+ years were 0.82, 1.04, 1.04, 1.02, 1.15 and 2.01 D, respectively. The magnitude of preoperative astigmatism positively correlated with age (P<0.0001), with increasing and decreasing prevalence of ATR and WTR astigmatism, respectively, with advancing age. The magnitude of ATR astigmatism inversely correlates to AL (P<0.0001). ATR astigmatism is more prevalent with increasing magnitude of astigmatism (P<0.0001). A majority of patients for cataract surgery have astigmatism between 0.51 and 1.5 D. ATR astigmatism increases, whereas WTR decreases with age. ATR astigmatism inversely correlates to AL. With increasing age, the magnitude of astigmatism increases and ATR astigmatism becomes increasingly prevalent. The likelihood of a patient requiring astigmatic correction increases with age.

  1. Relationship between age, corneal astigmatism, and ocular dimensions with reference to astigmatism in eyes undergoing routine cataract surgery

    PubMed Central

    Collier Wakefield, O; Annoh, R; Nanavaty, M A

    2016-01-01

    Purpose To assess the relationship between age, corneal astigmatism, and ocular dimensions with reference to astigmatism correction during cataract surgery. Methods In this cross-sectional study of right eyes of 2247 consecutive patients attending cataract surgery preassessment, data on patient demographics, axial length (AL), anterior chamber depth (ACD), and keratometric astigmatism were collected. Astigmatism was further analyzed as against-the-rule (ATR: steepest meridian 180±30°), with-the-rule (WTR: 90±30°), and oblique (OB: 30–60°or 120–150°). Results Mean age, AL, and ACD were 72.28±13.84 years, 23.99±1.85 mm and 3.08 ±0.52 mm, respectively. In all, 20.4% eyes had ≤0.50 diopters (D), 55.2% had 0.51–1.50 D, 7.9% had 2.01–3.00 D, and 3.7% eyes had >3.00 D of astigmatism. Overall, 44.2% of eyes had corneal astigmatism >1.00 D. Average astigmatism in age ranges 40–49, 50–59, 60–69, 70–79, 80–89, and 90+ years were 0.82, 1.04, 1.04, 1.02, 1.15 and 2.01 D, respectively. The magnitude of preoperative astigmatism positively correlated with age (P<0.0001), with increasing and decreasing prevalence of ATR and WTR astigmatism, respectively, with advancing age. The magnitude of ATR astigmatism inversely correlates to AL (P<0.0001). ATR astigmatism is more prevalent with increasing magnitude of astigmatism (P<0.0001). Conclusions A majority of patients for cataract surgery have astigmatism between 0.51 and 1.5 D. ATR astigmatism increases, whereas WTR decreases with age. ATR astigmatism inversely correlates to AL. With increasing age, the magnitude of astigmatism increases and ATR astigmatism becomes increasingly prevalent. The likelihood of a patient requiring astigmatic correction increases with age. PMID:26795412

  2. Rays and fields in general astigmatic resonators

    NASA Astrophysics Data System (ADS)

    Weber, H.

    2012-05-01

    General astigmatic (GA) resonators are discussed in detail. Eigenrays, eigenmodes and eigenvalues (Gouy-factors) of this resonator are evaluated. A stability diagram for such resonators is introduced, which clearly depicts the stable and unstable regions for rays as well as for fields. Eigenrays and their stability regions are evaluated using the ABCD-law. For the beam propagation Collins' integral and the second moment method are applied. The eigenfunctions for rectangular symmetry are the generalized Hermite polynomials multiplied by the Gaussian exponential factor. It is shown that for general astigmatic resonators these polynomials are the product of normal Hermite polynomials. The generating function of the eigenfunctions depends on the special resonator. It is a useful tool for all calculations and it is determined. Furthermore it is shown that the second moment characterization of the modes is a useful and easy to handle procedure to evaluate beam width, beam divergence, radius of curvature and twist of the generalized Gauss-Hermite functions.

  3. Effects of posterior corneal astigmatism on the accuracy of AcrySof toric intraocular lens astigmatism correction

    PubMed Central

    Zhang, Bin; Ma, Jing-Xue; Liu, Dan-Yan; Guo, Cong-Rong; Du, Ying-Hua; Guo, Xiu-Jin; Cui, Yue-Xian

    2016-01-01

    AIM To evaluate the effects of posterior corneal surface measurements on the accuracy of total estimated corneal astigmatism. METHODS Fifty-seven patients with toric intraocular lens (IOL) implantation and posterior corneal astigmatism exceeding 0.5 diopter were enrolled in this retrospective study. The keratometric astigmatism (KA) and total corneal astigmatism (TA) were measured using a Pentacam rotating Scheimpflug camera to assess the outcomes of AcrySof IOL implantation. Toric IOLs were evaluated in 26 eyes using KA measurements and in 31 eyes using TA measurements. Preoperative corneal astigmatism and postoperative refractive astigmatism were recorded for statistical analysis. The cylindrical power of toric IOLs was estimated in all eyes. RESULTS In all cases, the difference of toric IOL astigmatism magnitude between KA and TA measurements for the estimation of preoperative corneal astigmatism was statistically significant. Of a total of 57 cases, the 50.88% decreased from Tn to Tn-1, and 10.53% decreased from Tn to Tn-2. In all cases, 5.26% increased from Tn to Tn+1. The mean postoperative astigmatism within the TA group was significantly lower than that in the KA group. CONCLUSION The accuracy of total corneal astigmatism calculations and the efficacy of toric IOL correction can be enhanced by measuring both the anterior and posterior corneal surfaces using a Pentacam rotating Scheimpflug camera. PMID:27672591

  4. Optimization of astigmatic particle tracking velocimeters

    NASA Astrophysics Data System (ADS)

    Rossi, Massimiliano; Kähler, Christian J.

    2014-09-01

    Astigmatic particle tracking velocimetry (APTV) has been developed in the last years to measure the three-dimensional displacement of tracer particles using a single-camera view. The measurement principle relies on an astigmatic optical system that provides aberrated particle images with a characteristic elliptical shape univocally related to the corresponding particle depth position. Because of the precision of this method, this concept is well established for measuring and controlling the distance between a CD/DVD and the reading head. The optical arrangement of an APTV system essentially consists of a primary stigmatic optics (e.g., a microscope, or a camera objective) and an astigmatic optics, typically a cylindrical lens placed in front of the camera sensor. This paper focuses on the uncertainty of APTV in the depth direction. First, an approximated analytical model is derived and experimentally validated. From the model, a set of three non-dimensional parameters that are the most significant in the optimization of the APTV performance are identified. Finally, the effect of different parameter settings and calibration approaches are studied systematically using numerical Monte Carlo simulations. The results allow for the derivation of general criteria to minimize the overall error in APTV measurements and provide the basis for reliable uncertainty estimation for a wide range of applications.

  5. Axially astigmatic surfaces: different types and their properties

    NASA Astrophysics Data System (ADS)

    Malacara-Doblado, Daniel; Malacara-Hernandez, Daniel; Garcia-Marquez, Jorge L.

    1996-12-01

    Axially astigmatic surfaces have different curvatures in orthogonal diameters. Toroidal and spherocylindrical optical surfaces are two mathematically different special cases of axially astigmatic surfaces as noted by Menchaca and Malacara (1986), but they are almost identical in the vicinity of the optical axis. The different between these two surfaces increases when the distance to the optical axis increases. We study the general properties of astigmatic surfaces and some special interesting cases.

  6. Development of a nomogram for femtosecond laser astigmatic keratotomy for astigmatism after keratoplasty.

    PubMed

    St Clair, Ryan M; Sharma, Anushree; Huang, David; Yu, Fei; Goldich, Yakov; Rootman, David; Yoo, Sonia; Cabot, Florence; Jun, Jason; Zhang, Lijun; Aldave, Anthony J

    2016-04-01

    To develop a nomogram for femtosecond laser astigmatic keratotomy (AK) to treat post-keratoplasty astigmatism. Three academic medical centers. Retrospective interventional case series. A review of post-keratoplasty femtosecond laser AK was performed. Uncorrected (UDVA) and corrected (CDVA) distance visual acuities, manifest refraction, and keratometry were recorded preoperatively and 1, 3, 6, and 12 months postoperatively. The location, length, depth, and diameter of the AK incisions were recorded, and the surgically induced astigmatic correction was related to these variables using regression analysis. One hundred forty femtosecond laser AK procedures were performed after penetrating keratoplasty (PKP) (n = 129) or deep anterior lamellar keratoplasty (DALK) (n =11), with 89 procedures (80 PKP, 9 DALK) included in the analysis. The mean CDVA improved from 20/59 (0.47 logMAR ± 0.38 [SD]) preoperatively to 20/45 (0.35 ± 0.31 logMAR) postoperatively (P = .013) (n = 46). The mean keratometric astigmatism decreased from 8.26 ± 2.90 diopters (D) preoperatively to 3.62 ± 2.59 D postoperatively (P < .0001) (n = 89). The mean refractive cylinder decreased from 6.77 ± 2.80 D preoperatively to 2.85 ± 2.57 D postoperatively (P < .0001) (n = 69). A nomogram for femtosecond laser AK to treat post-keratoplasty astigmatism was generated using regression analysis. Femtosecond laser AK significantly improved UDVA and CDVA and significantly reduced keratometric astigmatism and refractive cylinder after keratoplasty. The nomogram generated should improve the accuracy of post-keratoplasty femtosecond laser AK. None of the authors has a financial or proprietary interest in any material or method mentioned. Copyright © 2016 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  7. Astigmatic Herriott cell for optical refrigeration

    NASA Astrophysics Data System (ADS)

    Gragossian, Aram; Meng, Junwei; Ghasemkhani, Mohammadreza; Albrecht, Alexander R.; Sheik-Bahae, Mansoor

    2017-01-01

    Cooling rare-earth-doped crystals to the lowest temperature possible requires enhanced resonant absorption and high-purity crystals. Since resonant absorption decreases as the crystal is cooled, the only path forward is to increase the number of roundtrips that the laser makes inside the crystal. To achieve even lower temperatures than previously reported, we have employed an astigmatic Herriott cell to improve laser absorption at low temperatures. Preliminary results indicate improvement over previous designs. This cavity potentially enables us to use unpolarized high-power fiber lasers, and to achieve much higher cooling power for practical applications.

  8. Modes of a rotating astigmatic optical cavity

    NASA Astrophysics Data System (ADS)

    Habraken, Steven J. M.; Nienhuis, Gerard

    2008-05-01

    We generalize the concept of an optical cavity mode to the case of an astigmatic cavity that rotates about its optical axis. We show that the modes of such a cavity are both spatially and spectrally confined and use an algebraic method to study their spatial and spectral structure. Our method involves ladder operators in the spirit of the quantum-mechanical harmonic oscillator. It hinges upon their algebraic properties as well as on the group-theoretical properties of the ray (ABCD) matrix that describes the time-dependent ray dynamics of the rotating cavity.

  9. Toric intraocular lens implantation versus astigmatic keratotomy to correct astigmatism during phacoemulsification.

    PubMed

    Titiyal, Jeewan S; Khatik, Mukesh; Sharma, Namrata; Sehra, Sri Vatsa; Maharana, Parfulla K; Ghatak, Urmimala; Agarwal, Tushar; Khokhar, Sudarshan; Chawla, Bhavana

    2014-05-01

    To compare toric intraocular lens (IOL) implantation and astigmatic keratotomy (AK) in correction of astigmatism during phacoemulsification. Tertiary care hospital. Prospective randomized trial. Consecutive patients with visually significant cataract and moderate astigmatism (1.25 to 3.00 diopters [D]) were randomized into 2 groups. Temporal clear corneal 2.75 mm phacoemulsification with toric IOL implantation was performed in the toric IOL group and with 30-degree coupled AK at the 7.0 mm optic zone in the keratotomy group. The uncorrected (UDVA) and corrected (CDVA) distance visual acuities, refraction, keratometry, topography, central corneal thickness, and endothelial cell density were evaluated preoperatively and 1 day, 1 week, and 1 and 3 months postoperatively. The study enrolled 34 eyes (34 patients), 17 in each group. There was no difference in UDVA or CDVA between the 2 groups at any follow-up visit. The mean preoperative and postoperative refractive cylinder was 2.00 D ± 0.49 (SD) and 0.33 ± 0.17 D, respectively, in the toric IOL group and 1.95 ± 0.47 D and 0.57 ± 0.41 D, respectively, in the keratotomy group (P=.10). The mean residual astigmatism at 3 months was 0.44 ± 1.89 @ 160 in the toric IOL group and 0.77 ± 1.92 @ 174 in the keratotomy group (P=.61). All eyes in the toric IOL group and 14 eyes (84%) in the keratotomy group achieved a residual refractive cylinder of 1.00 D or less (P=.17). Toric IOL implantation was comparable to AK in eyes with moderate astigmatism having phacoemulsification. Copyright © 2014 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  10. Beveled Femtosecond Laser Astigmatic Keratotomy for the Treatment of High Astigmatism Post–Penetrating Keratoplasty

    PubMed Central

    Cleary, Catherine; Tang, Maolong; Ahmed, Habeeb; Fox, Martin; Huang, David

    2013-01-01

    Purpose To use beveled femtosecond laser astigmatic keratotomy (FLAK) incisions to treat high astigmatism after penetrating keratoplasty. Methods Paired FLAK incisions at a bevel angle of 135 degrees, 65% to 75% depth, and arc lengths of 60 to 90 degrees were performed using a femtosecond laser. One case of perpendicular FLAK was presented for comparison. Vector analysis was used to calculate the changes in astigmatism. Fourier domain optical coherence tomography was used to examine incision morphology. Results Wound gaping requiring suturing was observed in the case of perpendicular FLAK. Six consecutive cases of beveled FLAK were analyzed. Fourier domain optical coherence tomography showed that beveled FLAK caused a mean forward shift of Bowman layer anterior to the incisions of 126 ± 38 μm, with no wound gaping. The mean magnitude of preoperative keratometric astigmatism was 9.8 ± 2.9 diopters (D), and postoperatively it was 4.5 ± 3.2 D (P < 0.05). Uncorrected visual acuity improved from 1.24 ± 0.13 logarithm of the minimum angle of resolution preoperatively to 0.76 ± 0.38 postoperatively (P < 0.05). Best spectacle–corrected visual acuity improved from 0.43 ± 0.33 logarithm of the minimum angle of resolution preoperatively to 0.27 ± 0.24 postoperatively (P = 0.22). Visual results were reduced in 2 patients by cataract progression. Between 1 and 3 months after beveled FLAK, the keratometric cylinder was stable (<1 D change) in 5 of 6 patients, and regressed in 1 patient. No complications occurred. Conclusions Beveled FLAK incisions at varied depth are effective in the management of postkeratoplasty astigmatism. Early postoperative changes stabilized within 1 month in most patients. Further studies are needed to assess long-term outcomes. PMID:22968362

  11. [Postoperative astigmatism after penetrating corneal grafts (author's transl)].

    PubMed

    Schwöbel, M

    1975-08-04

    232 cases of penetrating grafts from 1961-1972 have been studied. 141 (60%) were evaluated for visual acuity and corneal astigmatism. Since the introduction of the running suture (1966) postoperative complications have markedly decreased, visual acuity is in the average good and even very good. Patients operated for keratokonus however show higher postoperative astigmatism than patients operatedfor other corneal diseases.

  12. Distribution of astigmatism among Sioux Indians in South Dakota.

    PubMed

    Pensyl, C D; Harrison, R A; Simpson, P; Waterbor, J W

    1997-07-01

    Previous studies have reported a greater prevalence of high astigmatism and vision disorders among Native Americans than occurs in the general U.S. population. The majority of these studies, however, have focused on Native American schoolchildren. This study assessed the distribution of astigmatism in a general clinic population at the Rosebud Indian Reservation in South Dakota. From examination of 174 patients, demographic information, visual acuities, refractive error, binocular vision status, and eye health were recorded. The data showed more high astigmatism than would be expected in a general U.S. population. Three or more diopters of astigmatism were found in 9.2% of the right eyes and 10.8% of the left eyes in the study population. High astigmatism was noted less frequently among those ages 40 years and older (3.3% right eyes, 6.3% left eyes). Most of the astigmatism was with-the-rule, but a shift toward against-the-rule and oblique astigmatism was found in older individuals. No significant gender differences were noted. The results suggest an ethnic difference in astigmatism and emphasize thee need for continued and expanded vision services for Native American populations.

  13. Refractive, anterior corneal and internal astigmatism in the pseudophakic eye.

    PubMed

    Bregnhøj, Jesper F; Mataji, Pourang; Naeser, Kristian

    2015-02-01

    To evaluate the correlation between refractive astigmatism (RA) and anterior corneal astigmatism (ACA), and determine the internal astigmatism (IA) in 184 pseudophakic eyes. The study was a prospective non-masked single-centre study. Patients were examined 8 weeks after phacoemulsification with implantation of aspheric one-piece monofocal IOLs. Examination included autokeratometry and subjective refraction. All refractive data were converted to the corneal plane. The corneal refractive index, taken to be 1.376, was used to estimate the ACA. All astigmatisms were converted to net curvital and net torsional powers with the steeper corneal plane as the reference meridian. Curvital power is the force acting along a given meridian, and torsion is the power twisting the astigmatic direction out of that plane. The internal astigmatism (IA) was calculated as the difference between RA and ACA. For curvital powers, the refractive astigmatism (KP(Φ)RA ) could be described as a function of anterior corneal astigmatic magnitude (KP(Φ)ACA ) and direction α by the multiple linear regression equation: KP(Φ)RA = -0.09 + 0.61*KP(Φ)ACA + 0.33*cos2α, (r(2) = 0.59, p < 0.0001). The average internal astigmatism amounted to 0.47 D inclined 92° relative to the steeper anterior corneal meridian. The magnitude of internal astigmatism depended on the angle α of the steeper anterior corneal meridian, averaging 0.86 D at 91° for with-the-rule, 0.37 D at 95° for oblique and 0.17 D at 97° for against-the-rule corneal astigmatisms. The internal astigmatism varies as a function of the direction of the anterior steeper corneal meridian. In patient candidates to surgical correction of astigmatism, measuring only the curvature of the anterior corneal surface and neglecting that of the posterior corneal surface can lead to inaccurate evaluation of total corneal astigmatism. © 2014 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

  14. Accommodation in Astigmatic Children During Visual Task Performance

    PubMed Central

    Harvey, Erin M.; Miller, Joseph M.; Apple, Howard P.; Parashar, Pavan; Twelker, J. Daniel; Crescioni, Mabel; Davis, Amy L.; Leonard-Green, Tina K.; Campus, Irene; Sherrill, Duane L.

    2014-01-01

    Purpose. To determine the accuracy and stability of accommodation in uncorrected children during visual task performance. Methods. Subjects were second- to seventh-grade children from a highly astigmatic population. Measurements of noncycloplegic right eye spherical equivalent (Mnc) were obtained while uncorrected subjects performed three visual tasks at near (40 cm) and distance (2 m). Tasks included reading sentences with stimulus letter size near acuity threshold and an age-appropriate letter size (high task demands) and viewing a video (low task demand). Repeated measures ANOVA assessed the influence of astigmatism, task demand, and accommodative demand on accuracy (mean Mnc) and variability (mean SD of Mnc) of accommodation. Results. For near and distance analyses, respectively, sample size was 321 and 247, mean age was 10.37 (SD 1.77) and 10.30 (SD 1.74) years, mean cycloplegic M was 0.48 (SD 1.10) and 0.79 diopters (D) (SD 1.00), and mean astigmatism was 0.99 (SD 1.15) and 0.75 D (SD 0.96). Poor accommodative accuracy was associated with high astigmatism, low task demand (video viewing), and high accommodative demand. The negative effect of accommodative demand on accuracy increased with increasing astigmatism, with the poorest accommodative accuracy observed in high astigmats (≥3.00 D) with high accommodative demand/high hyperopia (1.53 D and 2.05 D of underaccommodation for near and distant stimuli, respectively). Accommodative variability was greatest in high astigmats and was uniformly high across task condition. No/low and moderate astigmats showed higher variability for the video task than the reading tasks. Conclusions. Accuracy of accommodation is reduced in uncorrected children with high astigmatism and high accommodative demand/high hyperopia, but improves with increased visual task demand (reading). High astigmats showed the greatest variability in accommodation. PMID:25103265

  15. Pattern of astigmatism in a clinical setting in Maldives.

    PubMed

    Marasini, Sanjay

    2016-01-01

    Patterns of refractive errors have never been reported in Maldives. This study aims to dissect astigmatism and provide a general view in context of this island country. A clinic based cross sectional study was designed with 277 patients, aged ≥3.5 years and with a primary astigmatism of ≥-1.00 diopters (D). They underwent complete eye examination and a vector analysis was done. Mean age was 28.58 (SD 19.15) years. Astigmatic magnitude depended on age (p<0.05) but not on gender (p>0.05). Severity of visual impairment after refractive correction was very less, with only 2.2% having visual acuity ≤6/60. Mean spherical, spherical equivalent and astigmatic refraction were -1.35 (SD 2.94 D), -2.40 (SD 3.04) and -2.12 (SD 1.11 D), respectively. Between fellow eyes, refractive and corneal astigmatism highly correlated (0.83 and 0.73). Fifty eyes (18.1%) had an astigmatic error of ≥-3.00 D which peaked in the second and third decades of life (p<0.0001) and was corneal in origin (p<0.0001). Internal J45 and J0 tended to be more negative with increasing age, showing a trend toward against the rule astigmatism. Correlation between corneal and refractive J0 and J45 were 0.88 and 0.62 (p<0.0001). With the rule astigmatism was more common followed by against the rule and oblique. In conclusion, this study inferred that among patients with relatively higher magnitude of astigmatism attending to the clinics in Maldives, younger patients are affected more, which could possibly link to the environment, genetics and nutrition. The probable association between nutrition and astigmatism needs to be investigated to fill the gap in literature. Copyright © 2014 Spanish General Council of Optometry. Published by Elsevier Espana. All rights reserved.

  16. Lack of oblique astigmatism in the chicken eye.

    PubMed

    Maier, Felix M; Howland, Howard C; Ohlendorf, Arne; Wahl, Siegfried; Schaeffel, Frank

    2015-04-01

    Primate eyes display considerable oblique off-axis astigmatism which could provide information on the sign of defocus that is needed for emmetropization. The pattern of peripheral astigmatism is not known in the chicken eye, a common model of myopia. Peripheral astigmatism was mapped out over the horizontal visual field in three chickens, 43 days old, and in three near emmetropic human subjects, average age 34.7years, using infrared photoretinoscopy. There were no differences in astigmatism between humans and chickens in the central visual field (chicks -0.35D, humans -0.65D, n.s.) but large differences in the periphery (i.e. astigmatism at 40° in the temporal visual field: humans -4.21D, chicks -0.63D, p<0.001, unpaired t-test). The lack of peripheral astigmatism in chicks was not due to differences in corneal shape. Perhaps related to their superior peripheral optics, we found that chickens had excellent visual performance also in the far periphery. Using an automated optokinetic nystagmus paradigm, no difference was observed in spatial visual performance with vision restricted to either the central 67° of the visual field or to the periphery beyond 67°. Accommodation was elicited by stimuli presented far out in the visual field. Transscleral images of single infrared LEDs showed no sign of peripheral astigmatism. The chick may be the first terrestrial vertebrate described to lack oblique astigmatism. Since corneal shape cannot account for the difference in astigmatism in humans and chicks, it must trace back to the design of the crystalline lens. The lack of peripheral astigmatism in chicks also excludes a role in emmetropization. Copyright © 2015 Elsevier Ltd. All rights reserved.

  17. Astigmatism in underserved rural areas: a population based study.

    PubMed

    Hashemi, Hassan; Nabovati, Payam; Malekifar, Azam; Yekta, Abbasali; Ostadimoghaddam, Hadi; Jafarzadehpur, Ebrahim; Khabazkhoob, Mehdi

    2016-11-01

    Studying the prevalence of astigmatism and its related factors in underprivileged rural areas in Iran. Using random cluster sampling, two rural areas in the north and southwest of Iran were randomly selected, and 3851 persons over 1 year of age were invited to the study. In addition to recording demographics, retinoscopic refraction was conducted using baseline auto-refraction results. The prevalence of astigmatism was determined based on cylinder error cut-off points of 0.50 dioptre (D), 1.00, 2.00 and 3.00 D. Multiple logistic regression was used to assess variables' relationship with astigmatism. The prevalence of astigmatism as a cylinder error greater than 0.50 D was 35.6% (95% CI: 33.7-37.6); this was 34.0% (95% CI: 31.4-36.6) in women and 36.9% (95% CI: 33.9-39.9) in men. The lowest prevalence was seen in the 6-20 year old age group (13.6%) and the highest prevalence was found in individuals older than 70 years (82.5%). In the multiple logistic regression model, age and education level were significantly related to astigmatism. The prevalence rates of with-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism were respectively 15.0%, 17.2%, and 3.5%. The prevalence of WTR astigmatism decreased with age, while the prevalence of ATR (and oblique astigmatism to a lesser extent) increased. The prevalence of astigmatism was similar to previous studies; however, there were considerable age-related changes. In particular, the prevalence of astigmatism in elderly people was substantial and of concern, particularly given that virtually none of this age group were wearing distance spectacles. © 2016 The Authors Ophthalmic & Physiological Optics © 2016 The College of Optometrists.

  18. A unified paraxial approach to astigmatic optics.

    PubMed

    Harris, W F

    1999-07-01

    In Gaussian optics properties such as dioptric power, lateral and angular magnification and thickness are simple scalar concepts. In linear optics, the optics of thick astigmatic systems, however, these concepts generalize to three-dimensional concepts in some cases (the dioptric power of thin systems, for example) and to four-dimensional concepts in general. As a result, the quantitative treatment of these properties in astigmatic systems presents challenges to the researcher in optometry, ophthalmology, and vision science. Considerable progress has been made only in the case of dioptric power. This paper presents a generalized approach to astigmatic optics which allows different physical properties to be treated in the same way: the theory is unified and, in a sense, complete. Mathematical and statistical methods developed for treating one concept become directly applicable to others. The paraxial optical properties of any optical system are completely defined by the 4 x 4 ray transfer matrix, called here the (ray) transference. The transference defines four fundamental properties of an optical system, tentatively called here positional magnification, optical thickness, divergence, and directional magnification. They are the four 2 x 2 submatrices A, B, C, and D of the transference. Each fundamental property is a modification of a familiar concept. Divergence is the negative of dioptric power expressed as the dioptric power matrix F. The four fundamental optical properties A, B, C, and D, and the derived property F, despite being different physically, all have the same underlying mathematical structure. This fact is exploited in developing a unified theory. The theory is complete in the sense that the fundamental properties fully characterize the paraxial optics of any system. The paper presents a general treatment that applies to any of the five properties. The implications are far reaching and extend beyond what can be described in the paper. Dioptric power of

  19. Simulated astigmatism impairs academic-related performance in children.

    PubMed

    Narayanasamy, Sumithira; Vincent, Stephen J; Sampson, Geoff P; Wood, Joanne M

    2015-01-01

    Astigmatism is an important refractive condition in children. However, the functional impact of uncorrected astigmatism in this population is not well established, particularly with regard to academic performance. This study investigated the impact of simulated bilateral astigmatism on academic-related tasks before and after sustained near work in children. Twenty visually normal children (mean age: 10.8 ± 0.7 years; six males and 14 females) completed a range of standardised academic-related tests with and without 1.50 D of simulated bilateral astigmatism (with both academic-related tests and the visual condition administered in a randomised order). The simulated astigmatism was induced using a positive cylindrical lens while maintaining a plano spherical equivalent. Performance was assessed before and after 20 min of sustained near work, during two separate testing sessions. Academic-related measures included a standardised reading test (the Neale Analysis of Reading Ability), visual information processing tests (Coding and Symbol Search subtests from the Wechsler Intelligence Scale for Children) and a reading-related eye movement test (the Developmental Eye Movement test). Each participant was systematically assigned either with-the-rule (WTR, axis 180°) or against-the-rule (ATR, axis 90°) simulated astigmatism to evaluate the influence of axis orientation on any decrements in performance. Reading, visual information processing and reading-related eye movement performance were all significantly impaired by both simulated bilateral astigmatism (p < 0.001) and sustained near work (p < 0.001), however, there was no significant interaction between these factors (p > 0.05). Simulated astigmatism led to a reduction of between 5% and 12% in performance across the academic-related outcome measures, but there was no significant effect of the axis (WTR or ATR) of astigmatism (p > 0.05). Simulated bilateral astigmatism impaired children's performance on a

  20. Astigmatism and early academic readiness in preschool children.

    PubMed

    Orlansky, Gale; Wilmer, Jeremy; Taub, Marc B; Rutner, Daniella; Ciner, Elise; Gryczynski, Jan

    2015-03-01

    This study investigated the relationship between uncorrected astigmatism and early academic readiness in at-risk preschool-aged children. A vision screening and academic records review were performed on 122 three- to five-year-old children enrolled in the Philadelphia Head Start program. Vision screening results were related to two measures of early academic readiness, the teacher-reported Work Sampling System (WSS) and the parent-reported Ages and Stages Questionnaire (ASQ). Both measures assess multiple developmental and skill domains thought to be related to academic readiness. Children with astigmatism (defined as >|-0.25| in either eye) were compared with children who had no astigmatism. Associations between astigmatism and specific subscales of the WSS and ASQ were examined using parametric and nonparametric bivariate statistics and regression analyses controlling for age and spherical refractive error. Presence of astigmatism was negatively associated with multiple domains of academic readiness. Children with astigmatism had significantly lower mean scores on Personal and Social Development, Language and Literacy, and Physical Development domains of the WSS, and on Personal/Social, Communication, and Fine Motor domains of the ASQ. These differences between children with astigmatism and children with no astigmatism persisted after statistically adjusting for age and magnitude of spherical refractive error. Nonparametric tests corroborated these findings for the Language and Literacy and Physical Health and Development domains of the WSS and the Communication domain of the ASQ. The presence of astigmatism detected in a screening setting was associated with a pattern of reduced academic readiness in multiple developmental and educational domains among at-risk preschool-aged children. This study may help to establish the role of early vision screenings, comprehensive vision examinations, and the need for refractive correction to improve academic success in

  1. Influence of different types of astigmatism on visual acuity.

    PubMed

    Remón, Laura; Monsoriu, Juan A; Furlan, Walter D

    To investigate the change in visual acuity (VA) produced by different types of astigmatism (on the basis of the refractive power and position of the principal meridians) on normal accommodating eyes. The lens induced method was employed to simulate a set of 28 astigmatic blur conditions on different healthy emmetropic eyes. Additionally, 24 values of spherical defocus were also simulated on the same eyes for comparison. VA was measured in each case and the results, expressed in logMAR units, were represented against of the modulus of the dioptric power vector (blur strength). LogMAR VA varies in a linear fashion with increasing astigmatic blur, being the slope of the line dependent on the accommodative demand in each type of astigmatism. However, in each case, we found no statistically significant differences between the three axes investigated (0°, 45°, 90°). Non-statistically significant differences were found either for the VA achieved with spherical myopic defocus (MD) and mixed astigmatism (MA). VA with simple hyperopic astigmatism (SHA) was higher than with simple myopic astigmatism (SMA), however, in this case non conclusive results were obtained in terms of statistical significance. The VA achieved with imposed compound hyperopic astigmatism (CHA) was highly influenced by the eye's accommodative response. VA is correlated with the blur strength in a different way for each type of astigmatism, depending on the accommodative demand. VA is better when one of the focal lines lie on the retina irrespective of the axis orientation; accommodation favors this situation. Copyright © 2016 Spanish General Council of Optometry. Published by Elsevier España, S.L.U. All rights reserved.

  2. Risk factors for astigmatism in the Vision in Preschoolers Study.

    PubMed

    Huang, Jiayan; Maguire, Maureen G; Ciner, Elise; Kulp, Marjean Taylor; Cyert, Lynn A; Quinn, Graham E; Orel-Bixler, Deborah; Moore, Bruce; Ying, Gui-Shuang

    2014-05-01

    To determine demographic and refractive risk factors for astigmatism in the Vision in Preschoolers Study. Three- to 5-year-old Head Start preschoolers (N = 4040) from five clinical centers underwent comprehensive eye examinations by study-certified optometrists and ophthalmologists, including monocular visual acuity testing, cover testing, and cycloplegic retinoscopy. Astigmatism was defined as the presence of greater than or equal to +1.5 diopters (D) cylinder in either eye, measured with cycloplegic refraction. The associations of risk factors with astigmatism were evaluated using the odds ratio (OR) and its 95% confidence interval (CI) from logistic regression models. Among 4040 Vision in Preschoolers Study participants overrepresenting children with vision disorders, 687 (17%) had astigmatism, and most (83.8%) had with-the-rule astigmatism. In multivariate analyses, African American (OR, 1.65; 95% CI, 1.22 to 2.24), Hispanic (OR, 2.25; 95% CI, 1.62 to 3.12), and Asian (OR, 1.76; 95% CI, 1.06 to 2.93) children were more likely to have astigmatism than non-Hispanic white children, whereas American Indian children were less likely to have astigmatism than Hispanic, African American, and Asian children (p < 0.0001). Refractive error was associated with astigmatism in a nonlinear manner, with an OR of 4.50 (95% CI, 3.00 to 6.76) for myopia (≤-1.0 D in spherical equivalent) and 1.55 (95% CI, 1.29 to 1.86) for hyperopia (≥+2.0 D) when compared with children without refractive error (>-1.0 D, <+2.0 D). There was a trend of an increasing percentage of astigmatism among older children (linear trend p = 0.06). The analysis for risk factors of with-the-rule astigmatism provided similar results. Among Head Start preschoolers, Hispanic, African American, and Asian race as well as myopic and hyperopic refractive error were associated with an increased risk of astigmatism, consistent with findings from the population-based Multi-ethnic Pediatric Eye Disease Study and the

  3. Modes of an astigmatic cavity with a lenslike medium

    SciTech Connect

    Bekshaev, A.Y.; Grimblatov, V.M.

    1988-01-01

    Arbitrary lenslike astigmatic cavities are discussed on the basis of the matrix method, which gives a simple calculation scheme for determining the radiation characteristics. New equations are derived for the matrix complex parameter of an astigmatic Gaussian beam of the fundamental mode and spectrum of natural frequencies of the cavity; the rules for finding higher modes are indicated, and the stability conditions are analyzed. The basic results are in a form analogous to known equations for cylindrical cavities, and as a result, they are easily interpreted and permit a purely formal extension of many tenets of the elementary theory of open cavities to the case of complex astigmatism.

  4. Postoperative Corneal and Surgically Induced Astigmatism following Superior Approach Manual Small Incision Cataract Surgery in Patients with Preoperative Against-the-Rule Astigmatism

    PubMed Central

    Sadik, Ahmed Abdul; Mireku, Felix Agyemang; Asiedu, Frank Yeboah; Ablordeppey, Reynolds Kwame

    2016-01-01

    The aim of the study was to report postoperative corneal and surgically induced astigmatism (SIA) in patients with preoperative against-the-rule (ATR) astigmatism who underwent superior approach manual small incision cataract surgery (MSICS). 58 eyes of 58 cataract patients with preoperative ATR astigmatism were involved in this study. All patients had operable cataracts and underwent superior approach MSICS. Keratometric (K) readings were taken prior to surgery and at 12 weeks after surgery. Centroid values of SIA, preoperative astigmatism, and postoperative astigmatism were calculated using Cartesian coordinates based analysis. Wilcoxon signed rank test was used to compute statistical significance between mean preoperative and postoperative corneal astigmatism. Cohen's d was used as effect size measure. Centroid values of 1.42 D × 179, 2.48 D × 0, and 1.07 D × 1 were recorded, respectively, for preoperative astigmatism, postoperative astigmatism, and SIA. Wilcoxon signed rank test indicated that mean ± SD postoperative corneal astigmatism (2.80 ± 1.40 D) was statistically significantly greater than preoperative corneal astigmatism (1.49 ± 1.34 D), Z = −6.263, p < 0.0001. A high Cohen's d of 1.32 was found. Our results suggest statistical and clinically significant greater postoperative corneal astigmatism than preoperative corneal astigmatism for ATR astigmatism cataract patients who underwent superior approach MSICS. PMID:28116142

  5. Optical imaging module for astigmatic detection system

    SciTech Connect

    Wang, Wei-Min; Cheng, Chung-Hsiang; Molnar, Gabor; Danzebrink, Hans-Ulrich; Hwang, Ing-Shouh; Hwu, En-Te; Huang, Kuang-Yuh

    2016-05-15

    In this paper, an optical imaging module design for an astigmatic detection system (ADS) is presented. The module is based on a commercial optical pickup unit (OPU) and it contains a coaxial illuminant for illuminating a specimen. Furthermore, the imaging module facilitates viewing the specimen and the detection laser spot of the ADS with a lateral resolution of approximately 1 μm without requiring the removal of an element of the OPU. Two polarizers and one infrared filter are used to eliminate stray laser light in the OPU and stray light produced by the illuminant. Imaging modules designed for digital versatile disks (DVDs) and Blu-ray DVDs were demonstrated. Furthermore, the module can be used for imaging a small cantilever with approximate dimensions of 2 μm (width) × 5 μm (length), and therefore, it has the potential to be used in high-speed atomic force microscopy.

  6. Influence of intraocular astigmatism on the correction of myopic astigmatism by femtosecond laser small-incision lenticule extraction.

    PubMed

    Qian, Yishan; Huang, Jia; Chu, Renyuan; Zhao, Jing; Li, Meiyan; Zhou, Xingtao; Olszewski, Emily; Wang, Yutung

    2015-05-01

    To evaluate the influence of the origin of astigmatism on the correction of myopia or myopic astigmatism by femtosecond laser small-incision lenticule extraction (SMILE). Ophthalmology Department, Eye and ENT Hospital, Shanghai, China. Prospective case series. Small-incision lenticule extraction was performed to correct myopia or myopic astigmatism. Ocular residual astigmatism (ORA) was determined by vector analysis using manifest refraction and Scheimpflug camera imaging of the anterior cornea. Patients were divided into 2 groups according to ORA (high >1.0 diopter [D]; low ≤1.0 D), and procedural efficacy was compared. Patients were examined preoperatively and 1, 3, and 6 months postoperatively. This study comprised 122 right eyes of 122 patients. No significant difference was found in the preoperative manifest astigmatism (target-induced astigmatism [TIA]) between the low ORA group (n = 67) and high ORA group (n = 55). The mean postoperative manifest astigmatism was higher in the high ORA group at all postoperative timepoints (1 month: t = 2.182, P=.031; 3 months: t = 2.30, P=.023; 6 months: t = 2.193, P=.03). The mean index of success (postoperative astigmatism/TIA) was 0.68 in the high ORA group and 0.34 in the low ORA group 1 month postoperatively (t = 2.531, P=.013); 0.73 and 0.39, respectively, at 3 months (t = 2.689, P=.008); and 0.77 and 0.46, respectively, at 6 months (t = 2.105, P=.037). Small-incision lenticule extraction was effective in correcting astigmatism but may be less effective in correcting ORA. Copyright © 2015. Published by Elsevier Inc.

  7. Nonlocal conservation laws of the constant astigmatism equation

    NASA Astrophysics Data System (ADS)

    Hlaváč, Adam; Marvan, Michal

    2017-03-01

    For the constant astigmatism equation, we construct a system of nonlocal conservation laws (an abelian covering) closed under the reciprocal transformations. The corresponding potentials are functionally independent modulo a Wronskian type relation.

  8. Development and Treatment of Astigmatism-Related Amblyopia

    PubMed Central

    Harvey, Erin M.

    2009-01-01

    Blur induced by uncorrected astigmatism during early development can result in amblyopia, as evidenced by reduced best-corrected vision relative to normal, in measures of grating acuity, vernier acuity, contrast sensitivity across a range of spatial frequencies, recognition acuity, and stereoacuity. In addition, uncorrected astigmatism during early development can result in meridional amblyopia (MA), or best-corrected visual deficits that are greater for, or are present only for, specific stimulus orientations. Astigmatism-related amblyopia can be successfully treated with optical correction in children as old as school age, but the amblyopia may not be completely eliminated with optical treatment alone, and the age at which optical treatment is most effective has yet to be determined. Future research on determining the period of susceptibility of the visual system to negative effects of uncorrected astigmatism and exploration of alternative or complimentary treatment methods, in addition to optical correction, are warranted. PMID:19430327

  9. The Changing Profile of Astigmatism in Childhood: The NICER Study.

    PubMed

    O'Donoghue, Lisa; Breslin, Karen M; Saunders, Kathryn J

    2015-05-01

    We performed a prospective study of the changing profile of astigmatism in white school children in Northern Ireland. Of the 399 6- to 7-year-old and 669 12- to 13-year-old participants in Phase 1 of the Northern Ireland Childhood Errors of Refraction (NICER) study, 302 (76%) of the younger and 436 (65%) of the older cohort were re-examined three years later (Phase 2). Stratified random cluster sampling was used. Following cycloplegia (cyclopentolate HCl 1%) refractive error was recorded by the Shin-Nippon-SRW-5000 autorefractor. Astigmatism is defined as ≥ 1.00 diopters cylinder (DC). Right eye data only are presented. The prevalence of astigmatism was unchanged in both cohorts: younger cohort 17.1% (95% confidence intervals [CIs], 13.3-21.6) were astigmatic at 9 to 10 years compared to 22.9% (95% CIs, 18.3-28.2) at 6 to 7 years; older cohort, 17.5% (95% CIs, 13.9-21.7) of participants were astigmatic at 15-16 years compared to 18.4% (95% CIs, 13.4-24.8) at age 12 to 13 years. Although prevalence remained unchanged, it was not necessarily the same children who had astigmatism at both phases. Some lost astigmatism (10.0%; CIs, 7.5-13.3 younger cohort and 17.4%; CIs, 13.5-22.2 older cohort); others became astigmatic (9.1%; CIs, 6.7-12.2 younger cohort and 11.6%; CIs, 8.4-15.8 older cohort). This study presents novel data demonstrating that the astigmatic error of white children does not remain stable throughout childhood. Although prevalence of astigmatism is unchanged between ages 6 and 7 to 15 to 16 years; during this time period individual children are developing astigmatism while other children become nonastigmatic. It is difficult to predict from their refractive data who will demonstrate these changes, highlighting the importance of all children having regular eye examinations to ensure that their visual requirements are met.

  10. Patterned corneal collagen crosslinking for astigmatism: Computational modeling study

    PubMed Central

    Seven, Ibrahim; Roy, Abhijit Sinha; Dupps, William J.

    2014-01-01

    PURPOSE To test the hypothesis that spatially selective corneal stromal stiffening can alter corneal astigmatism and assess the effects of treatment orientation, pattern, and material model complexity in computational models using patient-specific geometries. SETTING Cornea and Refractive Surgery Service, Academic Eye Institute, Cleveland, Ohio, USA. DESIGN Computational modeling study. METHODS Three-dimensional corneal geometries from 10 patients with corneal astigmatism were exported from a clinical tomography system (Pentacam). Corneoscleral finite element models of each eye were generated. Four candidate treatment patterns were simulated, and the effects of treatment orientation and magnitude of stiffening on anterior curvature and aberrations were studied. The effect of material model complexity on simulated outcomes was also assessed. RESULTS Pretreatment anterior corneal astigmatism ranged from 1.22 to 3.92 diopters (D) in a series that included regular and irregular astigmatic patterns. All simulated treatment patterns oriented on the flat axis resulted in mean reductions in corneal astigmatism and depended on the pattern geometry. The linear bow-tie pattern produced a greater mean reduction in astigmatism (1.08 D ± 0.13 [SD]; range 0.74 to 1.23 D) than other patterns tested under an assumed 2-times increase in corneal stiffness, and it had a nonlinear relationship to the degree of stiffening. The mean astigmatic effect did not change significantly with a fiber- or depth-dependent model, but it did affect the coupling ratio. CONCLUSIONS In silico simulations based on patient-specific geometries suggest that clinically significant reductions in astigmatism are possible with patterned collagen crosslinking. Effect magnitude was dependent on patient-specific geometry, effective stiffening pattern, and treatment orientation. PMID:24767795

  11. Off-axis astigmatism in the isolated chicken crystalline lens.

    PubMed

    Maier, Felix; Wahl, Siegfried; Schaeffel, Frank

    2016-12-01

    The chicken eye was previously found to have little off-axis astigmatism which is not explained by its special corneal shape but rather by the optical properties of the crystalline lens. To learn more about lens design, we studied off-axis astigmatism in the chicken lens in situ and compared it to a glass lens of similar power but with homogenous refractive index. After euthanasia, enucleated eye balls were cut in the equatorial plane right behind the scleral ossicles. The anterior segment was placed in a water-filled chamber. Several thin laser beams were projected in two perpendicular meridians through the lens under various eccentricities and the focal lengths were determined. Off-axis astigmatism across the horizontal visual field was determined as the differences in power in the two meridians. The same procedure was used for the glass lens. On-axis, the chicken crystalline lens had slightly more power in the vertical than in the horizontal meridian (-2.8±0.7D (SEM)). Astigmatism flipped sign and increased with eccentricity to reach +6.1±2.1D (SEM) at 33.5deg off-axis, as expected from off-axis astigmatism. Even though this value appears high, it was still 2.5 times lower than in the glass lens. A ZEMAX model of a lens with a homogeneous index and with surface profiles taken of the natural chicken lens revealed even higher levels of off-axis astigmatism. Obviously, the natural chicken lens displays much less off-axis astigmatism than a glass lens with similar power. Since its shape does not explain the low off-axis astigmatism, it must be due to a refined internal refractive index structure. Copyright © 2016 Elsevier Ltd. All rights reserved.

  12. Vector analysis of astigmatism before and after LASIK: a comparison of two different platforms for treatment of high astigmatism.

    PubMed

    Biscevic, Alma; Bohac, Maja; Koncarevic, Mateja; Anticic, Marija; Dekaris, Iva; Patel, Sudi

    2015-12-01

    To compare the outcomes of astigmatic laser in-situ keratomileusis (LASIK) procedures between two different platforms using J0 and J45 vector analysis. Patients were divided into four groups, depending on the type of astigmatism and laser platform on which they were treated. Astigmatism was between 2 and 7 diopters (D). One hundred and thirty-five patients with myopic astigmatism (246 eyes) and 102 patients with mixed astigmatism (172 eyes) underwent unremarkable LASIK correction on Wavelight Allegretto Eye-Q 400Hz and Schwind Amaris 750S laser platform. The preoperative and postoperative sphere, negative cylinder [C] and axis (ø) of manifest refractions were subjected to vector analysis by calculations of the standard J0 (cos [4π(ø-90)/360]xC/2) and J45 (sin[4π(ø-90)/360]xC/2). Reporting the key results, we found J0 significantly reduced after LASIK in both groups (p < 0.001) but not J45. There was no significant association between individual pairs of pre and postoperative J0 & J45 values. There was no significant difference between the outcomes of the two platforms. Wavelight Allegretto 400Hz and Schwind Amaris 750S showed excellent results for treating patients with astigmatism, regardless whether it is mixed or myopic astigmatism. The J45 did not reduce significantly possibly because of the low number of eyes with oblique astigmatism. There was no genuine difference post-operatively between groups treated on two different laser platforms according to the vector analyses.

  13. Astigmatism of the Ex Vivo Human Lens: Surface and Gradient Refractive Index Age-Dependent Contributions.

    PubMed

    Birkenfeld, Judith; de Castro, Alberto; Marcos, Susana

    2015-08-01

    We estimated the contribution of the gradient refractive index (GRIN) and lens surfaces to lens astigmatism and lens astigmatic angle as a function of age in human donor lenses. Human lenses were imaged, ex vivo, with 3D-spectral optical coherence tomography (OCT) and their back focal length was measured using laser ray tracing. The contribution of lens surfaces and GRIN to lens astigmatism were evaluated by computational ray tracing on the GRIN lens and a homogenous equivalent index lens. Astigmatism magnitude and relative astigmatic angle of and between lens surfaces, GRIN lens, and lens with homogeneous refractive index were evaluated, and all results were correlated with age. The magnitude of astigmatism in the anterior lens surface decreased with age (slope = -0.005 diopters [D]/y; r = 0.397, P = 0.018). Posterior surface astigmatism and lens astigmatism were not age-dependent. Presence of GRIN did not alter significantly the magnitude or axis of the lens astigmatism. The astigmatism of GRIN lens and lens with homogeneous refractive index correlated with anterior lens surface astigmatism (GRIN, P = 3.9E - 6, r = 0.693; equivalent refractive index lens, P = 4.1E - 4, r = 0.565). The astigmatic angle of posterior surface, GRIN lens, and homogeneous refractive index lens did not change significantly with age. The axis of lens astigmatism is close to the astigmatic axis of the anterior lens surface. Age-related changes in lens astigmatism appear to be related to changes in the anterior lens astigmatism. The influence of the GRIN on lens astigmatism and the astigmatic axis is minor.

  14. The Influence of Induced Astigmatism on the Depth of Focus.

    PubMed

    Leube, Alexander; Ohlendorf, Arne; Wahl, Siegfried

    2016-10-01

    To evaluate whether an induced astigmatism influences the subjective depth of focus. Fifty-one participants aged 18 to 35 years and with a mean spherical equivalent refractive error of -0.51 ± 2.35 DS participated in the study. The accommodation was blocked with three drops of 1% cyclopentolate. Refractive errors were corrected after subjective refraction with a 4-mm artificial pupil. To evaluate the depth of focus (DoF), defocus curves with a spherical range of ±1.5 DS were assessed. The DoF was calculated as the horizontal distance at a threshold level of +0.1 logMAR from the maximum visual acuity (VA). Defocus curves were estimated binocularly during distance (500 cm) and a near vision (40 cm) for two induced axis (ATR in 0° and WTR in 90°) and for a fixed amount of astigmatic defocus of -0.5 DC. The mean natural DoF was 0.885 ± 0.316 D for far vision and 0.940 ± 0.400 D for near vision. With induced astigmatism, the DoF for far vision was significantly increased to 1.095 ± 0.421 D (p = 0.006, ANOVA) for the WTR astigmatism but not for the ATR astigmatism (1.030 ± 0.395 D; p = 0.164, ANOVA). The induced WTR astigmatism enhanced the DoF for near vision significantly to 1.144 ± 0.338 D (p = 0.04, ANOVA), and DoF with induced ATR astigmatism (0.953 ± 0.318 D) was not significantly different (p = 1.00, ANOVA). ATR-astigmatism reduced VA by +0.08 ± 0.08 logMAR (p < 0.01, t-test). With an induced WTR astigmatism of -0.5 DC, the DoF can be enhanced in the near viewing distance with a marginal loss in binocular VA. The approach of using induced WTR astigmatism can lead to novel optical treatments for presbyopia.

  15. Pattern of astigmatism in a clinical setting in Maldives☆

    PubMed Central

    Marasini, Sanjay

    2015-01-01

    Background Patterns of refractive errors have never been reported in Maldives. This study aims to dissect astigmatism and provide a general view in context of this island country. Methods A clinic based cross sectional study was designed with 277 patients, aged ≥3.5 years and with a primary astigmatism of ≥−1.00 diopters (D). They underwent complete eye examination and a vector analysis was done. Results Mean age was 28.58 (SD 19.15) years. Astigmatic magnitude depended on age (p < 0.05) but not on gender (p > 0.05). Severity of visual impairment after refractive correction was very less, with only 2.2% having visual acuity ≤6/60. Mean spherical, spherical equivalent and astigmatic refraction were −1.35 (SD 2.94 D), −2.40 (SD 3.04) and −2.12 (SD 1.11 D), respectively. Between fellow eyes, refractive and corneal astigmatism highly correlated (0.83 and 0.73). Fifty eyes (18.1%) had an astigmatic error of ≥−3.00 D which peaked in the second and third decades of life (p < 0.0001) and was corneal in origin (p < 0.0001). Internal J45 and J0 tended to be more negative with increasing age, showing a trend toward against the rule astigmatism. Correlation between corneal and refractive J0 and J45 were 0.88 and 0.62 (p < 0.0001). With the rule astigmatism was more common followed by against the rule and oblique. Conclusion In conclusion, this study inferred that among patients with relatively higher magnitude of astigmatism attending to the clinics in Maldives, younger patients are affected more, which could possibly link to the environment, genetics and nutrition. The probable association between nutrition and astigmatism needs to be investigated to fill the gap in literature. PMID:25800279

  16. Three Methods for Correction of Astigmatism during Phacoemulsification

    PubMed Central

    Mohammad-Rabei, Hossein; Mohammad-Rabei, Elham; Espandar, Goldis; Javadi, Mohammad Ali; Jafarinasab, Mohammad Reza; Hashemian, Seyed Javad; Feizi, Sepehr

    2016-01-01

    Purpose: To compare the safety and efficacy of three methods for correcting pre-existing astigmatism during phacoemulsification. Methods: This prospective, comparative, non-randomized study was conducted from March 2010 to January 2011, and included patients with keratometric astigmatism ≥1.25 D undergoing cataract surgery. Astigmatism was corrected using the following approaches: limbal relaxing incisions (LRI) on the steep meridian, extension and suturing of the phaco incision created at the steep meridian (extended-on-axis incision, EOAI), and toric intraocular lens (tIOL) implantation. Keratometric and refractive astigmatism were evaluated 1, 8, and 24 weeks postoperatively. Results: Eighty-three eyes of 72 patients (35 male and 37 female) with mean age of 62.4 ± 14.3 (range, 41-86) years were enrolled. The astigmatism was corrected by using the LRI, EOAI and tIOL implantation methods in 17, 33 and 33 eyes, respectively. Postoperative uncorrected distance visual acuity (UDVA) was significantly improved in all three groups. The difference in postoperative UDVA was not statistically significant among the study groups throughout follow-up except at week 24, when UCVA was significantly better in the tIOL group as compared to the EOAI group (P = 0.024). There is no statistically significant difference of correction index and index of success between three groups at week 24 (P = 0.085 and P = 0.085 respectively). Conclusion: There was no significant difference in astigmatism reduction among the three methods of astigmatism correction during phacoemulsification. Each of these methods can be used at the discretion of the surgeon. PMID:27413496

  17. Three Methods for Correction of Astigmatism during Phacoemulsification.

    PubMed

    Mohammad-Rabei, Hossein; Mohammad-Rabei, Elham; Espandar, Goldis; Javadi, Mohammad Ali; Jafarinasab, Mohammad Reza; Hashemian, Seyed Javad; Feizi, Sepehr

    2016-01-01

    To compare the safety and efficacy of three methods for correcting pre-existing astigmatism during phacoemulsification. This prospective, comparative, non-randomized study was conducted from March 2010 to January 2011, and included patients with keratometric astigmatism ≥1.25 D undergoing cataract surgery. Astigmatism was corrected using the following approaches: limbal relaxing incisions (LRI) on the steep meridian, extension and suturing of the phaco incision created at the steep meridian (extended-on-axis incision, EOAI), and toric intraocular lens (tIOL) implantation. Keratometric and refractive astigmatism were evaluated 1, 8, and 24 weeks postoperatively. Eighty-three eyes of 72 patients (35 male and 37 female) with mean age of 62.4 ± 14.3 (range, 41-86) years were enrolled. The astigmatism was corrected by using the LRI, EOAI and tIOL implantation methods in 17, 33 and 33 eyes, respectively. Postoperative uncorrected distance visual acuity (UDVA) was significantly improved in all three groups. The difference in postoperative UDVA was not statistically significant among the study groups throughout follow-up except at week 24, when UCVA was significantly better in the tIOL group as compared to the EOAI group (P = 0.024). There is no statistically significant difference of correction index and index of success between three groups at week 24 (P = 0.085 and P = 0.085 respectively). There was no significant difference in astigmatism reduction among the three methods of astigmatism correction during phacoemulsification. Each of these methods can be used at the discretion of the surgeon.

  18. Posterior corneal astigmatism in refractive lens exchange surgery.

    PubMed

    Rydström, Elin; Westin, Oscar; Koskela, Timo; Behndig, Anders

    2016-05-01

    To assess the anterior, posterior and total corneal spherical and astigmatic powers in patients undergoing refractive lens exchange (RLE) surgery. In 402 consecutive patients planned for RLE at Koskelas Eye Clinic, Luleå, Sweden, right eye data from pre- and postoperative subjective refraction, preoperative IOLMaster(®) biometry and Pentacam HR(®) measurements were collected. Postoperative Pentacam HR(®) data were collected for 54 of the patients. The spherical and astigmatic powers of the anterior and posterior corneal surfaces and for the total cornea were assessed and compared, and surgically, induced astigmatism was calculated using vector analysis. The spherical power of the anterior corneal surface was 48.18 ± 1.69D with an astigmatic power of 0.83 ± 0.54D. The corresponding values for the posterior surface were -6.05 ± 2,52D and 0.26 ± 0.15D, respectively. The total corneal spherical power calculated with ray tracing was 42.47 ± 2.89D with a 0.72 ± 0.48D astigmatic power, and the corresponding figures obtained by estimating the posterior corneal surface were 43.25 ± 1.51D (p < 0.001) with a 0.75 ± 0.49D astigmatic power (p = 0.003). In eyes with anterior astigmatism with-the-rule, the total corneal astigmatism is overestimated if the posterior corneal surface is estimated; in eyes, with against-the-rule astigmatism it is underestimated. Had the posterior corneal surface been measured in this material, 14.7% of the patients would have received a spheric instead of a toric IOL, or vice versa. Estimating the posterior corneal surface in RLE patients leads to systematic measurement errors that can be reduced by measuring the posterior surface. Such an approach can potentially increase the refractive outcome accuracy in RLE surgery. © 2016 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

  19. Successful Surgical Correction of Astigmatism using Customized Ablation Photorefractive Keratectomy

    PubMed Central

    TAHERI, Hakimeh; RAMIN, Shahrokh

    2016-01-01

    The aim of this study was to determine the change in the degree of astigmatism in patients treated with customized ablation photorefractive keratectomy (PRK). This is a cross-sectional study that involved 92 otherwise healthy subjects with regular and irregular astigmatism ≥ 1.25 D (mean age: 39.09 ± 7.72 years; range: 20–59 years). All study subjects were treated with customized ablation PRK using a Technolas 217p Excimer Laser System. Before and 6 months after the surgery, a refraction assessment was conducted for each subject, and the effectiveness of the surgery for correcting astigmatism was evaluated. There was a significant change in astigmatism based on the results of an automated refraction exam of -1.67 ± 1.03 D (P < 0.001), from -2.51 ± 1.45 D preoperatively to -0.87 ± 0.94 D postoperatively. There was also a significant change in subjective refraction of -2.00 ± 1.25 D (P < 0.001), from -2.46 ± 1.52 D preoperatively to -0.46 ± 0.97 D postoperatively. Therefore, our results show that customized ablation PRK is effective for correcting astigmatism ≥ 1.25 D (P < 0.001). PMID:28293648

  20. Total Corneal Astigmatism Measurements: Agreement Between 2 Rotating Scheimpflug Cameras.

    PubMed

    Savini, Giacomo; Næser, Kristian; Schiano-Lomoriello, Domenico; Ducoli, Pietro

    2017-04-01

    To investigate agreement between rotating Scheimpflug camera (Pentacam HR, Oculus) and rotating Scheimpflug camera combined with Placido disc corneal topography (Sirius, CSO) in measuring total corneal astigmatism (TCA). In this observational study, all patients undergoing cataract surgery with preoperative measurement of TCA by both devices and a validated corneal topographer (Keratron, Optikon 2000) were retrospectively evaluated. Astigmatism analysis was performed with and without vector analysis separately in eyes with with-the-rule, against-the-rule, and oblique astigmatism. Vector analysis was performed using the Næser polar system. In 130 eyes of 130 subjects, nonvectorial analysis revealed that the mean TCA values obtained with the Sirius were higher than the corresponding values given by the Pentacam HR in all subgroups, although the difference was statistically significant only in eyes with against-the-rule astigmatism (P = 0.0009). This finding was confirmed by vector analysis. A TCA magnitude difference greater than 0.5 diopters was observed in 20.8% of cases, and a TCA axis difference greater than 10 degrees was observed in 45.4% of cases. Axis differences dropped to 18.5% when only eyes with astigmatism >0.75 diopters were analyzed and 3 measurements were averaged. The mean difference in the meridional and torsional power of TCA was close to zero in all subgroups, but with relatively large standard deviations (approximately 0.5 D). Agreement between both devices in measuring TCA is only moderate with respect to both magnitude and axis orientation.

  1. Aperture referral in heterocentric astigmatic systems.

    PubMed

    Harris, William F

    2011-11-01

    Retinal blur patch, effective corneal patch, projective field, field of view and other concepts are usually regarded as disjoint concepts to be treated separately. However they have in common the fact that an aperture, often the pupil of the eye, has its effect at some other longitudinal position. Here the effect is termed aperture referral. To develop a complete and general theory of aperture referral under which many ostensibly-distinct aperture-dependent concepts become unified and of which these concepts become particular applications. The theory allows for apertures to be elliptical and decentred and refracting surfaces in an eye or any other optical system to be astigmatic, heterocentric and tilted. The optical model used is linear optics, a three-dimensional generalization of Gaussian optics. Positional and inclinational invariants are defined along a ray through an arbitrary optical system. A pencil of rays through a system is defined by an object or image point and an aperture defines a subset of the pencil called a restricted pencil. Invariants are derived for four cases: an object and an image point at finite and at infinite distances. Formulae are obtained for the generalized magnification and transverse translation and for the geometry and location of an aperture referred to any other transverse plane. A restricted pencil is defined by an aperture and an object or image point. The intersection of the restricted pencil with a transverse plane is the aperture referred to that transverse plane. Many concepts, including effective corneal patch, retinal blur patch, projective field and visual field, can now be treated routinely as special cases of the general theory: having identified the aperture, the referred aperture and the referring point one applies the general formulae directly. The formulae are exact in linear optics, explicit and give insight into relationships. Ophthalmic & Physiological Optics © 2011 The College of Optometrists.

  2. [The application of vector analysis for evaluation of astigmatism correction in the corneal refractive surgery].

    PubMed

    Zhang, Jiamei; Wang, Yan

    2016-01-01

    Since sixty percent of ametropes obtain astigmatism, which has influence on the visual quality, correcting the astigmatism is always the focus of concerns during visual correction procedures especially for the corneal refractive surgery. The postoperative spherical equivalent or residual cylindrical dioptors was used as quantitative index to evaluate the correction of astigmatism previously; however, such results neglect the effect of astigmatic axis shift on the treatment. Taking astigmatism as a vector parameter could describe the magnitude and direction of astigmatism accurately, thus it was increasingly applied in the evaluation of astigmatism correction. This paper reviews the present vector analysis methods, evaluation indexes and its application for the correction of astigmatism in the corneal refractive surgery.

  3. Status of astigmatism-corrected Czerny-Turner spectrometers

    NASA Astrophysics Data System (ADS)

    Li, Xinhang; Dong, Keyan; An, Yan; Wang, Zhenye

    2016-10-01

    In order to analysis and design the Czerny-Turner structure spectrometer with the high resolution and high energy reception, various astigmatism methods of the Czerny-Turner structure are reported. According to the location of plane grating, the astigmatism correction methods are divided into two categories, one is the plane grating in divergent illumination, another is the plane grating in parallel illumination. Basing on the different methods, the anastigmatic principle and methods are analyzed, the merits and demerits of the above methods are summarized and evaluated. The theoretical foundation for design of broadband eliminating astigmatism Czerny-Turner spectrometer and the reference value for the further design work are laid by the summary and analyzing in this paper.

  4. Quasi-Bessel beams from asymmetric and astigmatic illumination sources.

    PubMed

    Müller, Angelina; Wapler, Matthias C; Schwarz, Ulrich T; Reisacher, Markus; Holc, Katarzyna; Ambacher, Oliver; Wallrabe, Ulrike

    2016-07-25

    We study the spatial intensity distribution and the self-reconstruction of quasi-Bessel beams produced from refractive axicon lenses with edge emitting laser diodes as asymmetric and astigmatic illumination sources. Comparing these to a symmetric mono-mode fiber source, we find that the asymmetry results in a transition of a quasi-Bessel beam into a bow-tie shaped pattern and eventually to a line shaped profile at a larger distance along the optical axis. Furthermore, we analytically estimate and discuss the effects of astigmatism, substrate modes and non-perfect axicons. We find a good agreement between experiment, simulation and analytic considerations. Results include the derivation of a maximal axicon angle related to astigmatism of the illuminating beam, impact of laser diode beam profile imperfections like substrate modes and a longitudinal oscillation of the core intensity and radius caused by a rounded axicon tip.

  5. Goos-Hänchen and Imbert-Fedorov shifts for astigmatic Gaussian beams

    NASA Astrophysics Data System (ADS)

    Ornigotti, Marco; Aiello, Andrea

    2015-06-01

    In this work we investigate the role of the beam astigmatism in the Goos-Hänchen and Imbert-Fedorov shift. As a case study, we consider a Gaussian beam focused by an astigmatic lens and we calculate explicitly the corrections to the standard formulas for beam shifts due to the astigmatism induced by the lens. Our results show that the different focusing in the longitudinal and transverse direction introduced by an astigmatic lens may enhance the angular part of the shift.

  6. Prevalence of corneal astigmatism before cataract surgery in Indian population.

    PubMed

    Prasher, Pawan; Sandhu, Jasdeep Singh

    2017-06-01

    The purpose of the study was to assess the prevalence of corneal astigmatism before cataract surgery in Indian population. The setting of this study was at the Sant Sarwan Dass Charitable Eye Hospital, Jalandhar, India. This is a clinic-based retrospective study. Charts of patients who underwent cataract surgery over a two-year period were retrospectively reviewed, and preoperative keratometric measurements were collected and analyzed. The mean age of 2316 patients (2502 eyes) was 59.54 ± 10.96 years. The corneal astigmatism was less than 1.0 Dioptre (D) in 796 eyes (59.37 %), 1.0-1.99 D in 716 eyes (28.62 %), 2.0-2.99 D in 187 eyes (7.47 %) and more than 3.0 D in 114 eyes (4.56 %). The mean corneal astigmatism was 1.04 ± 1.04 D and showed a gradual increase with age after the fourth decade. The astigmatism was with-the-rule in 709 (28.34 %), against-the-rule in 1298 (51.88 %), and oblique in 598 (23.9 %) eyes. There was a shift in astigmatism from with-the-rule to against-the-rule with increase in age. Over 40 % of the Indian patients undergoing cataract surgery have more than 1.0 D of corneal astigmatism and may benefit from the use of toric intraocular lenses. These data can be useful in planning to make this technology available for the patients.

  7. The effect of astigmatism axis on visual acuity.

    PubMed

    Mimouni, Michael; Nemet, Achia; Pokroy, Russell; Sela, Tzahi; Munzer, Gur; Kaiserman, Igor

    2017-05-11

    To evaluate the effect of astigmatism axis on uncorrected distance visual acuity (UDVA) in emmetropic eyes that underwent laser refractive surgery. This retrospective study included patients who underwent laser in situ keratomileusis or photorefractive keratectomy between January 2000 and December 2015 at the Care-Vision Laser Centers, Tel Aviv, Israel. Eyes with a 3-month postoperative spherical equivalent between -0.5 D and 0.5 D were included in this study. Eyes with ocular comorbidities and planned ametropia were excluded. Study eyes were divided into 3 groups according to the steep astigmatic axis: with the rule (WTR) (60-120), oblique (31-59 or 121-149), and against the rule (ATR) (0-30 or 150-180). The UDVA of these 3 groups was compared. The oblique group was divided into oblique ATR and oblique WTR, which were compared with each other. A total of 17,416 consecutive eyes of 8,708 patients were studied. The WTR eyes (n = 10,651) had significantly better UDVA (logMAR 0.01 ± 0.08) than the oblique (n = 3,141, logMAR 0.02 ± 0.09) and ATR eyes (n = 3,624, logMAR 0.02 ± 0.10) (p<0.001). The oblique WTR group had significantly better UDVA than the oblique ATR group (p<0.001). The UDVA of the oblique and ATR groups was similar. Stepwise multiple regression analysis showed that the group accounted for 15% of the UDVA variance (p = 0.04). The astigmatic axis has a small but significant effect on UDVA in emmetropic eyes; WTR was better than oblique and ATR astigmatism. Therefore, when correcting astigmatism, it may be preferable to err towards WTR astigmatism.

  8. Impact of astigmatism and high-order aberrations on subjective best focus.

    PubMed

    Marcos, Susana; Velasco-Ocana, Miriam; Dorronsoro, Carlos; Sawides, Lucie; Hernandez, Martha; Marin, Gildas

    2015-08-01

    We studied the role of native astigmatism and ocular aberrations on best-focus setting and its shift upon induction of astigmatism in 42 subjects (emmetropes, myopes, hyperopes, with-the-rule [WTR] and against-the-rule [ATR] myopic astigmats). Stimuli were presented in a custom-developed adaptive optics simulator, allowing correction for native aberrations and astigmatism induction (+1 D; 6-mm pupil). Best-focus search consisted on randomized-step interleaved staircase method. Each subject searched best focus for four different images, and four different conditions (with/without aberration correction, with/without astigmatism induction). The presence of aberrations induced a significant shift in subjective best focus (0.4 D; p < 0.01), significantly correlated (p = 0.005) with the best-focus shift predicted from optical simulations. The induction of astigmatism produced a statistically significant shift of the best-focus setting in all groups under natural aberrations (p = 0.001), and in emmetropes and in WTR astigmats under corrected aberrations (p < 0.0001). Best-focus shift upon induced astigmatism was significantly different across groups, both for natural aberrations and AO-correction (p < 0.0001). Best focus shifted in opposite directions in WTR and ATR astigmats upon induction of astigmatism, symmetrically with respect to the best-focus shift in nonastigmatic myopes. The shifts are consistent with a bias towards vertical and horizontal retinal blur in WTR and ATR astigmats, respectively, indicating adaptation to native astigmatism.

  9. Longitudinal change and stability of refractive, keratometric, and internal astigmatism in childhood.

    PubMed

    Harvey, Erin M; Miller, Joseph M; Twelker, J Daniel; Sherrill, Duane L

    2014-12-16

    To assess longitudinal change in refractive, keratometric, and internal astigmatism in a sample of students from a population with a high prevalence of with-the-rule (WTR) astigmatism and to determine the optical origins of changes in refractive astigmatism. A retrospective analysis of longitudinal measurements of right eye refractive and keratometric astigmatism in Tohono O'odham Native American children was conducted. Changes in refractive and keratometric astigmatism per year were compared in a younger cohort (n = 1594, 3 to <11 years old) and an older cohort (n = 648, 11 to <19 years old). Data were analyzed in clinical notation (Cyl) and vector notation (J0, J45). On average, refractive astigmatism (means: 1.19 diopters [D] Cyl, +0.54 J0, +0.03 J45) resulted primarily from WTR corneal astigmatism (means: +0.85 J0, -0.02 J45) and against-the-rule (ATR) internal astigmatism (means: -0.31 J0, +0.05 J45). Mean longitudinal changes in astigmatism were statistically significant (younger cohort -0.02 D/y Cyl; older cohort +0.06 D/y Cyl). In the younger cohort, astigmatism decreased with age in low and moderate astigmats (<3.00 D) and increased with age in high astigmats (≥3.00 D). In the older cohort, astigmatism increased with age across all levels of astigmatism. Longitudinal changes in keratometric and internal astigmatism were negatively correlated in both cohorts. Cross-sectional data suggest the presence of a constant ATR contribution from internal astigmatism (0.60 D Cyl) that is close to the 0.50 D ATR constant reported by Javal and others. Highly astigmatic 3- to <11-year-old children and children older than age 11 years show a small (not clinically significant) increase in astigmatism with age. A negative correlation between changes in keratometric astigmatism and internal astigmatism suggests an active compensation that may contribute to the stability of astigmatism in Tohono O'odham children. Copyright 2015 The Association for Research in Vision and

  10. Longitudinal Change and Stability of Refractive, Keratometric, and Internal Astigmatism in Childhood

    PubMed Central

    Harvey, Erin M.; Miller, Joseph M.; Twelker, J. Daniel; Sherrill, Duane L.

    2015-01-01

    Purpose. To assess longitudinal change in refractive, keratometric, and internal astigmatism in a sample of students from a population with a high prevalence of with-the-rule (WTR) astigmatism and to determine the optical origins of changes in refractive astigmatism. Methods. A retrospective analysis of longitudinal measurements of right eye refractive and keratometric astigmatism in Tohono O'odham Native American children was conducted. Changes in refractive and keratometric astigmatism per year were compared in a younger cohort (n = 1594, 3 to <11 years old) and an older cohort (n = 648, 11 to <19 years old). Data were analyzed in clinical notation (Cyl) and vector notation (J0, J45). Results. On average, refractive astigmatism (means: 1.19 diopters [D] Cyl, +0.54 J0, +0.03 J45) resulted primarily from WTR corneal astigmatism (means: +0.85 J0, −0.02 J45) and against-the-rule (ATR) internal astigmatism (means: −0.31 J0, +0.05 J45). Mean longitudinal changes in astigmatism were statistically significant (younger cohort −0.02 D/y Cyl; older cohort +0.06 D/y Cyl). In the younger cohort, astigmatism decreased with age in low and moderate astigmats (<3.00 D) and increased with age in high astigmats (≥3.00 D). In the older cohort, astigmatism increased with age across all levels of astigmatism. Longitudinal changes in keratometric and internal astigmatism were negatively correlated in both cohorts. Conclusions. Cross-sectional data suggest the presence of a constant ATR contribution from internal astigmatism (0.60 D Cyl) that is close to the 0.50 D ATR constant reported by Javal and others. Highly astigmatic 3- to <11-year-old children and children older than age 11 years show a small (not clinically significant) increase in astigmatism with age. A negative correlation between changes in keratometric astigmatism and internal astigmatism suggests an active compensation that may contribute to the stability of astigmatism in Tohono O'odham children. PMID:25515577

  11. Myopic astigmatism a substitute for accommodation in pseudophakia.

    PubMed

    Huber, C

    1981-12-16

    The power of an intraocular lens can be calculated before surgery to make the eye emmetropic or ametropic. The physiological mechanism of accommodation however, cannot be restored with an inelastic lens. An increased depth of focus in the implanted eye can be predicted through optical principles alone, if the postoperative ametropia of the implanted eye is a simple myopic astigmatism. This increased depth of focus without accommodation was tested in artificial ametropia and found to be used in nature by the seal. To increase the precision of intraocular lens calculation the average change in corneal power induced at surgery is used to predict the postoperative corneal power. By controlled suture release in the postoperative phase, the amount of induced corneal astigmatism is adjusted to obtain a simple myopic astigmatism. Patients with an intraocular lens and a simple myopic astigmatism as a residual ametropia, are spectacle independent most of the time. They need their glasses only for driving or prolonged reading. The methods used to calculate the postoperative cornea, the postoperative anterior chamber depth and the intraocular lens are described with the corresponding calculator programs for the HP 41C calculator. Clinical results and measurements of the depth of focus are shown in a series of 50 successive implant cases.

  12. LASER BEAMS: Tunable astigmatic π/2 mode converter

    NASA Astrophysics Data System (ADS)

    Malyutin, A. A.

    2004-02-01

    The scheme of a tunable astigmatic π/2 mode converter is described. The converter provides the use of input beams with the twofold variable Rayleigh length, while variations in the optical length of the converter itself do not exceed 1/6.

  13. Corneal astigmatism analysis for toric intraocular lens implantation: precise measurements for perfect correction.

    PubMed

    Lee, Hun; Kim, Tae-Im; Kim, Eung Kweon

    2015-01-01

    Corneal astigmatism is a common refractive error observed in a significant percentage of cataract patients. Accurate measurements of the preexisting corneal astigmatism are essential in order to achieve the desired refractive outcome after toric intraocular lens (IOL) implantation. This article presents a comprehensive review of recent published literatures on methods for measuring preoperative corneal astigmatism for toric IOL implantation. A variety of instruments has been introduced and used to measure the magnitude and meridian of corneal astigmatism during preoperative assessments of cataract patients. Instruments that consider both the anterior and posterior corneal surfaces as critical factors for measuring total corneal astigmatism are expected to provide better accuracy. Although these instruments facilitate improved evaluations of corneal astigmatism and have helped minimize postoperative residual astigmatism, a perfect method to analyze preoperative corneal astigmatism has not yet been established. Perfect correction of astigmatism after toric IOL implantation by using accurate corneal astigmatism values is the goal of this surgical procedure. To achieve this, correct and precise measurements of corneal astigmatism to determine the magnitude and meridian should be obtained.

  14. Characteristics of Astigmatism in a Population of Tunisian School-Children.

    PubMed

    Chebil, Ahmed; Jedidi, Lina; Chaker, Nibrass; Kort, Fedra; Limaiem, Rym; Mghaieth, Fatma; El Matri, Leila

    2015-01-01

    To evaluate the characteristics of astigmatism in a cross-sectional study of schoolchildren in Tunisia. A random cluster design was used to recruit children from primary schools across urban and rural settings in Tunisia, from 2008 to 2010. A total of 6192 students aged 6-14-years old were enrolled. All students whose uncorrected visual acuity was worse than 20/20 underwent a complete ophthalmic examination. Astigmatism was defined as the cylinder power of 0.75 diopter (D) or greater. The prevalence of astigmatism was 6.67%. Mean cylinder power was - 1.89 ± 0.79D. The prevalence of astigmatism increased statistically significantly with age (P = 0.032). The prevalence of astigmatism was not significantly related to gender (P = 0.051). Of those with cylinder, 63.6%, 17.8%, and 18.6% schoolchildren had with with-the-rule, against-the-rule, and oblique astigmatism, respectively. ATR astigmatism was significantly higher in males (P = 0.033). There was no significant association between the student's area of residence and astigmatism (P = 0.059). Comparisons with other studies show that the prevalence of astigmatism in Tunisia is higher than in some countries. The prevalence of astigmatism increased with age but not gender. The majority of schoolchildren had with-the-rule astigmatism.

  15. The location of incision in cataract surgery and its impact on induced astigmatism.

    PubMed

    Hashemi, Hassan; Khabazkhoob, Mehdi; Soroush, Sara; Shariati, Reyhane; Miraftab, Mohammad; Yekta, Abbasali

    2016-01-01

    The purpose of the present study is a systematic review of previous studies on choosing the best incision site for the correction of astigmatism in cataract surgery and assessing the amount of surgically induced astigmatism (SIA) with each approach. Regardless of astigmatism axis, studies show that using an on-axis incision is associated with favorable results for 0.5-1.0 diopter (D) of astigmatism. In cases with more than 1.0 D astigmatism, paired on-axis incisions can be appreciably efficient in astigmatism correction and cause at least 1.5 D SIA. Considering the amount of SIA, a temporal incision is the best approach when the patient has minimal amounts of corneal astigmatism preoperatively. At higher levels of astigmatism, if no other astigmatism correction method is used simultaneously, the temporal incision is used less frequently; however, since it is associated with the least SIA, it is still the choice site when another correction method is used. The temporal incisions in cataract surgery are associated with little SIA and are appropriate choices for mild preoperative astigmatism. At higher levels of preoperative astigmatism, superior incisions are associated with better results when combined methods are not applied.

  16. Characteristics of Astigmatism in a Population of Tunisian School-Children

    PubMed Central

    Chebil, Ahmed; Jedidi, Lina; Chaker, Nibrass; Kort, Fedra; Limaiem, Rym; Mghaieth, Fatma; El Matri, Leila

    2015-01-01

    Purpose: To evaluate the characteristics of astigmatism in a cross-sectional study of schoolchildren in Tunisia. Materials and Methods: A random cluster design was used to recruit children from primary schools across urban and rural settings in Tunisia, from 2008 to 2010. A total of 6192 students aged 6–14-years old were enrolled. All students whose uncorrected visual acuity was worse than 20/20 underwent a complete ophthalmic examination. Astigmatism was defined as the cylinder power of 0.75 diopter (D) or greater. Results: The prevalence of astigmatism was 6.67%. Mean cylinder power was - 1.89 ± 0.79D. The prevalence of astigmatism increased statistically significantly with age (P = 0.032). The prevalence of astigmatism was not significantly related to gender (P = 0.051). Of those with cylinder, 63.6%, 17.8%, and 18.6% schoolchildren had with with-the-rule, against-the-rule, and oblique astigmatism, respectively. ATR astigmatism was significantly higher in males (P = 0.033). There was no significant association between the student's area of residence and astigmatism (P = 0.059). Conclusion: Comparisons with other studies show that the prevalence of astigmatism in Tunisia is higher than in some countries. The prevalence of astigmatism increased with age but not gender. The majority of schoolchildren had with-the-rule astigmatism. PMID:26180472

  17. Correction of low corneal astigmatism in cataract surgery

    PubMed Central

    Leon, Pia; Pastore, Marco Rocco; Zanei, Andrea; Umari, Ingrid; Messai, Meriem; Negro, Corrado; Tognetto, Daniele

    2015-01-01

    AIM To evaluate and compare aspheric toric intraocular lens (IOL) implantation and aspheric monofocal IOL implantation with limbal relaxing incisions (LRI) to manage low corneal astigmatism (1.0-2.0 D) in cataract surgery. METHODS A prospective randomized comparative clinical study was performed. There were randomly recruited 102 eyes (102 patients) with cataracts associated with corneal astigmatism and divided into two groups. The first group received toric IOL implantation and the second one monofocal IOL implantation with peripheral corneal relaxing incisions. Outcomes considered were: visual acuity, postoperative residual astigmatism, endothelial cell count, the need for spectacles, and patient satisfaction. To determine the postoperative toric axis, all patients who underwent the toric IOL implantation were further evaluated using an OPD Scan III (Nidek Co, Japan). Follow-up lasted 6mo. RESULTS The mean uncorrected distance visual acuity (UCVA) and the best corrected visual acuity (BCVA) demonstrated statistically significant improvement after surgery in both groups. At the end of the follow-up the UCVA was statistically better in the patients with toric IOL implants compared to those patients who underwent implantation of monofocal IOL plus LRI. The mean residual refractive astigmatism was of 0.4 D for the toric IOL group and 1.1 D for the LRI group (P<0.01). No difference was observed in the postoperative endothelial cell count between the two groups. CONCLUSION The two surgical procedures demonstrated a significant decrease in refractive astigmatism. Toric IOL implantation was more effective and predictable compared to the limbal relaxing incision. PMID:26309869

  18. Changes in Astigmatism, Densitometry, and Aberrations After SMILE for Low to High Myopic Astigmatism: A 12-Month Prospective Study.

    PubMed

    Pedersen, Iben Bach; Ivarsen, Anders; Hjortdal, Jesper

    2017-01-01

    To evaluate 12-month changes in refraction, visual outcome, corneal densitometry, and postoperative aberrations after small incision lenticule extraction (SMILE) for myopic astigmatism. This 12-month prospective clinical trial comprised 101 eyes (101 patients) treated with SMILE for myopic astigmatism with cylinder of 0.75 to 4.00 diopters (D). The preoperative, 1-week, and 1-, 3-, 6-, 9-, and 12-month examinations included measurement of manifest refraction, uncorrected distance visual acuity (UDVA), and corrected (CDVA) distance visual acuity. Astigmatic error vector analysis was performed using Al-pin's method. Densitometry and aberrations were evaluated with Pentacam HR (Oculus Optikgeräte, Wetzlar, Germany). Preoperative spherical equivalent averaged -6.78 ± 1.90 D with 1.81 ± 1.00 D in cylinder correction. After 12 months, 74% and 93% of the eyes were within ±0.50 and ±1.00 D of the attempted refraction, respectively. The logMAR UDVA and CDVA averaged 0.03 ± 0.16 and -0.08 ± 0.09, respectively. Vector analysis showed a with-the-rule undercorrection at 12 months with a mean difference vector of 0.31 D @ 91°. There was a minor counterclockwise rotation of the axis, with an arithmetic angle of error of 0.34° ± 14°. An undercorrection of approximately 11% per diopter of attempted correction was seen at 12 months. Spherical aberrations, coma, and higher order aberrations remained stable during the postoperative period (P < .09). After 12 months, no increase in densitometry could be identified. Treatment of astigmatism with SMILE seems to be predictable and effective, but with an astigmatic undercorrection of approximately 11% and a small counterclockwise rotation of the axis. [J Refract Surg. 2017;33(1):11-17.]. Copyright 2017, SLACK Incorporated.

  19. Development of a program for toric intraocular lens calculation considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and effective lens position.

    PubMed

    Eom, Youngsub; Ryu, Dongok; Kim, Dae Wook; Yang, Seul Ki; Song, Jong Suk; Kim, Sug-Whan; Kim, Hyo Myung

    2016-10-01

    To evaluate the toric intraocular lens (IOL) calculation considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and effective lens position (ELP). Two thousand samples of corneal parameters with keratometric astigmatism ≥ 1.0 D were obtained using bootstrap methods. The probability distributions for incision-induced keratometric and posterior corneal astigmatisms, as well as ELP were estimated from the literature review. The predicted residual astigmatism error using method D with an IOL add power calculator (IAPC) was compared with those derived using methods A, B, and C through Monte-Carlo simulation. Method A considered the keratometric astigmatism and incision-induced keratometric astigmatism, method B considered posterior corneal astigmatism in addition to the A method, method C considered incision-induced posterior corneal astigmatism in addition to the B method, and method D considered ELP in addition to the C method. To verify the IAPC used in this study, the predicted toric IOL cylinder power and its axis using the IAPC were compared with ray-tracing simulation results. The median magnitude of the predicted residual astigmatism error using method D (0.25 diopters [D]) was smaller than that derived using methods A (0.42 D), B (0.38 D), and C (0.28 D) respectively. Linear regression analysis indicated that the predicted toric IOL cylinder power and its axis had excellent goodness-of-fit between the IAPC and ray-tracing simulation. The IAPC is a simple but accurate method for predicting the toric IOL cylinder power and its axis considering posterior corneal astigmatism, incision-induced posterior corneal astigmatism, and ELP.

  20. Comparison of Whole Eye versus First-Surface Astigmatism in Down Syndrome.

    PubMed

    Knowlton, Rachel; Marsack, Jason D; Leach, Norman E; Herring, Ralph J; Anderson, Heather A

    2015-07-01

    Subjects with Down syndrome have structural differences in the cornea and lens, as compared with the general population. This study investigates objectively measured refractive and corneal astigmatism, as well as calculated internal astigmatism in subjects with and without Down syndrome. Refractive (Grand Seiko autorefraction) and anterior corneal astigmatism (difference between steep and flat keratometry obtained with Zeiss Atlas corneal topography) were measured in 128 subjects with Down syndrome (mean [±SD] age, 24.8 [±8.7] years) and 137 control subjects without Down syndrome (mean [±SD] age, 24.9 [±9.9] years), with one eye randomly selected for analysis per subject. Refractive astigmatism and corneal astigmatism were converted to vector notation (J0, J45) to calculate internal astigmatism (Refractive - Corneal) and then converted back to minus cylinder form. Mean [±SD] refractive astigmatism was significantly greater in subjects with Down syndrome than in control subjects (-1.94 [±1.30] DC vs. -0.66 [±0.60] DC, t = -10.16, p < 0.001), as were mean corneal astigmatism (1.70 [±1.04] DC vs. 1.02 [±0.63] DC, t = 6.38, p < 0.001) and mean internal astigmatism (-1.07 [±0.68] DC vs. -0.77 [±0.41] DC, t = -4.21, p < 0.001). A positive linear correlation between corneal and refractive astigmatism was observed for both study populations for both the J0 and J45 vectors (p < 0.001 for all comparisons; R(2) range, 0.31 to 0.74). The distributions of astigmatism orientation differed significantly between the two study populations for comparisons of corneal and calculated internal astigmatism (χ(2), p < 0.007), but not refractive astigmatism (p = 0.46). This study demonstrates that corneal astigmatism is predictive of overall refractive astigmatism in subjects with Down syndrome, as it is in the general population. The greater magnitudes of astigmatism and wider variation of astigmatism orientation in subjects with Down syndrome for refractive, corneal, and

  1. The Visual Impact of Lens-Induced Astigmatism is Linked to Habitual Axis.

    PubMed

    Hughes, Amy R; Mallen, Edward A H; Elliott, David B

    2017-02-01

    Many studies have assessed the visual impact of astigmatism by inducing it using loose trial lenses at set axes. There are conflicting opinions and some confusion about the results, but the reduction in vision is typically least with lens-induced with-the-rule astigmatism. In this study, we determined whether a participant's habitual astigmatism influences the impact of lens-induced astigmatism on distance visual acuity (VA). Participants included 35 adults (age range 19-79, average 41.3 ± 15.4 years), who were either astigmats (≥0.75DC; N = 21) or non-astigmatic controls (N = 14). Distance VA was measured using an automated FrACT (Freiburg VA) system with the participant's habitual correction, and then with the addition of a +1.00DC lens at either 90 or 180 degrees (control) or at and perpendicular to the axis of habitual astigmatism (astigmats). The reduction in VA with induced astigmatism was significantly affected by whether the participant was a with-the-rule astigmat, against-the-rule astigmat, or non-astigmat (p = 0.006). Lens-induced astigmatism axis ≈ 180 (160-20°) reduced the VA less than axis ≈ 90 (70-120°) in the control group (reduction in mean VA of 0.32 SD ± 0.10 with 95% confidence intervals of [0.27,0.37] compared to 0.42 ± 0.09 [0.37,0.47] logMAR) and with-the-rule astigmats (reduction in VA of 0.31 SD ± 0.06 [0.27,0.35] compared to 0.45 SD ± 0.12 [0.38,0.52] logMAR). The against-the-rule astigmats had a very similar reduction in VA with the ≈+1.00DC axis 180 condition compared to the ≈+1.00DC axis 90 condition (reduction in VA of 0.26 SD ± 0.09 [0.21,0.31] compared to 0.25 SD ± 0.14 [0.17,0.33] logMAR). The impact of lens-induced astigmatism was dependent on the refractive status of the participants. When investigating the impact of lens-induced astigmatism, it is important to consider the participants' habitual axis of astigmatism.

  2. Correlation Between Stereoacuity and Experimentally Induced Graded Monocular and Binocular Astigmatism

    PubMed Central

    Puthran, Neelam; Gagal, Bhavna

    2016-01-01

    Introduction Stereopsis, the highest grade of binocular single vision, is affected by various factors, such as mis-alignment of visual axes, refractive errors especially anisometropia and astigmatism, both of which may result in amblyopia. There are very few studies in literature regarding the relationship between stereoacuity and refractive errors, especially astigmatism. Aim The present study was conducted to determine the correlation between stereoacuity and experimentally induced graded astigmatism in emmetropes. Materials and Methods A randomized study was conducted on 2000 individuals of either gender, between the ages of 8-35 years, at tertiary care centre attached to a medical college during the period of August 2012 to August 2014, All subjects were emmetropic with normal binocular single vision. Participants were randomly divided into four groups of 500 individuals each. Two groups were subjected to induced myopic astigmatism, either uni-ocularly or binocularly, using + 1.0 D and + 2.0 D cylinders at varying axes i.e., 450, 900 and 1800. Similarily, the remaining two groups were subjected to induced hypermetropic astigmatism, using - 1.0 D and - 2.0D cylinders at varying axes i.e. 450, 900 and 1800. Near stereoacuity was determined by the Titmus Fly Stereo Test, both before and after induction of astigmatism. Statistical analysis was done using paired t-test and ANOVA. Results The mean stereoacuity in emmetropes was 28.81±4.97 seconds of arc. There was a decrease in stereoacuity with increase in dioptric power of astigmatism (p<0.001). Oblique astigmatism reduced the stereoacuity maximally, while stereoacuity was least affected at 180o axis. Hypermetropic astigmatism caused more deterioration in stereoacuity than myopic astigmatism. A gross reduction in stereoacuity was noted in induced monocular astigmatism as against binocular astigmatism. Conclusion This study suggests that stereoacuity is significantly affected by even minor degrees of monocular or

  3. Propagation of Riemann-Silberstein vortices through an astigmatic lens.

    PubMed

    Chen, Haitao; Gao, Zenghui; Yang, Huajun; Zou, Xuefang; Wang, Fanhou

    2012-11-01

    The propagation of Riemann-Silberstein (RS) vortices for Gaussian vortex beams with topological charges m=+1 through a lens is studied. It is shown that if there is an ideal lens, a RS vortex and a circular edge dislocation appear for Gaussian on-axis vortex beams, while only RS vortices take place for Gaussian off-axis vortex beams. In the presence of an astigmatic lens, there exist RS vortices but no edge dislocations for both Gaussian on-axis and off-axis beams. By varying the astigmatic coefficient, the off-axis parameter, and the propagation distance, the motion, creation, and annihilation of vortices may take place, and in the process, the total topological charge of RS vortices remains unchanged.

  4. Comparison of Whole Eye vs. First-Surface Astigmatism in Down Syndrome

    PubMed Central

    Knowlton, Rachel; Marsack, Jason D.; Leach, Norman E.; Herring, Ralph J.; Anderson, Heather A.

    2016-01-01

    Purpose Individuals with Down syndrome (DS) have structural differences in the cornea and lens, as compared to the general population. This study investigates objectively measured refractive and corneal astigmatism, as well as calculated internal astigmatism in subjects with and without DS. Methods Refractive (Grand Seiko autorefraction) and anterior corneal astigmatism (difference between steep and flat keratometry obtained with Zeiss Atlas corneal topography) were measured in 128 subjects with DS (mean age = 24.8±8.7 yrs) and 137 controls without DS (mean age = 24.9±9.9 yrs), with 1 eye randomly selected for analysis per subject. Refractive astigmatism and corneal astigmatism were converted to vector notation (J0, J45) to calculate internal astigmatism (Refractive – Corneal) and then converted back to minus cylinder form. Results Mean refractive astigmatism was significantly greater in subjects with DS than controls (−1.94±1.30DC vs −0.66±0.60DC, t=−10.16, p<0.001), as was mean corneal astigmatism (1.70±1.04DC vs 1.02±0.63DC, t=6.38, p<0.001) and mean internal astigmatism (−1.07±0.68DC vs −0.77±0.41DC, t=−4.21, p<0.001). A positive linear correlation between corneal and refractive astigmatism was observed for both study populations for both the J0 and J45 vectors (p<0.001 for all comparisons, R2 range = 0.31 to 0.74). The distributions of astigmatism orientation differed significantly between the two study populations when compared across all three types of astigmatism (Chi-Square, p<0.001). Conclusions This study demonstrates that corneal astigmatism is predictive of overall refractive astigmatism in individuals with DS, as it is in the general population. The greater magnitudes of astigmatism and wider variation of astigmatism orientation in individuals with DS for refractive, corneal, and calculated internal astigmatism is likely attributable to previously reported differences in the structure of the cornea and internal optical components

  5. Effects of chalazia on corneal astigmatism : Large-sized chalazia in middle upper eyelids compress the cornea and induce the corneal astigmatism.

    PubMed

    Jin, Ki Won; Shin, Young Joo; Hyon, Joon Young

    2017-03-31

    A chalazion is a common eyelid disease that causes eye morbidity due to inflammation and cosmetic disfigurement. Corneal topographic changes are important factors in corneal refractive surgery, intraocular lens power calculations for cataract surgery, and visual acuity assessments. However, the effects of chalazia on corneal astigmatism have not been thoroughly investigated. The changes in corneal astigmatism according to chalazion size and location is necessary for better outcome of ocular surgery. The aim of this study is to evaluate changes in corneal astigmatism according to chalazion size and location. In this cross-sectional study, a total of 44 eyes from 33 patients were included in the chalazion group and 70 eyes from 46 patients comprised the control group. Chalazia were classified according to location and size. An autokeratorefractometer (KR8100, Topcon; Japan) and a Galilei™ dual-Scheimpflug analyzer (Ziemer Group; Port, Switzerland) were utilized to evaluate corneal changes. Oblique astigmatism was greater in the chalazion group compared with the control group (p < 0.05). Astigmatism by simulated keratometry (simK), steep K by simK, total root mean square, second order aberration, oblique astigmatism, and vertical astigmatism were significantly greater in the upper eyelid group (p < 0.05). Astigmatism by simK, second order aberration, oblique astigmatism, and vertical astigmatism were significantly greater in the large-sized chalazion group (p < 0.05). Corneal wavefront aberration was the greatest in the upper eyelid chalazion group, whole area group, and large-sized chalazion group (p < 0.05). Large-sized chalazia in the whole upper eyelid should be treated in the early phase because they induced the greatest change in corneal topography. Chalazion should be treated before corneal topography is performed preoperatively and before the diagnosis of corneal diseases.

  6. Effect of Mitomycin C on Myopic versus Astigmatic Photorefractive Keratectomy

    PubMed Central

    Fawzy, Samah M.

    2017-01-01

    Purpose. Long-term mitomycin C (MMC) effects on photorefractive keratectomy (PRK) were compared in simple myopic and astigmatic patients. Methods. In this observational cohort study, subjects were selected based on preoperative and postoperative data collected from medical records; they were divided into simple myopia with/without MMC and myopic astigmatism with/without MMC groups. Haze, uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), subjective refraction, and K-reading were evaluated at 1-, 3-, 6-, and 12-month follow-ups. Results. One hundred fifty-nine eyes of 80 subjects (34 women and 46 men; mean age, 26.81 ± 7.74 years; range, 18–53 years; spherical powers, −0.50 to −8.00 DS; and cylindrical powers, −0.25 to −5.00 DC) were enrolled. One year postoperatively, the simple myopia with/without MMC groups showed no difference in UCVA (P = 0.187), BCVA (P = 0.163), or spherical equivalent (P = 0.163) and a significant difference (P = 0.0495) in K-reading; the haze formation difference was nonsignificant (P = 0.056). Astigmatic groups with/without MMC showed a significant difference in K-reading (P < 0.0001). MMC groups had less haze formation (P < 0.0001). Conclusion. PRK with intraoperative MMC application showed excellent visual outcomes. MMC's effect on astigmatic patients was significantly better with acceptable safety and minimal side effects. PMID:28392938

  7. The Limiting Effects of Astigmatism on Visual Performance through Periscopes

    DTIC Science & Technology

    1979-10-01

    because of visual defects. Such defects have apparently been increasing appreciably during the last generation , and it is becoming more difficult to...34-- ’y-- and /*.’.’•. ’,;-,:.’,...’: A. P. Ryan ; Naval Medical Research and Development Command Research Work Unit MF58.524. 006-2195...distribution unlimited THE LIMITING EFFECTS OF ASTIGMATISM ON VISUAL PERFORMANCE THROUGH PERISCOPES by S. M. Luria, J. A. S. Kinney, C. L. Schlichting

  8. [Results of refractive surgery in hyperopic and combined astigmatism].

    PubMed

    Vlaicu, Valeria

    2013-01-01

    The refractive surgery includes a lot of procedures for changing the refraction of the eye to obtain a better visual acuity with no glasses or contact lenses. LASIK is the most commonly performed laser refractive surgery today. The goal is to present the postoperative evolution of the refraction and visual acuity after LASIK for Mixed and Hyperopic Astigmatism. The results show that LASIK is safe and predictible if we have well performed interventions and well-selected patients.

  9. Development of the fast astigmatic auto-focus microscope system

    NASA Astrophysics Data System (ADS)

    Hsu, Wei-Yao; Lee, Chien-Shing; Chen, Po-Jui; Chen, Nien-Tsu; Chen, Fong-Zhi; Yu, Zong-Ru; Kuo, Ching-Hsiang; Hwang, Chi-Hung

    2009-04-01

    In this paper, a fast auto-focus microscope system was developed based on the astigmatic method. A collimated infrared laser beam was employed in the infinite-corrected microscope optical axis by the beam splitter and reflected by the sample surface. By embedding an astigmatic lens in the system, the reflected laser beam has different focal lengths in the sagittal and tangential planes. As the microscope's relative distance varies, the reflected laser beam shape also varies and can be detected by an embedded four-quadrant photodiode, i.e., the focus error signal (FES) can be found. Then, a fast auto-focus system can be realized by converting the FES to the microscope's defocus distance. We designed an astigmatic auto-focus system for a 20× objective lens with a ±50 µm working range, and this system could also be used for 10× and 5× objectives with ±200 µm and ±800 µm working ranges, respectively.

  10. Metrology of complex astigmatic surfaces for astronomical optics

    NASA Astrophysics Data System (ADS)

    Rolt, Stephen; Kirby, Andrew K.; Robertson, David J.

    2010-07-01

    This paper will focus on the metrology of multiple complex surfaces that are to be integrated into the KBand Multi- Object Spectrograph (KMOS). KMOS is a multi-field astronomical spectrograph designed for integration with the 8.2m diameter European Southern Observatory Very Large Telescope (VLT). There are 1080 separate optical surfaces in the design, many of them complex freeform surfaces. Optical surfaces were manufactured in aluminium by precision freeform diamond machining. This flexible technique allows the fabrication of extremely complex surfaces with an accuracy of better than 15 nm RMS over a 20 mm aperture, giving the designer great freedom in generating powerful and unorthodox designs. However, the complexity of these freeform surfaces poses a challenge to their accurate characterisation. This paper will discuss in detail the metrology of a specific freeform component in the instrument. The form of these complex astigmatic surfaces was measured using spherical wavefronts by adapting a tilted Twyman-Green Interferometer arrangement. There are eight separate designs for this type of component, each with a different orientation and magnitude of astigmatism. Careful mechanical fixturing is essential to align the astigmatic axis to the test set up. The impact of mechanical tolerances on measurement uncertainty will be discussed in detail.

  11. Correction of high amounts of astigmatism through orthokeratology. A case report

    PubMed Central

    Baertschi, Michael; Wyss, Michael

    2011-01-01

    The purpose of this case report is to introduce a method for a successful treatment of high astigmatism with a new orthokeratology design, called FOKX (Falco Kontaktlinsen, Switzerland). This novel toric orthokeratology contact lens design, the fitting approach and the performance of FOKX lenses will be illustrated in the form of a case report. Correcting astigmatism with orthokeratology offers a new perspective for all patients suffering astigmatism.

  12. Investigation of a real-time location system of corneal astigmatic axis.

    PubMed

    Zhao, Jian-Guo; Pan, An-Peng; Zheng, Ke; Yu, A-Yong

    2017-01-01

    To construct a real-time computerized location system (RCLS) to analyze and display the axis of corneal astigmatism and to compare its accuracy with the Scheimpflug method. Fifty-seven eyes of 39 volunteers with corneal astigmatism more than 1.00 diopter (D) were recruited. The RCLS was composed of a circular light-emitting diode (LED) light source, surgical microscope, surgical video system, computer and self-programming image analysis software. Scheimpflug imaging measurements (Pentacam HR, Oculus, Wetzlar, Germany) were performed on all subjects to determine the axis and power of corneal astigmatism. Thereafter, the axis of corneal astigmatism was analyzed in real-time and displayed by the RCLS on supine position, and videos were recorded. The MB-Ruler 4.0 software was used to measure the astigmatic axis. The accuracy of the RCLS was compared with the Scheimpflug method. The RCLS was able to display the axis of corneal astigmatism in real-time. The axial deviation of corneal astigmatism between the two methods was 0.63 ± 3.78° when astigmatism was 1.00 to 2.00 D and decreased to 0.06 ± 1.38° when astigmatism was greater than 2.00 D. A linear correlation of astigmatic axis was noted between the two methods: AxisRCLS = 1.01 × AxisScheimpflug - 1.02 (R(2) = 0.998, P < 0.001). The Bland-Altman analysis revealed that the RCLS agreed sufficiently well with the Scheimpflug method. The RCLS can accurately analyze and display the axis for corneal astigmatism greater than 1.00 D in real-time. The RCLS simplifies marking procedures and may have potential clinical application to improve the postoperative visual outcomes in surgical correction of corneal astigmatism.

  13. Success rates in the correction of astigmatism with toric and spherical soft contact lens fittings

    PubMed Central

    Kurna, Sevda Aydin; Şengör, Tomris; Ün, Murat; Aki, Suat

    2010-01-01

    Objectives: To evaluate success rates in the correction of astigmatism with toric and spherical soft contact lens fitting. Methods: 30 patients with soft toric lenses having more than 1.25 D of corneal astigmatism (25 eyes; Group A) or having 0.75–1.25 D of corneal astigmatism (22 eyes; Group B) and 30 patients with soft spheric lenses having 0.75–1.25 D of corneal astigmatism (28 eyes; Group C) or less than 0.75 D of corneal astigmatism (23 eyes; Group D) were included in the study. Corrected and uncorrected monocular visual acuity measurement with logMAR, biomicroscopic properties, autorefractometry and corneal topography were performed for all patients immediately before and at least 20 minutes after the application of contact lenses. Success of contact lens fitting was evaluated by three parameters: astigmatic neutralization, visual success, and retinal deviation. Results: After soft toric lens application, spheric dioptres, cylindric and keratometric astigmatism, and retinal deviation decreased significantly in Groups A and B (P < 0.05). In Group C, spheric dioptres and retinal deviation decreased (P < 0.05), while cylindric and keratometric astigmatism did not change significantly (P > 0.05). In Group D, spheric dioptres, retinal deviation, and cylindric astigmatism decreased (P < 0.05). Keratometric astigmatism did not change significantly (P > 0.05) and astigmatic neutralization even increased. Conclusions: Visual acuity and residual spherical equivalent refraction remained between tolerable limits with the use of toric and spheric contact lenses. Spherical lenses failed to mask corneal toricity during topography, while toric lenses caused central neutralization and decrease in corneal cylinder in low and moderate astigmatic eyes. PMID:20856589

  14. Astigmatism-corrected Czerny-Turner imaging spectrometer for broadband spectral simultaneity

    SciTech Connect

    Xue Qingsheng

    2011-04-01

    A low-cost, broadband, astigmatism-corrected Czerny-Turner arrangement with a fixed plane grating is proposed. A wedge cylindrical lens is used to correct astigmatism over a broadband spectral range. The principle and method of astigmatism correction are described in detail. We compare the performance of this modified Czerny-Turner arrangement with that of the traditional Czerny-Turner arrangement by using a practical Czerny-Turner imaging spectrometer example.

  15. Prevalence of Preoperative Corneal Astigmatism in Patients Undergoing Cataract Surgery at Mettapracharak Hospital, Thailand.

    PubMed

    Prakairungthong, Nauljira; Charukamnoetkanok, Puwat; Isipradit, Saichin

    2015-09-01

    To describe and analyze the demography and distribution of preoperative corneal astigmatism in patients undergoing cataract surgery at Mettapracharak Hospital. The medical records of consecutive patients who had cataract surgery between October 1, 2010 and September 30, 2011 at Mettapracharak Hospital were retrospectively reviewed and analyzed. Patient demographic and keratometric data were collected and analyzed. The present study evaluated the keratometric data in 2,688 eyes of 2,671 patients who had cataract surgery with the mean age of 66.23±10.79 years. The mean corneal astigmatism was 1.09 D (range 0.00-8.50 D). Corneal astigmatism was higher than 1.00 D in 36.6%, between 0.51 D and 1.00 D in 37.9% and 0.50 D or less in 25.5% of eyes. The mean steep keratometry and flat keratometry values were 44.89±1.52 D and 43.81±1.57 D respectively. The magnitude of corneal astigmatism was positively correlated with age (p<0. 001) and there was a tendency for corneal astigmatism to increase with age above 50 years. Female had significantly steeper corneas than male. Corneal astigmatism was mainly against-the-rule (the steepest meridian at 180±30 degrees). The type of corneal astigmatism was strongly correlated with age. Against-the-rule astigmatism increased with older age. While aging decreased with-the-rule astigmatism. The present report showed the pattern of corneal astigmatism before cataract surgery in Thai governmental hospital, approximately one third of cataract patients had more than 1.00 D of astigmatism. This finding provide the important normative reference and help ophthalmologists to plan and manage the cost-effective correction of preexisting corneal astigmatism in cataract patients to achieve the best visual outcome.

  16. Analysis of components of total astigmatism in infants and young children.

    PubMed

    Sayed, Khulood Muhammad

    2017-02-01

    The aim of this study is to examine and analyze the contribution of corneal and lenticular components of total astigmatism (TA) in infants and young children and to determine whether there is any compensation for astigmatism by the lenticular component or not. The study was conducted on 614 eyes of 307 infants and young children. Cycloplegic refraction and keratometric measures using the Hand-held Autokeratometer (Nidek Co. Ltd., Hiroishi, Japan) were done for the study group under general anesthesia in Paediatric Ophthalmology Center, Sohag City, Egypt. We divided the sample into high astigmats (total cylinder ≥ 1.00 D; mean, 1.99 ± 0.89 D; n = 431 eyes; 70 %) and normal astigmats (total cylinder ≤ 0.75 D; mean, 0.55 ± 0.22 D; n = 183; 30 %). The prevalence of corneal astigmatism (CA) ≥ 1.00 D was (73 %), any degree of lenticular astigmatism (LA) was (85 %), (LA > 0.25 D = 72 %) TA was predominantly with the rule (n = 499 eyes, 81 %). Eyes with against the rule astigmatism were (n = 33 eyes, 5.3 %) and eyes with oblique astigmatism were (n = 82 eyes; 13.3 %). Gender or age differences in TA, CA, LA, or type of astigmatism were not significant. The prevalence of astigmatism found in this population of newlyborn infants and young children was relatively high, primarily corneal, and WTR astigmatism with high prevalence of oblique astigmatism. LA was much less than previous reports (mean = -0.0044 D), associated with more hyperopic eyes and eyes with high TA. The data suggest that a compensatory process exists between CA and LA to decrease the amount of TA.

  17. Plasma channels during filamentation of a femtosecond laser pulse with wavefront astigmatism in air

    SciTech Connect

    Dergachev, A A; Kandidov, V P; Shlenov, S A; Ionin, A A; Mokrousova, D V; Seleznev, L V; Sinitsyn, D V; Sunchugasheva, E S; Shustikova, A P

    2014-12-31

    We have demonstrated experimentally and numerically the possibility of controlling parameters of plasma channels formed during filamentation of a femtosecond laser pulse by introducing astigmatism in the laser beam wavefront. It is found that weak astigmatism increases the length of the plasma channel in comparison with the case of aberration-free focusing and that strong astigmatism can cause splitting of the plasma channel into two channels located one after another on the filament axis. (interaction of laser radiation with matter. laser plasma)

  18. Properties of elementary astigmatic pencils of rays in a decentered optical system

    SciTech Connect

    Grammatin, A.P.

    1995-11-01

    Properties of elementary astigmatic pencils of rays of an optical system with small decentering are formulated using the technique based on translating astigmatism from the intermediate space of the optical system to the space of images. The results obtained are not limited by the approximations based on expansions in series and are valid for decentering-caused astigmatism of an arbitrary order. The necessity of calculating at least two elementary pencils of rays when analyzing the effect of decenterings on the astigmatism is proved. 5 refs., 3 figs.

  19. Propagation of electromagnetic multi-Gaussian Schell-model beams with astigmatic aberration in turbulent ocean.

    PubMed

    Lu, Chuanyi; Zhao, Daomu

    2016-10-10

    An analytical expression for the elements of the cross-spectral density matrix of electromagnetic multi-Gaussian Schell-model beams with astigmatic aberration propagating through the turbulent ocean is derived. We investigate the statistical characteristics of the beams on propagation in great detail. It is found that, due to astigmatism, the circular symmetry of such beams suffers a certain degree of damage in the near field. In addition, astigmatism also destroys the attractive far-field flat profiles in free space. Meanwhile, we also show that astigmatism and oceanic turbulence both have certain effects on the spectral degree of polarization.

  20. Effect of astigmatism on states of polarization of aberrant stochastic electromagnetic beams in turbulent atmosphere.

    PubMed

    Li, Jia; Chen, Yanru; Zhao, Qi; Zhou, Muchun

    2009-10-01

    The effect of astigmatism on states of polarization of aberrant stochastic electromagnetic beams in turbulent atmosphere is investigated. Using the Gaussian-Schell model source with astigmatism, the analytical formula for the degree of polarization, the orientation angle, and the degree of polarization ellipse are derived. Analytical results show that different strengths of astigmatism have different effects on states of polarization on propagation. It is also shown that when the astigmatic coefficient of sources is large enough, states of polarization are hardly affected by atmospheric turbulence and the free-space diffraction phenomenon. The sufficient conditions for propagating with invariant polarization are derived and discussed.

  1. Effect of the against the rule myopic astigmatism on the near vision of the elderly.

    PubMed

    Kordić, Rajko; Kalauz, Miro; Kuzman, Tomislav; Masnec, Sanja; Skegro, Ivan; Vidović, Tomislav; Suić-Popović, Smiljka; Cerovski, Branimir; Rezaković, Saida; Kutija, Marija Barisić

    2014-12-01

    In the two groups of patients with myopic astigmatism the uncorrected near vision was tested after catatract surgery. Each group with 20 patients ages 60-80. All patients enrolled in study have uncorrected far vision 0.5 or better on Snellen tables. In the first group patients were with the rule after surgery myopic astigmatism (1-1.50 Diopter), and in the second group were patients with against the rule after surgery myopic astigmatism (1-1.50 Diopter). Patients in the second group with against the rule astigmatism achieved significantly (p<0.01) better uncorrected near vision.

  2. Compensation of corneal oblique astigmatism by internal optics: a theoretical analysis.

    PubMed

    Liu, Tao; Thibos, Larry N

    2017-05-01

    Oblique astigmatism is a prominent optical aberration of peripheral vision caused by oblique incidence of rays striking the refracting surfaces of the cornea and crystalline lens. We inquired whether oblique astigmatism from these two sources should be expected, theoretically, to have the same or opposite signs across the visual field at various states of accommodation. Oblique astigmatism was computed across the central visual field for a rotationally-symmetric schematic-eye using optical design software. Accommodative state was varied by altering the apical radius of curvature and separation of the biconvex lens's two aspheric surfaces in a manner consistent with published biometry. Oblique astigmatism was evaluated separately for the whole eye, the cornea, and the isolated lens over a wide range of surface curvatures and asphericity values associated with the accommodating lens. We also computed internal oblique astigmatism by subtracting corneal oblique astigmatism from whole-eye oblique astigmatism. A visual field map of oblique astigmatism for the cornea in the Navarro model follows the classic, textbook description of radially-oriented axes everywhere in the field. Despite large changes in surface properties during accommodation, intrinsic astigmatism of the isolated human lens for collimated light is also radially oriented and nearly independent of accommodation both in theory and in real eyes. However, the magnitude of ocular oblique astigmatism is smaller than that of the cornea alone, indicating partial compensation by the internal optics. This implies internal oblique astigmatism (which includes wavefront propagation from the posterior surface of the cornea to the anterior surface of the lens and intrinsic lens astigmatism) must have tangentially-oriented axes. This non-classical pattern of tangential axes for internal astigmatism was traced to the influence of corneal power on the angles of incidence of rays striking the internal lens. Partial

  3. Torsional and flattening effect on corneal astigmatism after cataract surgery: a retrospective analysis.

    PubMed

    Park, Yuli; Kim, Hyun Seung

    2017-02-08

    To evaluate the torsional and flattening effect of steep meridian incisions and influence of posterior corneal astigmatism (PCA) on total corneal astigmatism (TCA) after cataract surgery. One hundred thirty-two eyes underwent cataract surgery with steep meridian 2.2 mm microcoaxial and 2.85 mm conventional clear corneal incisions. Eyes were divided into with-the-rule (WTR) astigmatism and against-the-rule (ATR) astigmatism groups depending on the steeper meridian and measured with autokeratorefractor and Pentacam® before surgery, at 1 day, 1 week, 1 and 2 months postoperatively. Polar vector analysis was used to evaluate torsional effect of steep meridian incisions. A decrease in astigmatic polar value (AKP) (+0) was observed in both keratometric and total astigmatism (TA) after 1 and 2 months, although the decrease was only statistically significant in TA (p < 0.05). The AKP(+45) was more significant in the conventional group than the microcoaxial group at 2 months postoperatively (p < 0.05, respectively). There was a significant correlation between corneal thickness of the superior quadrant and PCA in the WTR group (p = 0.028). In eyes with anterior corneal astigmatism smaller than 0.55D of WTR astigmatism and PCA greater than 0.35D of WTR astigmatism showed greater shifting of steep axis and also increment of refractive cylinder powers. In eyes with superior corneal thickness greater than 714.5 μm and PCA greater than 0.35D of WTR astigmatism, steep meridian incision may cause a significant torsional effect and off-steep meridian change, contributing to an increment of postoperative residual manifest astigmatism after cataract surgery.

  4. Assessment of Anterior, Posterior, and Total Central Corneal Astigmatism in Eyes With Keratoconus.

    PubMed

    Kamiya, Kazutaka; Shimizu, Kimiya; Igarashi, Akihito; Miyake, Toshiyuki

    2015-11-01

    To investigate the magnitudes and the axis orientations of anterior, posterior, and total central corneal astigmatism in eyes with keratoconus. Retrospective case series. This study comprised 137 eyes of 137 keratoconic patients (97 men and 40 women; mean age ± standard deviation, 36.9 ± 12.2 years). The magnitude and the axis orientation of each corneal astigmatism were determined with a rotating Scheimpflug system. The mean magnitudes of anterior, posterior, and total central corneal astigmatism were 3.93 ± 2.74 diopters (D), 0.93 ± 0.64 D, and 3.90 ± 2.75 D, respectively. With-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism of the anterior corneal surface was found in 90 eyes (65.7%), 33 eyes (24.1%), and 14 eyes (10.2%), respectively, whereas the corresponding astigmatism of the posterior corneal surface was found in 14 eyes (10.2%), 15 eyes (10.9%), and 108 eyes (78.8%), respectively. We found a significant correlation between the magnitudes of anterior and posterior corneal astigmatism (Pearson correlation coefficient r = 0.769, P < .001). The mean magnitudes of anterior and posterior corneal astigmatism were approximately 4 D and 1 D, respectively, in eyes with keratoconus. Approximately 65% and 80% of eyes showed that WTR anterior astigmatism and ATR posterior astigmatism, respectively. The presence of posterior corneal astigmatism is not necessarily negligible for the accurate astigmatic correction of toric intraocular lens implantation or rigid gas-permeable contact lens wear for keratoconus. Copyright © 2015 Elsevier Inc. All rights reserved.

  5. Longitudinal Outcomes of U.S. Air Force Pilot Applicants With Waivered Astigmatism.

    PubMed

    Andrus, David E; Haynes, Jared T; Wright, Steven T

    2017-03-01

    Current U.S. Air Force medical standards allow applicants to enter pilot training with up to 1.50 D of astigmatism. However, waivers are considered for individuals with up to 3.00 D of astigmatism. Although typically a benign finding, higher levels of astigmatism may be progressive and can be associated with corneal ectasia (e.g., keratoconus or pellucid marginal degeneration) leading to reduced visual acuity with spectacles and/or soft contact lenses. The goal of this study was to evaluate the long-term outcomes of pilot applicants waivered into training with astigmatism exceeding the aeromedical standard. Subjects were identified on the basis of their enrollment in the Excessive Astigmatism Management Group maintained by the Aeromedical Consultation Service, Ophthalmology branch at Wright-Patterson Air Force Base, Ohio. Metrics evaluated included refractive status, visual acuity, aeromedical waiver status, safety data, and the development of corneal ectasia. Seventy-six subjects were tracked for up to 10 years, with an average follow-up period of 5.5 years. Mean astigmatism at initial examination was 1.91 D, although mean astigmatism on the basis of the most recent examination was 2.19 D. Subjects with excessive astigmatism who were waivered into pilot training showed an average increase in astigmatism of slightly less than 0.05 D annually, which equates to a total increase in astigmatism of approximately 0.25 D for the duration of the study. No subjects developed ectasia or were disqualified from flying for vision or refractive reasons. No mishaps were identified with vision being a causative or contributing factor. This study supports continuation of current Air Force waiver policy, although a longer follow-up period is required to consider modifying the aeromedical standard for astigmatism. Reprint & Copyright © 2017 Association of Military Surgeons of the U.S.

  6. Relaxing incision for control of postoperative astigmatism following keratoplasty.

    PubMed

    Troutman, R C; Swinger, C

    1980-02-01

    A new technique has been presented which provides a second surgical approach to correct excessive residual astigmatism following keratoplasty. The relaxing incision procedure has advantages over wedge resection in that it can be performed at the slit lamp, it gives no initial overcorrection, and it has a much shorter postoperative course while giving rapid results without suturing. Since this technique does not appear to produce significant hyperopia and may produce a tendency toward myopia, the corneal surgeon would thus have alternative techniques from which to choose, depending, in part, on the spherical component of the refraction.

  7. LASER BEAMS: Properties of an astigmatic π/2-mode converter

    NASA Astrophysics Data System (ADS)

    Malyutin, A. A.

    2003-03-01

    The properties of the astigmatic π/2 converter are analysed upon the transformation of eigen- and non-eigenmodes, and beams of arbitrary type. It is shown that the action of the converter can be reduced to even and odd numbers of Fourier transforms performed independently in two orthogonal planes containing the optical axis of the converter. The operation of two arbitrary oriented π/2 converters in tandem is described. This scheme permits obtaining at the same plane alternatively either the object image or its Fourier transform. Examples of the numerical simulation of the radiation propagation through the examined optical schemes are presented.

  8. Propagation of the Lissajous singularity dipole through an astigmatic lens

    NASA Astrophysics Data System (ADS)

    Chen, Haitao; Gao, Zenghui; Zou, Xuefang; Huang, Weigang; Wang, Fanhou

    2013-11-01

    The propagation was investigated of a pair of Lissajous singularities of opposite singularity index called the Lissajous singularity dipole (LSD) through an astigmatic lens. It is shown that after passing through the lens the positions of the singularities are inverted and more than two LSDs occur. Changes in the degree of polarization of the LSDs as well as in the shape of the Lissajous figures also occur. In addition, Lissajous singularities may take place at the focal plane, and a single Lissajous singularity may appear and vanish under certain conditions. The results are compared with those of previous work.

  9. Induced astigmatism after diamond burr superficial keratectomy for recurrent corneal erosion.

    PubMed

    Yoo, Janie H; Choi, David M

    2009-11-01

    To report a case of induced astigmatism after diamond burr superficial keratectomy (DBSK) for recurrent corneal erosion (RCE). Case report. Review of clinical findings in a 54-year-old women with ocular history of a scleral buckling procedure for a retinal detachment from blunt trauma and phacoemulsification with intraocular lens placement. The patient presented with RCE after trauma with a mascara brush to the OD and was treated with DBSK. Postoperatively, she developed significant astigmatism. In the third postoperative week after the DBSK procedure, the patient reported of worsening vision. On corneal topography, the patient was found to have 4 diopters of induced astigmatism. The astigmatic error was followed closely by serial corneal topography; a gradual decrease in the amount of astigmatism occurred over the course of 30 weeks. Forme fruste keratoconus was suspected in the patient's contralateral eye, based on corneal topographic analysis. Induced corneal astigmatism is a previously undescribed complication that can occur after DBSK. It is unclear whether the induced astigmatism in our patient was caused by the DBSK procedure alone or whether the patient had decompensated structural integrity from forme fruste keratoconus or blunt corneal trauma or both. The authors recommend that corneal topographic analysis be appropriately considered before DBSK for RCE and that corneal astigmatism be seen as a potential complication of the procedure.

  10. Postoperative Astigmatic Outcomes Based on the Haptic Axis of Intraocular Lenses Inserted in Cataract Surgery

    PubMed Central

    Kim, In-Tae; Park, Hae-Young Lopilly

    2011-01-01

    Purpose This study was conducted to compare post-operative astigmatic outcomes of two groups, with-the-rule (WTR) and against-the-rule (ATR) astigmatism patients, according to the haptic axis of intraocular lenses (IOLs) inserted in cataract surgery. Methods Seventy-two eyes with WTR astigmatism and 79 eyes with ATR astigmatism had cataract surgery through a clear corneal temporal incision. These two groups of eyes were then each divided into 2 groups based on whether the haptic axis of the inserted IOL was at 180° or 90°. For ATR patients, the outcomes were analyzed according to the three types of IOLs. Results There was no difference in corneal astigmatism, but WTR patients with a 180° haptic axis of the inserted IOL and ATR patients with a 90° hepatic axis of the inserted IOL had a significant decrease in postoperative refractive astigmatism (p < 0.05). The changes in ATR astigmatism according to the IOL type were more effective in single-piece acrylic IOLs than in the three-piece polymethylmethacrylate haptic IOL group. Conclusions Insertion of the IOL at the 180° haptic axis in WTR patients and at 90° in ATR patients during cataract surgery may have an effect in reducing pre-existing astigmatism. This observed effect was not consistent among the different types of IOLs. PMID:21350690

  11. Astigmatism Progression in the Early Treatment for Retinopathy of Prematurity Study to 6 years of age

    PubMed Central

    Davitt, Bradley V.; Quinn, Graham E.; Wallace, David K.; Dobson, Velma; Hardy, Robert J.; Tung, Betty; Lai, Dejian; Good, William V.

    2011-01-01

    Purpose To examine the prevalence of astigmatism (≥1.00 diopter (D)) and high astigmatism (≥2.00 D) from 6 months post term due date to 6 years postnatal, in preterm children with birth weight ≤ 1251g who developed high-risk prethreshold retinopathy of prematurity (ROP) and participated in the Early Treatment for ROP (ETROP) Study. Design Observational Cohort Study Participants 401 infants who developed high-risk prethreshold ROP in one or both eyes and were randomized to early treatment (ET) versus conventional management (CM). Refractive error was measured by cycloplegic retinoscopy. Eyes were excluded if they received additional retinal, glaucoma, or cataract surgery. Intervention Eyes were randomized to receive laser photocoagulation at high-risk prethreshold ROP or to receive treatment only if threshold ROP developed. Main Outcome Measures Astigmatism and high astigmatism at each study visit. Results For both ET and CM eyes, there was a consistent increase in prevalence of astigmatism over time, increasing from 42% at 4 years to 52% by 6 years for the group of ET eyes and from 47% to 54% in the CM eyes. There was no statistically significant difference between the slopes (rate of change per month) of the ET and CM eyes for both astigmatism and high astigmatism. (P=0.75) Conclusions By 6 years of age, over 50% of eyes with high-risk prethreshold ROP developed astigmatism ≥ 1.00 D, and nearly 25% of such eyes had high astigmatism (≥ 2.00 D). Presence of astigmatism was not influenced by timing of treatment, zone of acute-phase ROP, or presence of plus disease. However, there was a trend toward higher prevalence of astigmatism and high astigmatism in eyes with ROP residua. Most astigmatism was with-the-rule (75º –105º). More eyes with Type 2 than Type 1 had astigmatism by 6 years. These findings reinforce the need for follow-up eye examinations through early grade school years in infants with high risk prethreshold ROP. PMID:21872933

  12. Agreement between total corneal astigmatism calculated by vector summation and total corneal astigmatism measured by ray tracing using Galilei double Scheimpflug analyzer.

    PubMed

    Feizi, Sepehr; Delfazayebaher, Siamak; Ownagh, Vahid; Sadeghpour, Fatemeh

    2017-08-03

    To evaluate the agreement between total corneal astigmatism calculated by vector summation of anterior and posterior corneal astigmatism (TCAVec) and total corneal astigmatism measured by ray tracing (TCARay). This study enrolled a total of 204 right eyes of 204 normal subjects. The eyes were measured using a Galilei double Scheimpflug analyzer. The measured parameters included simulated keratometric astigmatism using the keratometric index, anterior corneal astigmatism using the corneal refractive index, posterior corneal astigmatism, and TCARay. TCAVec was derived by vector summation of the astigmatism on the anterior and posterior corneal surfaces. The magnitudes and axes of TCAVec and TCARay were compared. The Pearson correlation coefficient and Bland-Altman plots were used to assess the relationship and agreement between TCAVec and TCARay, respectively. The mean TCAVec and TCARay magnitudes were 0.76±0.57D and 1.00±0.78D, respectively (P<0.001). The mean axis orientations were 85.12±30.26° and 89.67±36.76°, respectively (P=0.02). Strong correlations were found between the TCAVec and TCARay magnitudes (r=0.96, P<0.001). Moderate associations were observed between the TCAVec and TCARay axes (r=0.75, P<0.001). Bland-Altman plots produced the 95% limits of agreement for the TCAVec and TCARay magnitudes from -0.33 to 0.82D. The 95% limits of agreement between the TCAVec and TCARay axes was -43.0 to 52.1°. The magnitudes and axes of astigmatisms measured by the vector summation and ray tracing methods cannot be used interchangeably. There was a systematic error between the TCAVec and TCARay magnitudes. Copyright © 2017 Spanish General Council of Optometry. Published by Elsevier España, S.L.U. All rights reserved.

  13. [Corneal astigmatism after penetrating keratoplasty with direct and indirect sutures (author's transl)].

    PubMed

    Klemen, U M

    1976-06-01

    After a full thickness optic keratoplasty the corneal astigmatism of 116 eyes was checked. 72 cases had been operated on with indirect, 44 with direct sutures. Up to the sixth month after the operation the astigmatism was found to be equally distributed between 0.75 and 12 dpt and until the end of the second year between 0.75 and 8 dpt. Neither the way of suturing nor the diameter of the graft nor the kind of corneal lesion had any influence on the postoperative astigmatism. After six months, the height and the axis of the astigmatism remained approximately constant; however, in four cases of keratokonus followed up for nineteen years the astigmatism gradually increased.

  14. Keratometric astigmatism after ECCE in eastern Nepal. Continuous versus interrupted sutures.

    PubMed

    Sood, Archana; Thakur, Sanjay Kumar D; Kumar, Sandeep; Badhu, Badri

    2003-03-01

    The study aimed to compute and compare the keratometric astigmatism induced by wound closure with continuous and interrupted sutures in conventional extracapsular cataract extraction with intraocular lens implantation at a single centre in eastern Nepal. Sixty eyes of 60 patients were included in the study. All patients received conventional extracapsular cataract extraction and single piece modified C-loop posterior chamber intraocular lens. Thirty eyes were sutured with continuous (Group 1) and 30 eyes with interrupted sutures (Group 2). The results were analysed by the unpaired student's t-test. At the end of 6 weeks, Group 1 patients had significantly higher astigmatism (3.53 +/- 2.19D) compared to Group 2 patients (1.7 +/- 1.35). A majority of patients in both groups had with-the-rule astigmatism throughout the postoperative period. Interrupted sutures cause less astigmatism than continuous suture. The factors responsible for high astigmatism in continuous sutures call for further analysis.

  15. Anterior surface-based keratometry compared with Scheimpflug tomography-based total corneal astigmatism.

    PubMed

    Tonn, Bastian; Klaproth, Oliver Klaus; Kohnen, Thomas

    2014-12-02

    Description of total corneal refractive power (TCRP) astigmatism by ray tracing using a Scheimpflug tomographer. Analysis of Scheimpflug tomography measurements to determine 3-mm-zone TCRP astigmatism (CATCRP) by ray tracing calculations, astigmatism in 15°-zone from simulated keratometry (CASim-K), anterior-surface astigmatism (CAant), and posterior-surface astigmatism (CApost). An analysis of changes with age was performed. The error produced by estimating CATCRP using CASim-K was calculated through vector analyses. The percentages of steep meridian aligned vertically, obliquely, and horizontally of CAant and CApost were calculated. A total of 3818 healthy, previously unoperated eyes were analyzed. The mean magnitude of CApost was -0.33 diopter (D). A vertically aligned steep meridian (60° to 120°) was found in 71.2% of eyes for CAant and in 88.8% for CApost. With increasing age, the occurrence of steep meridian aligned horizontally in CAant increased from 9.1% (age 20-29 years) to 31.8% (70-79 years), while vertical alignment decreased from 77.4% to 48.1%. Alignment of CApost mostly remained vertical (90.9%-80.7%). When CAant is vertical, CApost is vertical in 97% and CASim-K overestimates total corneal astigmatism (mean 0.11 ± 0.22 D). When CAant is horizontal, 18% of CApost is horizontal and CASim-K underestimates (mean 0.26 ± 0.31 D) total corneal astigmatism. The mean vector difference between CATCRP and CASim-K was 0.18 at 178° and exceeded 0.50 D in 9% of eyes. Total corneal astigmatism is overestimated by CASim-K in eyes with with-the-rule astigmatism and cannot be predicted safely in eyes that do not have with-the-rule astigmatism by anterior measurements only. Copyright 2015 The Association for Research in Vision and Ophthalmology, Inc.

  16. Topography-Guided Transepithelial Surface Ablation in the Treatment of Moderate to High Astigmatism.

    PubMed

    Chen, Xiangjun; Stojanovic, Aleksandar; Simonsen, David; Wang, Xiaorui; Liu, Yanhua; Utheim, Tor Paaske

    2016-06-01

    To analyze the outcomes of treatment of astigmatism of 2.00 diopters (D) or greater with topography-guided transepithelial surface ablation. Retrospective analysis of a series of 206 eyes divided into two groups: myopic astigmatism (153 eyes) and mixed astigmatism (53 eyes). All cases were treated with topography-guided transepithelial surface ablation. Efficacy, safety, and predictability were evaluated, and vector analysis of cylindrical correction was performed. The median preoperative spherical equivalent was -2.63 and -0.63 D for the myopic and mixed astigmatism groups, respectively, with median cylinder of -2.50 D. Postoperative uncorrected distance visual acuity was 20/20 or better in 92% and 83% of eyes in the myopic and mixed astigmatism groups, respectively; the corresponding efficacy indices were 1.00 and 0.96 and residual astigmatism of 0.50 D or less was present in 82.4% and 56.7% of eyes in the myopic and mixed astigmatism groups, respectively. The arithmetic mean magnitude of the difference vector was 0.38 (myopic) and 0.65 (mixed) D. Difference vector magnitude was positively correlated with the magnitude of target induced astigmatism in both groups. The geometric mean coefficient of adjustment index was 1.04 and 1.19, representing undercorrection of 4% and 19% in the myopic and mixed astigmatism groups, respectively. Topography-guided transepithelial ablation is a safe, effective, and predictable treatment for moderate to high astigmatism. [J Refract Surg. 2016;32(6):418-425.]. Copyright 2016, SLACK Incorporated.

  17. Quasi two-dimensional astigmatic solitons in soft chiral metastructures

    NASA Astrophysics Data System (ADS)

    Laudyn, Urszula A.; Jung, Paweł S.; Karpierz, Mirosław A.; Assanto, Gaetano

    2016-03-01

    We investigate a non-homogeneous layered structure encompassing dual spatial dispersion: continuous diffraction in one transverse dimension and discrete diffraction in the orthogonal one. Such dual diffraction can be balanced out by one and the same nonlinear response, giving rise to light self-confinement into astigmatic spatial solitons: self-focusing can compensate for the spreading of a bell-shaped beam, leading to quasi-2D solitary wavepackets which result from 1D transverse self-localization combined with a discrete soliton. We demonstrate such intensity-dependent beam trapping in chiral soft matter, exhibiting one-dimensional discrete diffraction along the helical axis and one-dimensional continuous diffraction in the orthogonal plane. In nematic liquid crystals with suitable birefringence and chiral arrangement, the reorientational nonlinearity is shown to support bell-shaped solitary waves with simple astigmatism dependent on the medium birefringence as well as on the dual diffraction of the input wavepacket. The observations are in agreement with a nonlinear nonlocal model for the all-optical response.

  18. Quasi two-dimensional astigmatic solitons in soft chiral metastructures

    PubMed Central

    Laudyn, Urszula A.; Jung, Paweł S.; Karpierz, Mirosław A.; Assanto, Gaetano

    2016-01-01

    We investigate a non-homogeneous layered structure encompassing dual spatial dispersion: continuous diffraction in one transverse dimension and discrete diffraction in the orthogonal one. Such dual diffraction can be balanced out by one and the same nonlinear response, giving rise to light self-confinement into astigmatic spatial solitons: self-focusing can compensate for the spreading of a bell-shaped beam, leading to quasi-2D solitary wavepackets which result from 1D transverse self-localization combined with a discrete soliton. We demonstrate such intensity-dependent beam trapping in chiral soft matter, exhibiting one-dimensional discrete diffraction along the helical axis and one-dimensional continuous diffraction in the orthogonal plane. In nematic liquid crystals with suitable birefringence and chiral arrangement, the reorientational nonlinearity is shown to support bell-shaped solitary waves with simple astigmatism dependent on the medium birefringence as well as on the dual diffraction of the input wavepacket. The observations are in agreement with a nonlinear nonlocal model for the all-optical response. PMID:26975651

  19. Results of radial and astigmatic keratotomy by beginning refractive surgeons.

    PubMed

    Friedberg, M L; Imperia, P S; Elander, R; Alcala, P L; Maloney, R K; Holland, G N

    1993-05-01

    There is little information available on the results of radial and astigmatic keratotomy surgery that is performed by beginning refractive surgeons. A retrospective review of all refractive keratotomies performed by Corneal Fellows in the University of California, Los Angeles, Department of Ophthalmology between October 1985 and October 1991 was performed. Data from all eyes with at least 3 months of follow-up were analyzed. Visual acuity, refractive error, and complication rates were compared with published case series. The mean preoperative spherical equivalent for the 79 eyes analyzed was -3.97 diopters (D) (range, -0.75 to -8.50 D). The mean postoperative spherical equivalent was -0.44 D (range, +1.50 to -3.88 D). The postoperative spherical equivalent was within 1.00 D of emmetropia in 85% of eyes, and uncorrected visual acuity was 20/40 or better in 94% of eyes. There were no vision-threatening complications. No patient lost more than one line of best-corrected visual acuity. Radial and astigmatic keratotomies that are performed by beginning refractive surgeons in a supervised setting can be safe and effective procedures with results comparable with those obtained by experienced refractive surgeons.

  20. Quasi two-dimensional astigmatic solitons in soft chiral metastructures.

    PubMed

    Laudyn, Urszula A; Jung, Paweł S; Karpierz, Mirosław A; Assanto, Gaetano

    2016-03-15

    We investigate a non-homogeneous layered structure encompassing dual spatial dispersion: continuous diffraction in one transverse dimension and discrete diffraction in the orthogonal one. Such dual diffraction can be balanced out by one and the same nonlinear response, giving rise to light self-confinement into astigmatic spatial solitons: self-focusing can compensate for the spreading of a bell-shaped beam, leading to quasi-2D solitary wavepackets which result from 1D transverse self-localization combined with a discrete soliton. We demonstrate such intensity-dependent beam trapping in chiral soft matter, exhibiting one-dimensional discrete diffraction along the helical axis and one-dimensional continuous diffraction in the orthogonal plane. In nematic liquid crystals with suitable birefringence and chiral arrangement, the reorientational nonlinearity is shown to support bell-shaped solitary waves with simple astigmatism dependent on the medium birefringence as well as on the dual diffraction of the input wavepacket. The observations are in agreement with a nonlinear nonlocal model for the all-optical response.

  1. Accuracy of Total Corneal Astigmatism Measurements With a Scheimpflug Imager and a Color Light-Emitting Diode Corneal Topographer.

    PubMed

    Klijn, Stijn; Reus, Nicolaas J; van der Sommen, Charlotte M; Sicam, Victor Arni D P

    2016-07-01

    To determine the accuracy of total corneal astigmatism measurements with a Scheimpflug imager and a color light-emitting diode corneal topographer, and to compare the accuracy of total corneal astigmatism measurements with the accuracy of measurements that are based only on the anterior corneal surface. Prospective validity assessment. This study was conducted at the Rotterdam Ophthalmic Institute, Rotterdam, Netherlands. The study population consisted of 91 eyes of 91 patients with monofocal, non-toric intraocular lenses (IOLs). Refractive astigmatism was measured with the ARK-530A autorefractor (Nidek, Gamagori, Japan). Anterior and total corneal astigmatism were measured with the Pentacam HR (Oculus, Wetzlar, Germany) and the Cassini (i-Optics, The Hague, Netherlands). Under the assumption that refractive astigmatism must equal total corneal astigmatism in these patients, accuracy of the corneal astigmatism measurements was defined as the vectorial difference with the refractive astigmatism, with lower vector differences denoting higher accuracy. The median refractive astigmatic magnitude was 0.84 diopter (D). The mean difference vector lengths were 0.61 D, 0.58 D, 0.49 D, and 0.45 D for Pentacam anterior, Cassini anterior, Pentacam total, and Cassini total corneal astigmatism, respectively. The mean difference vector length decreased by 0.12 and 0.13 D for Pentacam and Cassini, respectively, if the total instead of anterior corneal astigmatism was measured. These decreases were statistically significant (P < .001). With Pentacam as well as with Cassini, the accuracy of total corneal astigmatism measurements was higher than that of anterior corneal astigmatism measurements. Measuring total instead of anterior corneal astigmatism may therefore decrease the residual astigmatism in toric IOL implantation. Copyright © 2016 Elsevier Inc. All rights reserved.

  2. An analysis of the factors influencing the residual refractive astigmatism after cataract surgery with toric intraocular lenses.

    PubMed

    Savini, Giacomo; Næser, Kristian

    2015-01-13

    To investigate the influence of posterior corneal astigmatism, surgically-induced corneal astigmatism (SICA), intraocular lens (IOL) orientation, and effective lens position on the refractive outcome of toric IOLs. Five models were prospectively investigated. Keratometric astigmatism and an intended SICA of 0.2 diopters (D) were entered into model 1. Total corneal astigmatism, measured by a rotating Scheimpflug camera, was used instead of keratometric astigmatism in model 2. The mean postoperative SICA, the actual postoperative IOL orientation, and the influence of the effective lens position were added, respectively, into models 3, 4, and 5. Astigmatic data were vectorially described by meridional and torsional powers. A set of equations was developed to describe the error in refractive astigmatism (ERA) as the difference between the postoperative refractive astigmatism and the target refractive astigmatism. We enrolled 40 consecutive eyes. In model 1, ERA calculations revealed significant cylinder overcorrection in with-the-rule (WTR) eyes (meridional power = -0.59 ± 0.34 D, P < 0.0001) and undercorrection in against-the-rule (ATR) eyes (0.32 ± 0.42 D, P = 0.01). When total corneal astigmatism was used instead of keratometric astigmatism (model 2), the ERA meridional power decreased in WTR (-0.13 ± 0.42 D) and ATR (0.07 ± 0.59 D) eyes, both values being not statistically significant. Models 3 to 5 did not lead to significant improvement. Posterior corneal astigmatism exerts the highest influence on the ERA after toric IOL implantation. Basing calculations on total corneal astigmatism rather than keratometric astigmatism improves the prediction of the residual refractive astigmatism. Copyright 2015 The Association for Research in Vision and Ophthalmology, Inc.

  3. Changes in Anterior, Posterior, and Total Corneal Astigmatism after Descemet Membrane Endothelial Keratoplasty

    PubMed Central

    Zumhagen, Lars; Rosentreter, André; Eter, Nicole

    2017-01-01

    Purpose. To evaluate changes in anterior, posterior, and total corneal astigmatism in patients after Descemet membrane endothelial keratoplasty (DMEK). Methods. We retrospectively included 29 eyes of 23 patients (age 67.6 ± 9.8 years, 13 female, 10 male) after DMEK surgery. The magnitude and axis orientation of anterior, posterior, and total corneal astigmatism before and after DMEK were determined using a rotating Scheimpflug system (Pentacam HR, Oculus). Results. The magnitude of anterior, posterior, and total corneal astigmatism in the central cornea did not change significantly after surgery. Before surgery, we found a significant correlation between the magnitudes of anterior and posterior corneal astigmatism (Spearman's correlation coefficient (rS) = 0.526, P = 0.003), while after surgery this correlation was no longer significant (rS = 0.038, P = 0.843). There was a significant correlation between the vector difference between preoperative and postoperative posterior astigmatism and the change in corneal pachymetry (rP = 0.47, P = 0.010). Conclusions. Posterior corneal astigmatism (especially the orientation) and therefore the relationship between anterior and total corneal astigmatism may change after DMEK. This should be considered to improve the accuracy of toric IOL power calculations following phakic DMEK or in combined procedures. PMID:28553547

  4. Changes in Anterior, Posterior, and Total Corneal Astigmatism after Descemet Membrane Endothelial Keratoplasty.

    PubMed

    Alnawaiseh, Maged; Zumhagen, Lars; Rosentreter, André; Eter, Nicole

    2017-01-01

    Purpose. To evaluate changes in anterior, posterior, and total corneal astigmatism in patients after Descemet membrane endothelial keratoplasty (DMEK). Methods. We retrospectively included 29 eyes of 23 patients (age 67.6 ± 9.8 years, 13 female, 10 male) after DMEK surgery. The magnitude and axis orientation of anterior, posterior, and total corneal astigmatism before and after DMEK were determined using a rotating Scheimpflug system (Pentacam HR, Oculus). Results. The magnitude of anterior, posterior, and total corneal astigmatism in the central cornea did not change significantly after surgery. Before surgery, we found a significant correlation between the magnitudes of anterior and posterior corneal astigmatism (Spearman's correlation coefficient (rS) = 0.526, P = 0.003), while after surgery this correlation was no longer significant (rS = 0.038, P = 0.843). There was a significant correlation between the vector difference between preoperative and postoperative posterior astigmatism and the change in corneal pachymetry (rP = 0.47, P = 0.010). Conclusions. Posterior corneal astigmatism (especially the orientation) and therefore the relationship between anterior and total corneal astigmatism may change after DMEK. This should be considered to improve the accuracy of toric IOL power calculations following phakic DMEK or in combined procedures.

  5. A novel color-LED corneal topographer to assess astigmatism in pseudophakic eyes.

    PubMed

    Ferreira, Tiago B; Ribeiro, Filomena J

    2016-01-01

    To assess the accuracy of corneal astigmatism evaluation measured by four techniques, Orbscan IIz(®), Lenstar LS900(®), Cassini(®), and Total Cassini (anterior + posterior surface), in pseudophakic eyes. A total of 30 patients (46 eyes) who had undergone cataract surgery with the implantation of a monofocal intraocular lens (AcrySof IQ) were assessed after surgery. For each eye, subjective assessment of astigmatism and its axis was performed. Minimum, maximum, and mean keratometry and astigmatism and its axis were evaluated using the four measurement techniques. All measurements were compared with the subjective measurements. Agreement between each measurement technique and subjective assessment was evaluated using Bland-Altman plots. Linear regressions were performed and compared. Linear regression analysis of astigmatism axis showed very high R (2) for all models, with Total Cassini showing the least difference to the unit slope (0.052) and the least difference to a null constant (3.790), although not statistically different from the other models. Regarding astigmatism value, the Cassini and Total Cassini models were similar and statistically better than the Lenstar model. Cassini and Total Cassini showed better J0 compared with Orbscan. On linear regression models, Cassini and Total Cassini showed the best performance regarding astigmatism value. Cassini and Total Cassini also showed the least J0 deviation from the Cartesian origin compared with Orbscan, which had the lowest performance. Total corneal measurement with the color LED topographer seems to be a better technique for astigmatism assessment.

  6. Vector analysis of astigmatic correction after small-incision lenticule extraction and femtosecond-assisted LASIK for low to moderate myopic astigmatism.

    PubMed

    Chan, Tommy C Y; Ng, Alex L K; Cheng, George P M; Wang, Zheng; Ye, Cong; Woo, Victor C P; Tham, Clement C Y; Jhanji, Vishal

    2016-04-01

    To compare astigmatic correction between femtosecond-assisted laser in situ keratomileusis (LASIK) and small-incision lenticule extraction (SMILE). A total of 111 patients were included in this prospective study. Fifty-seven eyes were treated with LASIK and 54 eyes were treated with SMILE for myopia with low to moderate (-0.25 to -4.0 D) astigmatism. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity and manifest refraction were measured preoperatively and at 1 and 3 months postoperatively. Visual and refractive outcomes were reported. Changes in refractive astigmatism were evaluated using vector analysis. Preoperative characteristics were similar between both groups. The UDVA at 1 and 3 months was better in the LASIK group compared with the SMILE group (p<0.009). Postoperative cylinder was higher in the SMILE group (p<0.001). Fewer eyes attained the attempted cylindrical correction in the SMILE group (p<0.029). Vector analysis showed no significant difference in target-induced astigmatism (p=0.091) and angle of error (p>0.596) between the two groups. Surgically induced astigmatism was significantly lower in the SMILE group (p<0.023), while the difference vector (p<0.001) and absolute angle of error (p<0.016) were significantly higher in the SMILE group. No significant difference was found in these parameters between 1 and 3 months in both groups (p>0.122). Our results showed that SMILE offered a less favourable astigmatic correction comparable to femtosecond-assisted LASIK in eyes with low to moderate myopic astigmatism. The alignment of treatment was more variable in SMILE, leading to a lower efficacy compared with LASIK by 3 months postoperatively. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

  7. Iris-fixated toric phakic intraocular lens for myopic astigmatism.

    PubMed

    Muñoz, Gonzalo; Cardoner, Antoni; Albarrán-Diego, César; Ferrer-Blasco, Teresa; Belda-Salmerón, Lurdes

    2012-07-01

    To evaluate the efficacy, predictability, safety, stability, and complications of the Artiflex toric iris-fixated phakic intraocular lens (pIOL) for myopic astigmatism. Private practice surgery centers, Valencia and Terrassa, Spain. Cohort study. At 12 months, refraction, uncorrected (UDVA) and corrected (CDVA) distance visual acuities, complications, pIOL misalignment, and endothelial cell count (ECC) were evaluated. Indices of success and misalignment were calculated using vector analysis. The study enrolled 42 eyes in 25 patients aged 21 to 39 years. The mean spherical equivalent decreased from -8.85 diopters (D) ± 2.71 (SD) to -0.37 ± 0.46 D, with 66.7% of the eyes within ± 0.50 D. The mean cylinder power decreased from -2.90 D (range -1.50 to -5.00 D) to -0.39 D (range 0.00 to -1.50 D); refraction was highly stable. All eyes achieved a decimal UDVA of 0.5 or better and a CDVA of 0.8 or better. A gain of 1 line or more of CDVA was found in 69.1% of eyes. The mean clinical pIOL misalignment was 2.6 ± 1.8 degrees; 1 eye (2.4%) required surgical repositioning of the pIOL. The mean ECC decrease was 9.3% ± 1.8%; iris pigment precipitates were observed in 16.7% of eyes. Vector analysis showed excellent mean indices of success for overall (0.94 ± 0.04), spherical (0.96 ± 0.05), and astigmatic (0.95 ± 0.16) corrections; the mean angle of error was 1.8 ± 2.7 degrees. Implantation of the toric pIOL was effective, predictable, safe, and stable for the correction of myopic astigmatism. No author has a financial or proprietary interest in any material or method mentioned. Copyright © 2012 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  8. Variation of axial and oblique astigmatism with accommodation across the visual field

    PubMed Central

    Liu, Tao; Thibos, Larry N.

    2017-01-01

    In this study we investigated the impact of accommodation on axial and oblique astigmatism along 12 meridians of the central 30° of visual field and explored the compensation of corneal first-surface astigmatism by the remainder of the eye's optical system. Our experimental evidence revealed no systematic effect of accommodation on either axial or oblique astigmatism for two adult populations (myopic and emmetropic eyes). Although a few subjects exhibited systematic changes in axial astigmatism during accommodation, the dioptric value of these changes was much smaller than the amount of accommodation. For most subjects, axial and oblique astigmatism of the whole eye are both less than for the cornea alone, which indicates a compensatory role for internal optics at all accommodative states in both central and peripheral vision. A new method for determining the eye's optical axis based on visual field maps of oblique astigmatism revealed that, on average, the optical axis is 4.8° temporal and 0.39° superior to the foveal line-of-sight in object space, which agrees with previous results obtained by different methodologies and implies that foveal astigmatism includes a small amount of oblique astigmatism (0.06 D on average). Customized optical models of each eye revealed that oblique astigmatism of the corneal first surface is negligible along the pupillary axis for emmetropic and myopic eyes. Individual variation in the eye's optical axis is due in part to misalignment of the corneal and internal components that is consistent with tilting of the crystalline lens relative to the pupillary axis. PMID:28362902

  9. Laser in situ keratomileusis for high astigmatism in myopic and hyperopic eyes.

    PubMed

    Ivarsen, Anders; Næser, Kristian; Hjortdal, Jesper

    2013-01-01

    To evaluate outcomes after laser in situ keratomileusis (LASIK) in highly astigmatic myopic and hyperopic eyes. University eye clinic. Retrospective case series. Eyes with more than 2.0 diopters (D) of astigmatism were identified from patient records. The mean preoperative cylinder was -3.92 D ± 0.82 (SD) in myopic eyes and -4.42 ± 1.10 D in hyperopic eyes. Patients were examined preoperatively and 3 months postoperatively. Laser in situ keratomileusis was performed with a Visumax femtosecond laser and a MEL-80 excimer laser. Preoperative and postoperative refractions were converted to polar values. Induced torsion and achieved correction of sphere and cylinder were determined. After 3 months, the mean sphere was 0.48 ± 0.68 D in myopic eyes and the mean cylinder -0.97 ± 0.52 D. Spherical equivalent (SE) correction was 0.05 ± 0.42 D from target. Astigmatism was 0.77 ± 0.62 D undercorrected (P<.01), and the mean induced torsion was -0.18 ± 0.51 D (P=.02). Astigmatic undercorrection was 21% of the intended correction. In hyperopia, the mean 3-month refraction was 0.79 ± 0.83 D in sphere and -1.38 ± 0.90 D in cylinder. The SE refraction was -0.01 ± 0.71 D from target. Astigmatism was 1.17 ± 0.81 D undercorrected (P<.01), with no significant torsion. Intended and achieved astigmatic corrections were correlated, with astigmatism being 28% undercorrected. Laser in situ keratomileusis in highly astigmatic eyes precisely corrected SE refraction but led to astigmatic undercorrection, particularly in hyperopia. Little to no torsion of the cylinder axis was induced. Copyright © 2012 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  10. Accuracy of the Spot and Plusoptix photoscreeners for detection of astigmatism.

    PubMed

    Crescioni, Mabel; Miller, Joseph M; Harvey, Erin M

    2015-10-01

    To evaluate the accuracy of the Spot (V2.0.16) and Plusoptix S12 (ROC4, V6.1.4.0) photoscreeners in detecting astigmatism meeting AAPOS referral criteria in students from a population with high prevalence of astigmatism. Students attending grades 3-8 on the Tohono O'odham reservation were examined. Screening was attempted with both the Spot and Plusoptix photoscreeners. Results were compared to cycloplegic refraction. Screening attempts providing no estimate of refractive error were considered fail/refer. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for detection of refractive errors were determined using AAPOS referral criteria and receiver operating characteristic area under the curve (ROC AUC) analysis was conducted for measures of astigmatism. Agreement between screening and cycloplegic refraction measurements of astigmatism, spherical equivalent, and anisometropia were assessed using t tests and correlation analyses. A total of 209 students were included. Of the total, 116 (55%) met examination-positive criteria based on cycloplegic refraction, with 105 of those (90%) meeting the criterion for astigmatism. Measurements success rates were 97% for Spot and 54% for Plusoptix. Comparing the Spot and the Plusoptix, sensitivity was 96% versus 100%, specificity was 87% versus 61%, PPV was 90% versus 76%, and NPV was 94% versus 100% for detection of refractive error. Both screeners overestimated astigmatism by 1/3 D to 2/3 D. AUC for astigmatism was 0.97 for Spot and 0.83 for Plusoptix. In this highly astigmatic population, the Spot and the Plusoptix had similar sensitivity, but the Spot had better specificity and measurement success rates. Compared with results from study samples with lower rates of astigmatism, our results highlight the need to assess the ability of screening instruments to detect individual types of refractive errors. Copyright © 2015 American Association for Pediatric Ophthalmology and Strabismus

  11. Variation of axial and oblique astigmatism with accommodation across the visual field.

    PubMed

    Liu, Tao; Thibos, Larry N

    2017-03-01

    In this study we investigated the impact of accommodation on axial and oblique astigmatism along 12 meridians of the central 30° of visual field and explored the compensation of corneal first-surface astigmatism by the remainder of the eye's optical system. Our experimental evidence revealed no systematic effect of accommodation on either axial or oblique astigmatism for two adult populations (myopic and emmetropic eyes). Although a few subjects exhibited systematic changes in axial astigmatism during accommodation, the dioptric value of these changes was much smaller than the amount of accommodation. For most subjects, axial and oblique astigmatism of the whole eye are both less than for the cornea alone, which indicates a compensatory role for internal optics at all accommodative states in both central and peripheral vision. A new method for determining the eye's optical axis based on visual field maps of oblique astigmatism revealed that, on average, the optical axis is 4.8° temporal and 0.39° superior to the foveal line-of-sight in object space, which agrees with previous results obtained by different methodologies and implies that foveal astigmatism includes a small amount of oblique astigmatism (0.06 D on average). Customized optical models of each eye revealed that oblique astigmatism of the corneal first surface is negligible along the pupillary axis for emmetropic and myopic eyes. Individual variation in the eye's optical axis is due in part to misalignment of the corneal and internal components that is consistent with tilting of the crystalline lens relative to the pupillary axis.

  12. Optical analysis for simplified astigmatic correction of non-imaging focusing heliostat

    SciTech Connect

    Chong, K.K.

    2010-08-15

    In the previous work, non-imaging focusing heliostat that consists of m x n facet mirrors can carry out continuous astigmatic correction during sun-tracking with the use of only (m + n - 2) controllers. For this paper, a simplified astigmatic correction of non-imaging focusing heliostat is proposed for reducing the number of controllers from (m + n - 2) to only two. Furthermore, a detailed optical analysis of the new proposal has been carried out and the simulated result has shown that the two-controller system can perform comparably well in astigmatic correction with a much simpler and more cost effective design. (author)

  13. Risk Factors for Astigmatism in the Vision in Preschoolers (VIP) Study

    PubMed Central

    Huang, Jiayan; Maguire, Maureen G.; Ciner, Elise; Kulp, Marjean Taylor; Cyert, Lynn A.; Quinn, Graham E.; Orel-Bixler, Deborah; Moore, Bruce; Ying, Gui-Shuang

    2014-01-01

    Purpose To determine demographic and refractive risk factors for astigmatism in the Vision in Preschoolers (VIP) Study. Methods Three- to 5-year old Head Start preschoolers (N=4,040) from 5 clinical centers underwent comprehensive eye examinations by study-certified optometrists and ophthalmologists, including monocular visual acuity (VA) testing, cover testing, and cycloplegic retinoscopy. Astigmatism was defined as the presence of ≥ +1.5 diopters (D) cylinder in either eye, measured with cycloplegic refraction. The associations of risk factors with astigmatism were evaluated using the odds ratio (OR) and its 95% confidence intervals (95% CI) from logistic regression models. Results Among 4,040 VIP Study participants over-representing children with vision disorders, 687 (17%) had astigmatism, and majority of astigmatism was with-the-rule (83.8%). In multivariate analyses, African-American (OR=1.65, 95% CI: 1.22–2.24), Hispanic (OR=2.25, 95% CI: 1.62–3.12) and Asian children (OR=1.76, 95% CI: 1.06–2.93) were more likely to have astigmatism compared with non-Hispanic white children, while American Indian children were less likely to have astigmatism than Hispanic, African American and Asian children (P<0.0001). Refractive error was associated with astigmatism in a non-linear manner, with an OR of 4.50 (95% CI: 3.00 – 6.76) for myopia (≤ −1.0D in spherical equivalent), and 1.55 (95% CI: 1.29 –1.86) for hyperopia (≥ +2.0D) when compared to children without refractive error (> −1.0D, < +2.0D). There was a trend of an increasing percentage of astigmatism among older children (linear trend p=0.06). The analysis for risk factors of with-the-rule astigmatism provided similar results. Conclusions Among Head Start preschoolers, Hispanic ethnicity, African-American and Asian race, myopic and hyperopic refractive error were associated with an increased risk of astigmatism, consistent with findings from the population-based Multi-ethnic Pediatric Eye Disease

  14. Experimental validation of a novel imaging scheme to eliminate astigmatism

    NASA Astrophysics Data System (ADS)

    Fierroz, S.; Bitter, M.; Delgado-Aparicio, L.; Hill, K. W.; Pablant, N.; Scott, S.; Scotti, F.; Rice, J. E.

    2010-11-01

    Recent papers by Bitter et al.^1-3 have proposed novel imaging schemes to eliminate astigmatism by matched pairs of spherically bent crystals or reflectors. These imaging schemes should allow stigmatic (or point-to point) imaging at arbitrarily large angles of incidence and be applicable to a broad spectrum of the electromagnetic radiation, including microwaves, visible light, EUV radiation, and x-rays, if appropriate spherically bent reflectors are used. This paper presents experimental results from tests of one of these imaging schemes with visible light, which validate the concept of this scheme and show that stigmatic imaging of objects with areas of about 5 mm x 5 mm is possible. ^1M. Bitter et al, Rev Sci. Instrum. 79, 10E927 (2008); ^2M. Bitter et al., J. Xray Sci. Technol. 17, 153 (2009); ^3M. Bitter et al., J. Phys. B: At. Mol. Opt. Phys. 43, 144011 (2010)

  15. Proximity- and Astigmatism-Tolerant Testsites For Electrical Linewidth Measurement

    NASA Astrophysics Data System (ADS)

    Lin, Burn J.

    1989-07-01

    Electrical linewidth measurement is well-known for high precision and throughput. However, the standard four-point probe testsite is only useful for measuring the width of an isolated conducting line. Line-and-space and isolated spaces can be simulated satisfactorily by adding dummy lines parallel to the active line but weak links or potential electrical shorting situations often prematurely cause these structures to fail before their true limits are reached. In this paper, fully wrapped proximity- and astigmatism-tolerant designs for line-and-space and isolated spaces are shown. They have been successfully demonstrated with printed images. An application in evaluating the exposure-defocus window of a one-layer i-line resist using the proximity-tolerant testsites is given.

  16. On astigmatism of multi-beam optical stress sensor mounted at large incident angle

    NASA Astrophysics Data System (ADS)

    Jiang, Jinbo; Hwang, Heedon; Lee, Hak Sun; Kim, Byongju; Bong, Kee; Yoon, Euijoon

    2004-01-01

    When multi-beam optical stress sensor (MOSS) system is mounted at a large incident angle ( α), despite an improvement of the resolution in the measurements, it also induces optical astigmatism in the spot images on a charge-coupled device. During epitaxial growth, as the film stress increases, the astigmatism may result in the beam deflection changing at different rates in the directions parallel and perpendicular to the incident plane, if the α is large. In this paper, the system error due to the astigmatism is analyzed by the ray-tracing method and its predictions are compared with the experimental results. It is demonstrated here, how the spot spacing changes along the above mentioned orthogonal directions can be considered separately to minimize the error due to astigmatism in the MOSS measurements at any large α.

  17. On astigmatism of multi-beam optical stress sensor mounted at large incident angle

    NASA Astrophysics Data System (ADS)

    Jiang, Jinbo; Kee, Bong

    When multi-beam optical stress sensor (MOSS) system is mounted at a large incident angle ([alpha]), despite an improvement of the resolution in the measurements, it also induces optical astigmatism in the spot images on a charge coupled device (CCD). During epitaxial growth, as the film stress increases, the astigmatism may result in the spot spacing deflection ([delta]d) changing at different rates in the directions parallel and perpendicular to the incident plane, if the [alpha] is large. In this paper, the system error due to the astigmatism is analyzed by the ray tracing method and its predictions are compared with the the experimental results. It is demonstrated here, how the spot spacing deflections along the above mentioned orthogonal directions can be considered separately to minimize the error due to astigmatism in the MOSS measurements at any large [alpha].

  18. Astigmatism correction of a non-imaging double spectrometer fitted with a 2D array detector

    SciTech Connect

    Yaney, P.P.; Ernst, S.L.; Blackshire, J.

    1992-12-01

    A SPEX 1401 double spectrometer was adapted for a liquid nitrogen cooled CCD detector to permit both spectral and spatial analysis of ceramic specimens in a laser Raman microprobe system. The exit image of the spectrometer suffers from astigmatism due to off-axis spherical mirrors. A cylindrical lens was added before the CCD to correct for the astigmatism. The spectrometer and several lenses were modeled using an optical ray tracing program to characterize the astigmatism and to optimize the locations of the lens and the detector. The astigmatism and the spot pattern sizes determined by the model were in good agreement with he observed performance of the modified spectrometer-detector system. Typical spot patterns fell within the 23 {mu}m square pixel size.

  19. Structure of the far-field radiation in a laser with an astigmatic unstable cavity

    SciTech Connect

    Trusov, K.K. )

    1990-06-01

    The angular-distribution structure of the radiation for a laser with an astigmatic unstable telescopic cavity has been experimentally investigated, using a flash-lamp-pumped dye laser. Simple astigmatism was introduced into the cavity with a weak lens tilted with respect to the cavity axis, and the range of astigmatism variation was 10{sup {minus}3} to 5 {times} 10{sup {minus}1} wave. An optical scheme has been proposed for the experiments that permits adequate simulation of the beam structure of the real laser by means of probe radiation introduced into the passive cavity. Comparative experiments in the regimes of active and passive cavities have shown that no fewer than two cavity modes of different order form the angular structure of the astigmatic cavity radiation.

  20. Clinical evaluation of keratometry and computerised videokeratography: intraobserver and interobserver variability on normal and astigmatic corneas

    PubMed Central

    Karabatsas, C.; Cook, S.; Papaefthymiou, J.; Turner, P.; Sparrow, J.

    1998-01-01

    AIMS—To evaluate intra- and interobserver variability in measurements on normal and astigmatic corneas with keratometry and computerised videokeratography.
METHODS—Keratometric readings with the 10 SL/O Zeiss keratometer and topographic maps with the TMS-1 were obtained by two independent examiners on 32 normal and 33 postkeratoplasty corneas. Inter- and intraobserver coefficients of variability (COR) for measurements of steep and flat meridian power and location, in addition to the magnitude of astigmatism, were assessed.
RESULTS—Compared with TMS-1, the 10 SL/O keratometer showed a superior repeatability in measuring normal corneas (intraobserver COR for keratometry and TMS-1 respectively: 0.22 and 0.30 D for steep meridian power; 0.18 and 0.44 D for flat meridian power; 0.26 and 0.40 D for astigmatism; 5° and 26° for steep meridian location; 5° and 13° for flat meridian location). Astigmatism intraobserver COR (0.20 D and 0.26 D for the two observers) and interobserver COR (0.28 D) of the keratometer for normal corneas was very good and not affected by observers' experience. Repeatability of the TMS-1 on normal corneas was found to be: (a) observer related, and (b) astigmatism related. A novice observer showed a much greater COR (1.62 D for astigmatism, 30° for flat meridian location) compared with the experienced examiner (0.40 D for astigmatism, 13° for flat meridian location). Higher deviation scores were observed for corneas with higher astigmatism. For the postkeratoplasty corneas, again the keratometer achieved superior reproducibility (astigmatism interobserver COR 1.12 D for keratometry, 4.06 D for TMS-1; steep meridian location interobserver COR 10° for keratometry, 34° for TMS-1).
CONCLUSION—Keratometric readings are more reproducible than topographic data both for normal and postkeratoplasty corneas. The two instruments should not be used interchangeably especially on highly astigmatic corneas. For the TMS-1

  1. Three-dimensional location of micrometer-sized particles in macroscopic domains using astigmatic aberrations.

    PubMed

    Fuchs, Thomas; Hain, Rainer; Kähler, Christian J

    2014-03-01

    This Letter presents a theoretical and experimental image formation study in the presence of astigmatic aberrations. A three-dimensional, macroscopic location scheme of micrometer-sized particles for the single camera astigmatism particle tracking velocimetry (APTV) technique is introduced. Average particle z position determination errors of the technique are as low as 0.33%, with a measurement depth of 40 mm. These accuracies show APTV's ability of measuring volumetric velocity fields in macroscopic domains with limited optical access.

  2. Comparison of Astigmatism Induced by Combined Inferior Oblique Anterior Transposition Procedure and Lateral Rectus Recession Alone

    PubMed Central

    Eum, Sun Jung

    2016-01-01

    Purpose The purpose of this study is to compare the magnitude and axis of astigmatism induced by a combined inferior oblique (IO) anterior transposition procedure with lateral rectus (LR) recession versus LR recession alone. Methods Forty-six patients were retrospectively analyzed. The subjects were divided into two groups: those having concurrent inferior oblique muscle overaction (IOOA) and intermittent exotropia (group 1, 20 patients) and those having only intermittent exotropia as a control (group 2, 26 patients). Group 1 underwent combined anterior transposition of IO with LR recession and group 2 underwent LR recession alone. Induced astigmatism was defined as the difference between preoperative and postoperative astigmatism using double-angle vector analysis. Cylinder power, axis of induced astigmatism, and spherical equivalent were analyzed at 1 week, 1 month, and 3 months after surgery. Results Larger changes in the axis of induced astigmatism were observed in group 1, with 4.5° incyclotorsion, than in group 2 at 1 week after surgery (axis, 84.5° vs. 91°; p < 0.001). However, there was no statistically significant inter-group difference thereafter. Relaxation and rapid regression in the incyclotorsion of induced astigmatism were observed over-time. Spherical equivalent significantly decreased postoperatively at 1 month in both groups, indicating a myopic shift (p = 0.011 for group 1 and p = 0.019 for group 2) but did not show significant differences at 3 months after surgery (p = 0.107 for group 1 and p = 0.760 for group 2). Conclusions Combined IO anterior transposition procedures caused an increased change in the axis of induced astigmatism, including temporary incyclotorsion, during the first week after surgery. However, this significant difference was not maintained thereafter. Thus, combined IO surgery with LR recession does not seem to produce a sustained astigmatic change, which can be a potential risk factor of postoperative amblyopia or

  3. Optical image reconstruction using an astigmatic lens for synthetic-aperture imaging ladar

    NASA Astrophysics Data System (ADS)

    Sun, Zhiwei; Hou, Peipei; Zhi, Yanan; Sun, Jianfeng; Zhou, Yu; Xu, Qian; Liu, Liren

    2014-11-01

    An optical processor for synthetic-aperture imaging ladar (SAIL) utilizing one astigmatic lens is proposed. The processor comprises two structures of transmitting and reflecting. The imaging process is mathematically analyzed using the unified data-collection equation of side-looking and down-looking SAILs. Results show that the astigmatic lens can be replaced with a cylindrical lens on certain conditions. To verify this concept, laboratory experiment is conducted, the imaging result of data collected from one SAIL demonstrator is given.

  4. The Effect of the Degree of Astigmatism on Optical Quality in Children.

    PubMed

    Gao, Jing; Wang, Xiao-Xia; Wang, Lin; Sun, Yuan; Liu, Rui-Fen; Zhao, Qi

    2017-01-01

    To investigate the effect of the degree of astigmatism on optical quality in children. The important objective evaluation parameters we focus on include the RMS of the high-order aberrations, MTF, and PSF. The children, age ranging from 7 to 10 years old, underwent an optometry examination. Fifty-nine children who met the inclusion criteria were divided into three groups: A (1.0 D ≤ astigmatism < 2.0 D), B (2.0 D ≤ astigmatism < 3.0 D), and C (3.0 D ≤ astigmatism < 4.0 D). The OPD-SCAN-III aberrometer was used to measure PSF, MTF, and other optical parameters. Total higher-order aberrations, total coma aberrations, total spherical aberrations, and total trefoil aberrations corresponding to the RMS value, the AR value of MTF, and the SR value of PSF with a 4 mm pupil diameter were assessed. RMS-HO, RMS-T.Coma, RMS-T.Tre, and RMS-T.Sph in the three groups were significantly increased with increasing the degree of astigmatism, while there were no significant differences in RMS-T.Sph between the groups. The AR value and the SR value decreased with increasing degree of astigmatism, and there were significant differences in the AR value and the SR value. Astigmatism has a significant influence on the higher-order aberrations, MTF, and PSF in the children. The effect of astigmatism value on the optical quality is mainly reflected in the change in these three parameters.

  5. The Effect of the Degree of Astigmatism on Optical Quality in Children

    PubMed Central

    Wang, Lin; Liu, Rui-fen

    2017-01-01

    Purpose To investigate the effect of the degree of astigmatism on optical quality in children. The important objective evaluation parameters we focus on include the RMS of the high-order aberrations, MTF, and PSF. Methods The children, age ranging from 7 to 10 years old, underwent an optometry examination. Fifty-nine children who met the inclusion criteria were divided into three groups: A (1.0 D ≤ astigmatism < 2.0 D), B (2.0 D ≤ astigmatism < 3.0 D), and C (3.0 D ≤ astigmatism < 4.0 D). The OPD-SCAN-III aberrometer was used to measure PSF, MTF, and other optical parameters. Total higher-order aberrations, total coma aberrations, total spherical aberrations, and total trefoil aberrations corresponding to the RMS value, the AR value of MTF, and the SR value of PSF with a 4 mm pupil diameter were assessed. Results RMS-HO, RMS-T.Coma, RMS-T.Tre, and RMS-T.Sph in the three groups were significantly increased with increasing the degree of astigmatism, while there were no significant differences in RMS-T.Sph between the groups. The AR value and the SR value decreased with increasing degree of astigmatism, and there were significant differences in the AR value and the SR value. Conclusion Astigmatism has a significant influence on the higher-order aberrations, MTF, and PSF in the children. The effect of astigmatism value on the optical quality is mainly reflected in the change in these three parameters. PMID:28656103

  6. Comparison of Astigmatism Induced by Combined Inferior Oblique Anterior Transposition Procedure and Lateral Rectus Recession Alone.

    PubMed

    Eum, Sun Jung; Chun, Bo Young

    2016-12-01

    The purpose of this study is to compare the magnitude and axis of astigmatism induced by a combined inferior oblique (IO) anterior transposition procedure with lateral rectus (LR) recession versus LR recession alone. Forty-six patients were retrospectively analyzed. The subjects were divided into two groups: those having concurrent inferior oblique muscle overaction (IOOA) and intermittent exotropia (group 1, 20 patients) and those having only intermittent exotropia as a control (group 2, 26 patients). Group 1 underwent combined anterior transposition of IO with LR recession and group 2 underwent LR recession alone. Induced astigmatism was defined as the difference between preoperative and postoperative astigmatism using double-angle vector analysis. Cylinder power, axis of induced astigmatism, and spherical equivalent were analyzed at 1 week, 1 month, and 3 months after surgery. Larger changes in the axis of induced astigmatism were observed in group 1, with 4.5° incyclotorsion, than in group 2 at 1 week after surgery (axis, 84.5° vs. 91°; p < 0.001). However, there was no statistically significant inter-group difference thereafter. Relaxation and rapid regression in the incyclotorsion of induced astigmatism were observed over-time. Spherical equivalent significantly decreased postoperatively at 1 month in both groups, indicating a myopic shift (p = 0.011 for group 1 and p = 0.019 for group 2) but did not show significant differences at 3 months after surgery (p = 0.107 for group 1 and p = 0.760 for group 2). Combined IO anterior transposition procedures caused an increased change in the axis of induced astigmatism, including temporary incyclotorsion, during the first week after surgery. However, this significant difference was not maintained thereafter. Thus, combined IO surgery with LR recession does not seem to produce a sustained astigmatic change, which can be a potential risk factor of postoperative amblyopia or diplopia compared with LR recession alone.

  7. Vector Analysis of Corneal Astigmatism After Combined Femtosecond-Assisted Phacoemulsification and Arcuate Keratotomy.

    PubMed

    Chan, Tommy C Y; Cheng, George P M; Wang, Zheng; Tham, Clement C Y; Woo, Victor C P; Jhanji, Vishal

    2015-08-01

    To evaluate the outcomes of femtosecond-assisted arcuate keratotomy combined with cataract surgery in eyes with low to moderate corneal astigmatism. Retrospective, interventional case series. This study included patients who underwent combined femtosecond-assisted phacoemulsification and arcuate keratotomy between March 2013 and August 2013. Keratometric astigmatism was evaluated before and 2 months after the surgery. Vector analysis of the astigmatic changes was performed using the Alpins method. Overall, 54 eyes of 54 patients (18 male and 36 female; mean age, 68.8 ± 11.4 years) were included. The mean preoperative (target-induced astigmatism) and postoperative astigmatism was 1.33 ± 0.57 diopters (D) and 0.87 ± 0.56 D, respectively (P < .001). The magnitude of error (difference between surgically induced and target-induced astigmatism) (-0.13 ± 0.68 D), as well as the correction index (ratio of surgically induced and target-induced astigmatism) (0.86 ± 0.52), demonstrated slight undercorrection. The angle of error was very close to 0, indicating no significant systematic error of misaligned treatment. However, the absolute angle of error showed a less favorable range (17.5 ± 19.2 degrees), suggesting variable factors such as healing or alignment at an individual level. There were no intraoperative or postoperative complications. Combined phacoemulsification with arcuate keratotomy using femtosecond laser appears to be a relatively easy and safe means for management of low to moderate corneal astigmatism in cataract surgery candidates. Misalignment at an individual level can reduce its effectiveness. This issue remains to be elucidated in future studies. Copyright © 2015 Elsevier Inc. All rights reserved.

  8. Comparison of astigmatism correction using either peripheral corneal relaxing incisions or toric intraocular lenses.

    PubMed

    Muftuoglu, Ilkay Kilic; Aydin Akova, Yonca; Aksoy, Sibel; Unsal, Erkan

    2016-01-01

    To compare the efficacy and short-term stability of toric intraocular lenses (tIOL) and peripheral cornea relaxing incisions (PCRI) during phacoemulsification. Patients with preexisting corneal astigmatism had cataract surgery either with tIOL (AcrySof Toric) (39 eyes of 35 patients) or standard intraocular lens (AcrySof) + PCRIs (38 eyes of 33 patients). Patients were retrospectively evaluated for manifest refraction, corneal topography, and uncorrected and corrected visual acuities preoperatively and at postoperative 1 and 6 months. The Alpins vectorial method was used to analyze the target induced astigmatism (TIA) and surgically induced astigmatism (SIA), magnitude of error (the difference between the magnitude of SIA and TIA) (ME), and correction index. Mean preoperative corneal astigmatism was 2.21 ± 1.32 D in the tIOL group and 2.24 ± 0.96 D in the PCRI group; the difference was not significant. The decrease in astigmatism was significant in both groups at last follow-up (64% tIOL group, 32% PCRI group, p<0.01, Wilcoxon signed rank test). The mean remaining refractive astigmatism was significantly higher in the PCRI group than in the tIOL group at 1-month (1.42 ± 1.22, 0.89 ± 0.68, respectively) and 6-month follow-ups (1.75 ± 1.37 D, 0.92 ± 0.72, respectively) (p<0.01). The mean ME was significantly lower (-0.35 versus -0.88) with a higher correction index (0.96 versus 0.56) in the tIOL group at 6 months postoperatively. Both tIOL implantation and using PCRI were effective methods to reduce preoperative astigmatism at the time of the cataract surgery. However, tIOLs provided better remaining astigmatism with a more stable refraction than PCRI.

  9. Onset and Progression of With-the-Rule Astigmatism in Children with Infantile Nystagmus Syndrome

    PubMed Central

    Wyatt, Lauren M.; Felius, Joost; Stager, David R.; Stager, David R.; Birch, Eileen E.; Bedell, Harold E.

    2010-01-01

    Purpose. The purpose of this study was to examine the onset and progression of with-the-rule (WTR) astigmatism during the first 8 years of life in children with idiopathic infantile nystagmus syndrome (INS) or INS associated with albinism and to compare their development with that of normal children. Also explored was whether early WTR astigmatism influences emmetropization in children with INS and whether there is evidence of meridional emmetropization. Methods. Cycloplegic refractions culled from medical records were converted into power vector components: M (spherical equivalent), J0 (positive J0 indicates WTR astigmatism), and J45 (oblique astigmatism). Two diagnostic groups (idiopathic, n = 106; albinism, n = 95) were evaluated and compared with a reference normal group (n = 495). Four age subgroups were evaluated: age≤0.5 year, 0.5astigmatism was prevalent among children with INS, even during infancy. Both the prevalence and magnitude of WTR astigmatism increased with age in both INS groups. Predicted J0 from the fitted longitudinal data agreed with cross-sectional data. Moreover, the spherical equivalent of children with INS demonstrated little emmetropization during the first 8 years of life. Conclusions. Both the cross-sectional and longitudinal data showed that WTR astigmatism was common among children with INS and increased in magnitude with age during the first 8 years of life. Changes observed in meridional refractive error with age were consistent with meridional emmetropization in children with INS and WTR astigmatism. PMID:20019374

  10. Calculations of actual corneal astigmatism using total corneal refractive power before and after myopic keratorefractive surgery

    PubMed Central

    Seo, Kyoung Yul; Yang, Hun; Kim, Wook Kyum; Nam, Sang Min

    2017-01-01

    Purpose To calculate actual corneal astigmatism using the total corneal refractive astigmatism for the 4-mm apex zone of the Pentacam (TCRP4astig) and keratometric astigmatism (Kastig) before and after photorefractive keratectomy or laser in situ keratomileusis Methods Uncomplicated 56 eyes after more than 6 months from the surgery were recruited by chart review. Various corneal astigmatisms were measured using the Pentacam and autokeratometer before and after surgery. Three eyes were excluded and 53 eyes of 38 subjects with with-the-rule astigmatism (WTR) were finally included. The astigmatisms were investigated using polar value analysis. When TCRP4astig was set as an actual astigmatism, the efficacy of arithmetic or coefficient adjustment of Kastig was evaluated using bivariate analysis. Results The difference between the simulated keratometer astigmatism of the Pentacam (SimKastig) and Kastig was strongly correlated with the difference between TCRP4astig and Kastig. TCRP4astig was different from Kastig in magnitude rather than meridian before and after surgery; the preoperative difference was due to the posterior cornea only; however, the postoperative difference was observed in both anterior and posterior parts. For arithmetic adjustment, 0.28 D and 0.27 D were subtracted from the preoperative and postoperative magnitudes of Kastig, respectively. For coefficient adjustment, the preoperative and postoperative magnitudes of Kastig were multiplied by 0.80 and 0.66, respectively. By arithmetic or coefficient adjustment, the difference between TCRP4astig and adjusted Kastig would be less than 0.75 D in magnitude for 95% of cases. Conclusions Kastig was successfully adjusted to TCPR4astig before and after myopic keratorefractive surgery in cases of WTR. For use of TCRP4astig directly, SimKastig and Kastig should be matched. PMID:28403194

  11. Calculations of actual corneal astigmatism using total corneal refractive power before and after myopic keratorefractive surgery.

    PubMed

    Seo, Kyoung Yul; Yang, Hun; Kim, Wook Kyum; Nam, Sang Min

    2017-01-01

    To calculate actual corneal astigmatism using the total corneal refractive astigmatism for the 4-mm apex zone of the Pentacam (TCRP4astig) and keratometric astigmatism (Kastig) before and after photorefractive keratectomy or laser in situ keratomileusis. Uncomplicated 56 eyes after more than 6 months from the surgery were recruited by chart review. Various corneal astigmatisms were measured using the Pentacam and autokeratometer before and after surgery. Three eyes were excluded and 53 eyes of 38 subjects with with-the-rule astigmatism (WTR) were finally included. The astigmatisms were investigated using polar value analysis. When TCRP4astig was set as an actual astigmatism, the efficacy of arithmetic or coefficient adjustment of Kastig was evaluated using bivariate analysis. The difference between the simulated keratometer astigmatism of the Pentacam (SimKastig) and Kastig was strongly correlated with the difference between TCRP4astig and Kastig. TCRP4astig was different from Kastig in magnitude rather than meridian before and after surgery; the preoperative difference was due to the posterior cornea only; however, the postoperative difference was observed in both anterior and posterior parts. For arithmetic adjustment, 0.28 D and 0.27 D were subtracted from the preoperative and postoperative magnitudes of Kastig, respectively. For coefficient adjustment, the preoperative and postoperative magnitudes of Kastig were multiplied by 0.80 and 0.66, respectively. By arithmetic or coefficient adjustment, the difference between TCRP4astig and adjusted Kastig would be less than 0.75 D in magnitude for 95% of cases. Kastig was successfully adjusted to TCPR4astig before and after myopic keratorefractive surgery in cases of WTR. For use of TCRP4astig directly, SimKastig and Kastig should be matched.

  12. Distribution of the anterior, posterior, and total corneal astigmatism in healthy eyes.

    PubMed

    Feizi, Sepehr; Naderan, Mohammad; Ownagh, Vahid; Sadeghpour, Fatemeh

    2017-03-13

    To evaluate the magnitude and axis orientation of the anterior, posterior, and total corneal astigmatism in normal healthy eyes of an Iranian population. In a prospective cross-sectional study, ophthalmic and anterior segment parameters of 153 healthy eyes of 153 subjects were evaluated by Galilei dual Scheimpflug analyzer. The magnitude and axis orientation [with-the-rule (WTR), against-the-rule (ATR), and oblique] of the anterior, posterior, and total corneal astigmatism measurements (ACA, PCA, and TCA) were compared according to the age, sex, and other ophthalmic parameters. The mean ± SD age of the study population was 30 ± 5.9 years. The mean magnitude was 1.09 ± 0.76 diopters (D) for ACA, 0.30 ± 0.13 D for PCA, and 1.08 ± 0.77 D for TCA. Males had a significantly higher magnitude of PCA than females (p = 0.041). Most eyes had a WTR anterior astigmatism and an ATR posterior astigmatism. The WTR astigmatism had a higher mean magnitude compared to the ATR and oblique astigmatism in all the astigmatism groups, with a significant difference in the ACA and TCA groups (p < 0.05). PCA magnitude exceeded 0.50 D in only 7.8% of the subjects. ACA, PCA, and TCA were significantly correlated with each other and also had a significant correlation with the anterior and posterior maximum corneal elevation measurements (p < 0.001). The results of this study although are limited due to the small number of participants and confined to our demographics, provided information regarding a population that was not described before and may be helpful in obtaining optimum results in astigmatism correction in refractive surgery or designing new intraocular lenses.

  13. The efficacy of a single continuous nylon suture for control of post keratoplasty astigmatism.

    PubMed Central

    Van Meter, W

    1996-01-01

    PURPOSE: Post operative adjustment of a single continuous suture is an effective means of reducing post keratoplasty astigmatism. This study evaluates post keratoplasty keratometry following suture adjustment with an adjusted suture in place and after the suture is removed. METHODS: Average keratometric astigmatism was measured over 24 months time in 26 patients with an adjusted continuous suture and 24 patients with a continuous suture that was not adjusted. Average keratometry in 43 patients with an adjusted continuous suture was compared with 37 patients with combined continuous and interrupted sutures. Finally, suture out astigmatism in 19 adjusted patients was compared to six patients with no adjustment. RESULTS: There was an increase in average corneal astigmatism over two years of 2.2 diopters in the adjusted group and 1.7 diopters in the non-adjusted group with sutures in place. One year following surgery, average keratometry flattened from 47.5 to 42.9 diopters in the adjusted continuous group and from 47.0 to 46.0 diopters in the group with combined continuous and interrupted sutures. Following suture removal, average astigmatism in patients who had suture adjustment was 4.4 diopters +/- 2.5 diopters (range 1-10 diopters), and 6.01 diopters (range 4-7) in the non-adjusted group. CONCLUSIONS: Average post keratoplasty astigmatism increases after a continuous suture is adjusted but the increase is comparable to patients with acceptable astigmatism who do not require adjustment. More progressive corneal flattening over 12 months time is seen with a continuous suture than which combined sutures. Average suture out astigmatism was 4.0 diopters following suture adjustment, compared to an average of 8.4 diopters prior to adjustment. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 7A FIGURE 7B PMID:8981721

  14. Prevalence of Corneal Astigmatism in an NHS Cataract Surgery Practice in Northern Ireland

    PubMed Central

    Hassett, Patrick

    2017-01-01

    PURPOSE Post-operative corneal astigmatism following cataract surgery can leave the patient with visual impairment. Correcting it at the time of surgery with a toric intraocular lens (TIOL) can give patients a better final visual outcome. The purpose was to determine the prevalence of corneal astigmatism in a cataract population and assess the demand for TIOL. METHODS Keratometric data was collected and analyzed for all patients who attended for routine cataract surgery under the care of a single surgeon based in Altnagelvin Area Hospital, Northern Ireland (NI). All patients were included between January 2008 and December 2014. Data was collected retrospectively for this observational study. RESULTS There were 2080 consecutive eyes of 1788 patients. The mean corneal astigmatism was 1.09 ± 0.83. Corneal astigmatism was 1.50D or less in 1621 eyes (78%). It was more than 2.00 D in 242 eyes (11.6%), more than 2.50 D in 127 eyes (6.1%), more than 3.00D in 68 eyes (3.27%) and more than 3.50 D in 45 eyes (2.16%). CONCLUSION For routine cataract surgery, 41.3% of eyes had more than 1.00 D of corneal astigmatism and 11.6% had more and 2.00D. Females had more astigmatism than males. This shows the potential demand for the TIOL in this population.

  15. Minimizing surgically induced astigmatism at the time of cataract surgery using a square posterior limbal incision.

    PubMed

    Ernest, Paul; Hill, Warren; Potvin, Richard

    2011-01-01

    Purpose. To compare the surgically induced astigmatism from clear corneal and square posterior limbal incisions at the time of cataract surgery. Methods. Surgically induced astigmatism was calculated for a set of eyes after cataract surgery using a temporal 2.2 mm square posterior limbal incision. Results were compared to similar available data from surgeons using clear corneal incisions of similar size. Results. Preoperative corneal astigmatism averaged 1.0 D and was not significantly different between the incision types. Surgically induced astigmatism with the 2.2 mm posterior limbal incision averaged 0.25 ± 0.14 D, significantly lower in magnitude than the aggregate surgically induced astigmatism produced by the 2.2 mm clear corneal incision (0.68 ± 0.49 D). Conclusion. The 2.2 mm square posterior limbal incision induced significantly less, and significantly less variable, surgically induced astigmatism relative to a similar-sized clear corneal incision. This is likely to improve refractive outcomes, particularly important with regard to premium intraocular lenses.

  16. A simple method for astigmatic compensation of folded resonator without Brewster window.

    PubMed

    Qiao, Wen; Xiaojun, Zhang; Yonggang, Wang; Liqun, Sun; Hanben, Niu

    2014-02-10

    A folded resonator requires an oblique angle of incidence on the folded curved mirror, which introduces astigmatic distortions that limit the performance of the lasers. We present a simple method to compensate the astigmatism of folded resonator without Brewster windows for the first time to the best of our knowledge. Based on the theory of the propagation and transformation of Gaussian beams, the method is both effective and reliable. Theoretical results show that the folded resonator can be compensated astigmatism completely when the following two conditions are fulfilled. Firstly, when the Gaussian beam with a determined size beam waist is obliquely incident on an off-axis concave mirror, two new Gaussian beam respectively in the tangential and sagittal planes are formed. Another off-axis concave mirror is located at another intersection point of the two new Gaussian beams. Secondly, adjusting the incident angle of the second concave mirror or its focal length can make the above two Gaussian beam coincide in the image plane of the second concave mirror, which compensates the astigmatic aberration completely. A side-pumped continues-wave (CW) passively mode locked Nd:YAG laser was taken as an example of the astigmatically compensated folded resonators. The experimental results show good agreement with the theoretical predictions. This method can be used effectively to design astigmatically compensated cavities resonator of high-performance lasers.

  17. Comparison of Surgically Induced Astigmatisms after Clear Corneal Incisions of Different Sizes

    PubMed Central

    Mohamed, Tarek; Fine, I. Howard

    2007-01-01

    Purpose This study was performed to assess efficiency and stability of astigmatic change by incision size after cataract surgery. Methods This work was designed as a retrospective, comparative, nonrandomized interventional study. A total of 121 cases of cataract surgery were reviewed in 98 patients performed by one surgeon at the Oregon Eye Institute in Eugene, OR, USA with 3-year follow-ups. All procedures were performed with the temporal approach of self-sealing incisions. The serial change in surgically induced astigmatisms were examined in all cases of three groups: Group A, cartridge injection of a foldable IOL through a 2.5 mm self-sealing incision; Group B, cartridge injection of a foldable IOL through a 3.0 mm self-sealing incision; Group C, cartridge injection of a foldable IOL through a 3.5 mm self-sealing incision. Keratometric data were obtained reoperatively, and 3 weeks, 3 months, 6 months, 9 months, 12 months, 24 months and 36 months postoperatively. Polar value analysis was performed to calculate the surgically induced astigmatism. Results The astigmatic change decreased over time in Group B (P<0.05). The other groups tended to remain in induced astigmatism. All groups showed anticlockwise torque at 3 weeks following surgery. Group B showed a decrease in deviation, but the other groups showed increases in their torque value at postoperative 12 months (P<0.05). Conclusions The 3.0 mm incision size correlated with the least surgically induced astigmatism. PMID:17460424

  18. Transverse-mode astigmatism in a diode-pumped unstable resonator Nd:YVO{sub 4} laser

    SciTech Connect

    Cheng, Y.; Fanning, C.G.; Siegman, A.E.

    1997-02-01

    We have observed a sizable astigmatism in the output beam from a diode-pumped unstable resonator Nd:YVO{sub 4} laser operating in a single polarization and a single-longitudinal and transverse mode. The anisotropic index of refraction of the vanadate crystal has been identified as the source of this astigmatism. A theoretical prediction of the eigenmode astigmatism based on this index anisotropy is consistent with our experimental measurements. {copyright} 1997 Optical Society of America

  19. Prevalence of Corneal Astigmatism in Tohono O'odham Native American Children 6 Months to 8 Years of Age

    PubMed Central

    Dobson, Velma; Miller, Joseph M.; Schwiegerling, Jim; Clifford-Donaldson, Candice E.; Green, Tina K.; Messer, Dawn H.

    2011-01-01

    Purpose. To describe the prevalence of corneal astigmatism in infants and young children who are members of a Native American tribe with a high prevalence of refractive astigmatism. Methods. The prevalence of corneal astigmatism was assessed by obtaining infant keratometer (IK4) measurements from 1235 Tohono O'odham children, aged 6 months to 8 years. Results. The prevalence of corneal astigmatism >2.00 D was lower in the 1- to <2-year-old age group when compared with all other age groups, except the 6- to <7-year-old group. The magnitude of mean corneal astigmatism was significantly lower in the 1- to <2-year age group than in the 5- to <6-, 6- to <7-, and 7- to <8-year age groups. Corneal astigmatism was with-the-rule (WTR) in 91.4% of astigmatic children (≥1.00 D). Conclusions. The prevalence and mean amount of corneal astigmatism were higher than reported in non–Native American populations. Mean astigmatism increased from 1.43 D in 1-year-olds to nearly 2.00 D by school age. PMID:21460261

  20. Heritability of refractive astigmatism: a population-based twin study among 63- to 75-year-old female twins.

    PubMed

    Pärssinen, Olavi; Kauppinen, Markku; Kaprio, Jaakko; Koskenvuo, Markku; Rantanen, Taina

    2013-09-09

    To examine the heritability of refractive astigmatism in older women. Astigmatism was measured with an autorefractor in 88 monozygotic and 82 dizygotic female twin pairs aged 63 to 75 years. The prevalence and distribution of astigmatism and polar values J0 and J45 were estimated by standard statistical methods. Bivariate maximum likelihood model fitting was used to estimate genetic and environmental variance components using information from both eyes. Mean astigmatism of the more astigmatic eye was 0.93 diopters (D; SD ±0.58). Astigmatism of at least 0.25 D, 0.5 D, 0.75 D, or 1.0 D in either eye was present in 99.7%, 88.5%, 66.5%, and 46.2% of cases, respectively. The main direction of astigmatism was against the rule. The age-adjusted quantitative genetic modeling revealed that additive genetic effects accounted for 33.3% (95% confidence interval [CI], 21.9%-43.8%) of the total variance of astigmatism and for 18% (95% CI, 4%-31%) of the total variance of polar value J45 of both eyes (bivariate model), with the remaining variances due to nongenetic effects. There were no significant correlations between the twin pairs for polar value J0. In elderly female twins, additive genetic effects accounted for one-third of the variance of the amount of astigmatism and only a small fraction of the total variance of polar value J45.

  1. The Effect of Corneal Irregularity on Astigmatism Measurement by Automated versus Ray Tracing Keratometry

    PubMed Central

    Roh, Hyun Cheol; Chuck, Roy S.; Lee, Jimmy K.; Park, Choul Yong

    2015-01-01

    Abstract The aim of this study was to compare the effect of corneal irregularity on astigmatism assessment using automated keratometry (AK) (IOLMaster) versus ray tracing keratometry (Pentacam). This is an observational case series approved by the institutional review board of Dongguk University Hospital, Goyang, South Korea. A total of 207 eyes of 207 cataract patients were included. Preoperative corneal astigmatism was measured by both IOLMaster and Pentacam. Corneal irregularity index (IR) was calculated in Fourier analysis map of Pentacam. AK by IOLMaster and total corneal refractive power (TCRP, 3 mm and 4 mm zone analysis with pupil centered) by Pentacam were selected and the difference between the 2 measurements (delta Δ) was calculated using vector analysis. Ocular residual astigmatism (ORA) after cataract surgery was calculated by subtracting 6-month postoperative refractive astigmatism (RA) measurements from corresponding preoperative values (AK, TCRP3, and TCRP4). The mean irregularity index measured was 0.042 ± 0.019 mm (mean ± standard deviation) and was positively correlated with age and magnitude of corneal astigmatism (P < 0.001 and P < 0.05). The difference (Δ) between TCRPs and AK (ΔTCRPs-AK) was 0.43 ± 0.37 (TCRP3) and 0.39 ± 0.35 (TCRP4) diopters. Linear regression analysis revealed that age (P < 0.001), IR (P < 0.001), and AK (P < 0.001) were positively correlated with ΔTCRPs-AK. In highly irregular corneas (IR over 0.77 diopters: mean + 2 standard deviation), postoperative ORAs calculated using TCRPs were significantly lower than ORAs calculated using AK. Corneal irregularities significantly impact astigmatism assessment by IOLMaster (AK) and Pentacam (TCRPs). Compared with AK, TCRPs were more accurate in predicting postoperative residual astigmatism in highly irregular corneas. PMID:25837759

  2. Astigmatism Correction With Toric Intraocular Lenses in Descemet Membrane Endothelial Keratoplasty Triple Procedures.

    PubMed

    Yokogawa, Hideaki; Sanchez, P James; Mayko, Zachary M; Straiko, Michael D; Terry, Mark A

    2017-03-01

    To report the clinical efficacy of astigmatism correction with toric intraocular lenses (IOLs) in patients undergoing the Descemet membrane endothelial keratoplasty (DMEK) triple procedure and to evaluate the accuracy of the correction. Fifteen eyes of 10 patients who received cataract extraction, toric IOL placement, and DMEK surgery for Fuchs corneal dystrophy and cataracts were evaluated. The cylinder power of toric IOLs was determined by an online toric calculator with keratoscopy measurements obtained using Scheimpflug corneal imaging. Prediction errors were assessed as a difference vector between the anticipated minus postoperative residual astigmatism. At 10.1 ± 4.9 months postoperatively, 8/13 (61.5%) of eyes achieved uncorrected distance visual acuity better than 20/40. Mean best spectacle-corrected distance visual acuity (logMAR) improved from 0.21 ± 0.15 preoperatively to 0.08 ± 0.12 postoperatively (P < 0.01). The magnitude of refractive astigmatism was also significantly decreased from 2.23 ± 1.10 D (range 0.75-4.25 D) preoperatively to 0.87 ± 0.75 D (range 0.00-3.00 D) postoperatively (P < 0.01). In 1 eye with rotational misalignment by 43 degrees, we found no improvement of astigmatism. The prediction error of astigmatism at the corneal plane was 0.77 ± 0.54 D (range 0.10-1.77 D). Four eyes with preoperative "with-the-rule" corneal astigmatism had postoperative "against-the-rule" refractive astigmatism. For patients with Fuchs corneal dystrophy and cataracts, use of toric IOLs might be a valuable option in triple DMEK surgery. Additionally, care should be taken to prevent excessive IOL rotation.

  3. Corneal Astigmatism in Patients After Cataract Surgery: A 10-Year Follow-up Study.

    PubMed

    Kim, Hyojin; Whang, Woong-Joo; Joo, Choun-Ki

    2016-06-01

    To report the long-term outcomes of corneal astigmatism after cataract surgery. The study included 55 eyes of 46 patients who underwent cataract surgery with temporal 3-mm clear corneal incisions from January 2001 to December 2003. All patients underwent complete ophthalmological examination including keratometry at the preoperative visit and at 2 months and 10 years after surgery. Only those eyes that underwent a follow-up of 10 years or longer from the time of cataract surgery were enrolled. Arithmetic and vector analyses were performed to obtain the change in corneal astigmatism with advancing age. The mean age of the patients was 59.11 ± 12.33 years (range: 18 to 75 years), and 58.7% of the patients were women. The mean follow-up period was 131.28 ± 14.36 months. The average magnitudes of surgically induced astigmatism and long-term astigmatism change were 0.66 ± 0.42 and 0.57 ± 0.47 diopters (D), respectively. The vector difference was 0.56 ± 0.55 D at 90° ± 0° between the preoperative and 2-month visits. However, there was no difference in vector values between postoperative 2 months and 10 years (0.00 ± 0.74 D at 0° ± 0°). Patients with corneal astigmatism who underwent cataract surgery did not show a long-term against-the-rule change in corneal astigmatism during a 10-year follow-up. These results provide useful information when planning toric intraocular lens implantation in patients with corneal astigmatism. [J Refract Surg. 2016;32(6):404-409.]. Copyright 2016, SLACK Incorporated.

  4. The effect of corneal irregularity on astigmatism measurement by automated versus ray tracing keratometry.

    PubMed

    Roh, Hyun Cheol; Chuck, Roy S; Lee, Jimmy K; Park, Choul Yong

    2015-04-01

    The aim of this study was to compare the effect of corneal irregularity on astigmatism assessment using automated keratometry (AK) (IOLMaster) versus ray tracing keratometry (Pentacam). This is an observational case series approved by the institutional review board of Dongguk University Hospital, Goyang, South Korea. A total of 207 eyes of 207 cataract patients were included. Preoperative corneal astigmatism was measured by both IOLMaster and Pentacam. Corneal irregularity index (IR) was calculated in Fourier analysis map of Pentacam. AK by IOLMaster and total corneal refractive power (TCRP, 3 mm and 4 mm zone analysis with pupil centered) by Pentacam were selected and the difference between the 2 measurements (delta Δ) was calculated using vector analysis. Ocular residual astigmatism (ORA) after cataract surgery was calculated by subtracting 6-month postoperative refractive astigmatism (RA) measurements from corresponding preoperative values (AK, TCRP3, and TCRP4). The mean irregularity index measured was 0.042 ± 0.019 mm (mean ± standard deviation) and was positively correlated with age and magnitude of corneal astigmatism (P < 0.001 and P < 0.05). The difference (Δ) between TCRPs and AK (ΔTCRPs-AK) was 0.43 ± 0.37 (TCRP3) and 0.39 ± 0.35 (TCRP4) diopters. Linear regression analysis revealed that age (P < 0.001), IR (P < 0.001), and AK (P < 0.001) were positively correlated with ΔTCRPs-AK. In highly irregular corneas (IR over 0.77 diopters: mean + 2 standard deviation), postoperative ORAs calculated using TCRPs were significantly lower than ORAs calculated using AK. Corneal irregularities significantly impact astigmatism assessment by IOLMaster (AK) and Pentacam (TCRPs). Compared with AK, TCRPs were more accurate in predicting postoperative residual astigmatism in highly irregular corneas.

  5. Corneal Astigmatism Stability in Descemet Membrane Endothelial Keratoplasty for Fuchs Corneal Dystrophy.

    PubMed

    Yokogawa, Hideaki; Sanchez, P James; Mayko, Zachary M; Straiko, Michael D; Terry, Mark A

    2016-07-01

    To calculate the magnitude and angle of the shift in corneal astigmatism associated with Descemet membrane endothelial keratoplasty (DMEK) surgery to determine the feasibility of concurrent astigmatism correction at the time of DMEK triple procedures. Retrospective study. Forty-seven eyes that previously underwent the DMEK procedure for Fuchs endothelial corneal dystrophy and that had more than 1.0 diopter (D) of front corneal astigmatism preoperatively were identified. All DMEK surgeries used a clear corneal temporal incision of 3.2 mm. Surgically induced astigmatism (SIA) was evaluated 6 months postsurgery with vector analysis using Scheimpflug image reading. We did not find a difference between pre- and postoperative magnitude of front astigmatism (P = 0.88; paired t test). The magnitude of the SIA front surface was 0.77 ± 0.63 D (range, 0.10-3.14 D). The centroid vector of the SIA front surface was 0.14 at 89.3°. A hyperopic corneal power shift was noted in both the front surface by 0.26 ± 0.74 D (range, 0.45-3.05 D) (P = 0.018; paired t test) and back surface by 0.56 ± 0.55 D (range, 0.25-2.40 D) (P < 0.01; paired t test). DMEK surgery induces minimal amounts of corneal astigmatism that is a with-the-rule shift associated with a temporal clear corneal incision. The stability of these data from preop to postop supports the plausibility of incorporating astigmatism correction with the cautious use of toric intraocular lenses for patients with Fuchs corneal dystrophy and cataract.

  6. Femtosecond Laser-assisted Arcuate Keratotomy Versus Toric IOL Implantation for Correcting Astigmatism.

    PubMed

    Yoo, Aeri; Yun, Samyoung; Kim, Jae Yong; Kim, Myoung Joon; Tchah, Hungwon

    2015-09-01

    To evaluate the clinical efficacy and safety of femtosecond laser-assisted arcuate keratotomy (FS-AK) versus toric intraocular lens (IOL) implantation for correcting astigmatism in patients with cataract. A retrospective chart review was performed. All patients had senile cataracts with corneal astigmatism (range: +1.00 to +3.00 diopters [D]) before cataract surgery. Twenty-five patients agreed to undergo toric IOL implantation (the toric IOL group). Twenty-three patients did not agree to undergo toric IOL implantation despite astigmatism; however, these patients were not satisfied with their remaining astigmatism following cataract surgery and requested astigmatism correction using FS-AK (the FS-AK group). Visual acuity and intraocular pressure were evaluated, and automated refraction, keratometry, and slit-lamp examinations were performed at 1 day, 1 week, 1 month, and 5 months after surgery. Refractive astigmatism decreased in both groups. The mean preoperative and postoperative refractive cylinders were 1.71 ± 1.15 and 0.78 ± 1.06 D, respectively, in the FS-AK group (P < .001) and 1.67 ± 0.13 and 0.83 ± 0.097 D, respectively, in the toric IOL group (P < .001). There were no statistically significant differences between groups at any time during the follow-up period. FS-AK is a fast, customizable, adjustable, precise, and safe procedure for reducing refractive errors in patients with residual astigmatism after cataract surgery. The results of this procedure are comparable to the toric IOL. Copyright 2015, SLACK Incorporated.

  7. Bi-directional corneal accommodation in alert chicks with experimentally-induced astigmatism.

    PubMed

    Chu, Chin-Hung Geoffrey; Zhou, Yongjin; Zheng, Yongping; Kee, Chea-Su

    2014-05-01

    This study aimed to characterize corneal accommodation in alert chicks with and without experimentally-induced astigmatism. Refraction and corneal biometry were measured in 16 chicks with experimentally-induced astigmatism (>1.00 D) and 6 age-matched control chicks (astigmatism ⩽ 1.00 D). Corneal accommodation was detected using a Placido-ring based videokeratography system, by measuring changes in corneal curvature from a series of consecutive images acquired from alert chicks. The correlation between the magnitudes of corneal accommodation and astigmatism was analyzed by including data from all 22 chicks. Data from all eyes showed obvious bi-directional changes in corneal accommodation. There was no significant difference in corneal accommodative changes between the fellow eyes of the treated birds, and the right and left eyes of control birds. However, positive accommodation (PA) and maximum magnitude of PA (MPA) were significantly higher in the astigmatic vs. the fellow eyes of treated chicks (mean ± SE: PA=+2.24 ± 0.44 D vs. +1.26 ± 0.20 D; MPA=+7.53 ± 0.81 D vs. +4.38 ± 0.53 D, both p<0.05). This was not the case for negative accommodation (NA) or maximum magnitude of NA (MNA) (NA=-0.46 ± 0.15 D vs. -0.33 ± 0.04 D; MNA=-0.92 ± 0.23 D vs. -0.73 ± 0.12D, respectively, p>0.05). Furthermore, higher PA and MPA were found to be correlated with higher refractive astigmatism (both r=0.34, p<0.05). These results suggest that the presence of astigmatism may interfere with accommodative function in chicks. Copyright © 2014 Elsevier Ltd. All rights reserved.

  8. A novel color-LED corneal topographer to assess astigmatism in pseudophakic eyes

    PubMed Central

    Ferreira, Tiago B; Ribeiro, Filomena J

    2016-01-01

    Purpose To assess the accuracy of corneal astigmatism evaluation measured by four techniques, Orbscan IIz®, Lenstar LS900®, Cassini®, and Total Cassini (anterior + posterior surface), in pseudophakic eyes. Patients and methods A total of 30 patients (46 eyes) who had undergone cataract surgery with the implantation of a monofocal intraocular lens (AcrySof IQ) were assessed after surgery. For each eye, subjective assessment of astigmatism and its axis was performed. Minimum, maximum, and mean keratometry and astigmatism and its axis were evaluated using the four measurement techniques. All measurements were compared with the subjective measurements. Agreement between each measurement technique and subjective assessment was evaluated using Bland–Altman plots. Linear regressions were performed and compared. Results Linear regression analysis of astigmatism axis showed very high R2 for all models, with Total Cassini showing the least difference to the unit slope (0.052) and the least difference to a null constant (3.790), although not statistically different from the other models. Regarding astigmatism value, the Cassini and Total Cassini models were similar and statistically better than the Lenstar model. Cassini and Total Cassini showed better J0 compared with Orbscan. Conclusion On linear regression models, Cassini and Total Cassini showed the best performance regarding astigmatism value. Cassini and Total Cassini also showed the least J0 deviation from the Cartesian origin compared with Orbscan, which had the lowest performance. Total corneal measurement with the color LED topographer seems to be a better technique for astigmatism assessment. PMID:27574391

  9. Effects of Optically Imposed Astigmatism on Early Eye Growth in Chicks

    PubMed Central

    Chu, Chin Hung Geoffrey; Kee, Chea Su

    2015-01-01

    Purpose To determine the effects of optically imposed astigmatism on early eye growth in chicks. Methods 5-day-old (P5) White Leghorn chicks were randomly assigned to either wear, monocularly, a “high magnitude” (H: +4.00DS/-8.00DC) crossed-cylindrical lens oriented at one of four axes (45, 90, 135, and 180; n = 20 in each group), or were left untreated (controls; n = 8). Two additional groups wore a “low magnitude” (L: +2.00DS/−4.00DC) cylindrical lens orientated at either axis 90 or 180 (n = 20 and n = 18, respectively). Refractions were measured at P5 and after 7 days of treatment for all chicks (P12), whereas videokeratography and ex-vivo eyeshape analysis were performed at P12 for a subset of chicks in each group (n = 8). Results Compared to controls, chicks in the treatment groups developed significant amounts of refractive astigmatism (controls: 0.03±0.22DC; treatment groups: 1.34±0.22DC to 5.51±0.26DC, one-way ANOVAs, p≤0.05) with axes compensatory to those imposed by the cylindrical lenses. H cylindrical lenses induced more refractive astigmatism than L lenses (H90 vs. L90: 5.51±0.26D vs. 4.10±0.16D; H180 vs. L180: 2.84±0.44D vs. 1.34±0.22D, unpaired two-sample t-tests, both p≤0.01); and imposing with-the-rule (H90 and L90) and against-the-rule astigmatisms (H180 and L180) resulted in, respectively, steeper and flatter corneal shape. Both corneal and internal astigmatisms were moderately to strongly correlated with refractive astigmatisms (Pearson’s r: +0.61 to +0.94, all p≤0.001). In addition, the characteristics of astigmatism were significantly correlated with multiple eyeshape parameters at the posterior segments (Pearson’s r: -0.27 to +0.45, all p≤0.05). Conclusions Chicks showed compensatory ocular changes in response to the astigmatic magnitudes imposed in this study. The correlations of changes in refractive, corneal, and posterior eyeshape indicate the involvement of anterior and posterior ocular segments during the

  10. Effects of optically imposed astigmatism on early eye growth in chicks.

    PubMed

    Chu, Chin Hung Geoffrey; Kee, Chea Su

    2015-01-01

    To determine the effects of optically imposed astigmatism on early eye growth in chicks. 5-day-old (P5) White Leghorn chicks were randomly assigned to either wear, monocularly, a "high magnitude" (H: +4.00DS/-8.00DC) crossed-cylindrical lens oriented at one of four axes (45, 90, 135, and 180; n = 20 in each group), or were left untreated (controls; n = 8). Two additional groups wore a "low magnitude" (L: +2.00DS/-4.00DC) cylindrical lens orientated at either axis 90 or 180 (n = 20 and n = 18, respectively). Refractions were measured at P5 and after 7 days of treatment for all chicks (P12), whereas videokeratography and ex-vivo eyeshape analysis were performed at P12 for a subset of chicks in each group (n = 8). Compared to controls, chicks in the treatment groups developed significant amounts of refractive astigmatism (controls: 0.03 ± 0.22DC; treatment groups: 1.34 ± 0.22DC to 5.51 ± 0.26DC, one-way ANOVAs, p ≤ 0.05) with axes compensatory to those imposed by the cylindrical lenses. H cylindrical lenses induced more refractive astigmatism than L lenses (H90 vs. L90: 5.51 ± 0.26D vs. 4.10 ± 0.16D; H180 vs. L180: 2.84 ± 0.44D vs. 1.34 ± 0.22D, unpaired two-sample t-tests, both p ≤ 0.01); and imposing with-the-rule (H90 and L90) and against-the-rule astigmatisms (H180 and L180) resulted in, respectively, steeper and flatter corneal shape. Both corneal and internal astigmatisms were moderately to strongly correlated with refractive astigmatisms (Pearson's r: +0.61 to +0.94, all p ≤ 0.001). In addition, the characteristics of astigmatism were significantly correlated with multiple eyeshape parameters at the posterior segments (Pearson's r: -0.27 to +0.45, all p ≤ 0.05). Chicks showed compensatory ocular changes in response to the astigmatic magnitudes imposed in this study. The correlations of changes in refractive, corneal, and posterior eyeshape indicate the involvement of anterior and posterior ocular segments during the development of astigmatism.

  11. Applicability of supervised discriminant analysis models to analyze astigmatism clinical trial data

    PubMed Central

    Sedghipour, Mohammad Reza; Sadeghi-Bazargani, Homayoun

    2012-01-01

    Background In astigmatism clinical trials where more complex measurements are common, especially in nonrandomized small sized clinical trials, there is a demand for the development and application of newer statistical methods. Methods The source data belonged to a project on astigmatism treatment. Data were used regarding a total of 296 eyes undergoing different astigmatism treatment modalities: wavefront-guided photorefractive keratectomy, cross-cylinder photorefractive keratectomy, and monotoric (single) photorefractive keratectomy. Astigmatism analysis was primarily done using the Alpins method. Prior to fitting partial least squares regression discriminant analysis, a preliminary principal component analysis was done for data overview. Through fitting the partial least squares regression discriminant analysis statistical method, various model validity and predictability measures were assessed. Results The model found the patients treated by the wavefront method to be different from the two other treatments both in baseline and outcome measures. Also, the model found that patients treated with the cross-cylinder method versus the single method didn’t appear to be different from each other. This analysis provided an opportunity to compare the three methods while including a substantial number of baseline and outcome variables. Conclusion Partial least squares regression discriminant analysis had applicability for the statistical analysis of astigmatism clinical trials and it may be used as an adjunct or alternative analysis method in small sized clinical trials. PMID:23055670

  12. Convergence Insufficiency, Accommodative Insufficiency, Visual Symptoms, and Astigmatism in Tohono O'odham Students

    PubMed Central

    Twelker, J. Daniel; Miller, Joseph M.; Campus, Irene

    2016-01-01

    Purpose. To determine rate of convergence insufficiency (CI) and accommodative insufficiency (AI) and assess the relation between CI, AI, visual symptoms, and astigmatism in school-age children. Methods. 3rd–8th-grade students completed the Convergence Insufficiency Symptom Survey (CISS) and binocular vision testing with correction if prescribed. Students were categorized by astigmatism magnitude (no/low: <1.00 D, moderate: 1.00 D to <3.00 D, and high: ≥3.00 D), presence/absence of clinical signs of CI and AI, and presence of symptoms. Analyses determine rate of clinical CI and AI and symptomatic CI and AI and assessed the relation between CI, AI, visual symptoms, and astigmatism. Results. In the sample of 484 students (11.67 ± 1.81 years of age), rate of symptomatic CI was 6.2% and symptomatic AI 18.2%. AI was more common in students with CI than without CI. Students with AI only (p = 0.02) and with CI and AI (p = 0.001) had higher symptom scores than students with neither CI nor AI. Moderate and high astigmats were not at increased risk for CI or AI. Conclusions. With-the-rule astigmats are not at increased risk for CI or AI. High comorbidity rates of CI and AI and higher symptoms scores with AI suggest that research is needed to determine symptomatology specific to CI. PMID:27525112

  13. Assessment of refractive astigmatism and simulated therapeutic refractive surgery strategies in coma-like-aberrations-dominant corneal optics.

    PubMed

    Zhou, Wen; Stojanovic, Aleksandar; Utheim, Tor Paaske

    2016-01-01

    The aim of the study is to raise the awareness of the influence of coma-like higher-order aberrations (HOAs) on power and orientation of refractive astigmatism (RA) and to explore how to account for that influence in the planning of topography-guided refractive surgery in eyes with coma-like-aberrations-dominant corneal optics. Eleven eyes with coma-like-aberrations-dominant corneal optics and with low lenticular astigmatism (LA) were selected for astigmatism analysis and for treatment simulations with topography-guided custom ablation. Vector analysis was used to evaluate the contribution of coma-like corneal HOAs to RA. Two different strategies were used for simulated treatments aiming to regularize irregular corneal optics: With both strategies correction of anterior corneal surface irregularities (corneal HOAs) were intended. Correction of total corneal astigmatism (TCA) and RA was intended as well with strategies 1 and 2, respectively. Axis of discrepant astigmatism (RA minus TCA minus LA) correlated strongly with axis of coma. Vertical coma influenced RA by canceling the effect of the with-the-rule astigmatism and increasing the effect of the against-the-rule astigmatism. After simulated correction of anterior corneal HOAs along with TCA and RA (strategies 1 and 2), only a small amount of anterior corneal astigmatism (ACA) and no TCA remained after strategy 1, while considerable amount of ACA and TCA remained after strategy 2. Coma-like corneal aberrations seem to contribute a considerable astigmatic component to RA in eyes with coma-like-aberrations dominant corneal optics. If topography-guided ablation is programmed to correct the corneal HOAs and RA, the astigmatic component caused by the coma-like corneal HOAs will be treated twice and will result in induced astigmatism. Disregarding RA and treating TCA along with the corneal HOAs is recommended instead.

  14. Comparison of Wavelight Allegretto Eye-Q and Schwind Amaris 750S excimer laser in treatment of high astigmatism.

    PubMed

    Bohac, Maja; Biscevic, Alma; Koncarevic, Mateja; Anticic, Marija; Gabric, Nikica; Patel, Sudi

    2014-10-01

    To compare functional outcomes of Wavelight Allegretto Eye-Q 400Hz and Schwind Amaris 750S excimer laser for astigmatism between 2 and 7 diopters(D). Prospective comparative non-randomized case series of 480 eyes assigned in two laser groups and further divided into myopic and mixed astigmatism subgroups. All treatments were centered on corneal vertex. One-year results were compared between the groups. Statistical analysis was performed using z-test. Both Allegretto and Amaris postoperative uncorrected distance visual acuity (UDVA) improved in comparison to preoperative corrected distance visual acuity (CDVA). The difference was significant in the Allegretto group for myopic astigmatism (p = 0.017). There was no difference in postoperative UDVA between lasers. Average sphere decreased in all groups for both lasers (p < 0.001) without difference in effectiveness of spherical correction between lasers for both groups. In Allegretto, average cylinder decreased from -3.30D to -0.55D in myopic astigmatism (p < 0.001) and from -3.84D to -0.85D in mixed astigmatism (p < 0.001). In Amaris average cylinder decreased from -3.21D to -0.43D in myopic astigmatism (p < 0.001) and from -3.66D to -0.58D in mixed astigmatism (p < 0.001). Amaris group had less residual astigmatism (myopic astigmatism p = 0.023, mixed astigmatism p < 0.001). Mean spherical aberration shifted from positive to negative in mixed astigmatism for both lasers. Both lasers are effective in terms of UDVA, CDVA, spherical correction, and preservation of high-order aberrations. However, Amaris was more effective in cylinder correction.

  15. Distribution and Repeatability of Corneal Astigmatism Measurements (Magnitude and Axis) Evaluated With Color Light Emitting Diode Reflection Topography

    PubMed Central

    Asimellis, George

    2015-01-01

    Purpose: To evaluate and investigate the distribution and repeatability of anterior corneal surface astigmatism measurements (axis and magnitude) using a novel corneal topographer. Methods: Anterior corneal surface astigmatism was investigated in a total of 195 eyes using a novel multicolored spot reflection topographer (Cassini; i-Optics). Two patient groups were studied, a younger-age group A and an older-age group B. Three consecutive acquisitions were obtained from each eye. The repeatability of measurement was assessed using Bland–Altman plot analysis and is reported as the coefficient of repeatability. Results: Group A (average age 34.3 years) had on average with-the-rule astigmatism, whereas the older-age group B (average age 72.3 years) had on average against-the-rule astigmatism. Average astigmatism magnitude measurement repeatability in group A was 0.4 diopters (D) and in group B 0.4 D. Average astigmatism axis measurement repeatability in group A was 5.4 degrees and in group B 5.5 degrees. The axis measurement repeatability improved with increasing magnitude of astigmatism: in the subgroups with astigmatism between 3.0 and 6.0 D, the axis repeatability was 1.4 degrees (group A) and 1.2 degrees (group B), whereas in the subgroups with astigmatism larger than 6.0 D, the repeatability was 1.1 and 0.6 degrees, respectively. Conclusions: This novel corneal topography device seems to offer high precision in reporting corneal astigmatism. This study reaffirms the established trend of a corneal astigmatism shift from an average “with-the-rule” to “against-the-rule” with aging. PMID:26057324

  16. Distribution and Repeatability of Corneal Astigmatism Measurements (Magnitude and Axis) Evaluated With Color Light Emitting Diode Reflection Topography.

    PubMed

    Kanellopoulos, Anastasios John; Asimellis, George

    2015-08-01

    To evaluate and investigate the distribution and repeatability of anterior corneal surface astigmatism measurements (axis and magnitude) using a novel corneal topographer. Anterior corneal surface astigmatism was investigated in a total of 195 eyes using a novel multicolored spot reflection topographer (Cassini; i-Optics). Two patient groups were studied, a younger-age group A and an older-age group B. Three consecutive acquisitions were obtained from each eye. The repeatability of measurement was assessed using Bland-Altman plot analysis and is reported as the coefficient of repeatability. Group A (average age 34.3 years) had on average with-the-rule astigmatism, whereas the older-age group B (average age 72.3 years) had on average against-the-rule astigmatism. Average astigmatism magnitude measurement repeatability in group A was 0.4 diopters (D) and in group B 0.4 D. Average astigmatism axis measurement repeatability in group A was 5.4 degrees and in group B 5.5 degrees. The axis measurement repeatability improved with increasing magnitude of astigmatism: in the subgroups with astigmatism between 3.0 and 6.0 D, the axis repeatability was 1.4 degrees (group A) and 1.2 degrees (group B), whereas in the subgroups with astigmatism larger than 6.0 D, the repeatability was 1.1 and 0.6 degrees, respectively. This novel corneal topography device seems to offer high precision in reporting corneal astigmatism. This study reaffirms the established trend of a corneal astigmatism shift from an average "with-the-rule" to "against-the-rule" with aging.

  17. Sulcus fixated injectable toric intraocular lens to correct astigmatism following penetrating keratoplasty in a pseudophakic eye

    PubMed Central

    Srinivasan, Sathish; Lyall, Douglas; Watt, John

    2010-01-01

    A 56-year-old Caucasian male was referred to the corneal service for the management of post penetrating keratoplasty (PK) astigmatism in his right eye. He had also previously undergone trabeculectomy and cataract surgery in the same eye. Corneal topography showed high postoperative astigmatism of 8.74 dioptres. He was intolerant to contact lens wear and could not tolerate spectacle correction due to high anisometropia. He proceeded to undergo a secondary ‘piggyback’ toric intraocular lens (IOL) insertion procedure with an improvement in his best corrected visual acuity to 6/9. With the decrease in anisometropia he was able to tolerate a full spectacle correction. We report the use of a new injectable sulcus fixated toric piggyback IOL for the correction of post PK astigmatism in a pseudophakic eye. To the best of our knowledge this is the first report on the use of this new ‘add on’ IOL for this clinical condition.

  18. Induced corneal astigmatism by palpebral spring for the treatment of lagophthalmos.

    PubMed

    Avni-Zauberman, Noah; Rosen, Nachum; Ben Simon, Guy J

    2008-08-01

    To report a patient with decreased vision after insertion of an upper eyelid palpebral spring. Interventional case report. A 44-year-old man presented with decreased vision in his right eye. Several months before presentation, he underwent palpebral spring insertion in his upper eyelid for lagophthalmos. He had developed seventh cranial nerve palsy after removal of the right facial nerve neuroma. Decreased vision was related to induced astigmatism by upper eyelid pressure. Surgical replacement of the spring resulted in less astigmatism and improvement in visual acuity. Ocular rehabilitation surgery with insertion of a palpebral spring to the upper eyelid may induce corneal astigmatism and decrease vision in the normal eye. This may be reversible by replacing or repositioning the spring so that it will imply less corneal pressure.

  19. Broadband astigmatism-free Czerny-Turner imaging spectrometer using spherical mirrors

    SciTech Connect

    Austin, Dane R.; Witting, Tobias; Walmsley, Ian A.

    2009-07-01

    We describe the elimination of the astigmatism of a Czerny-Turner imaging spectrometer, built using spherical optics and a plane grating, over a broad spectral region. Starting with the principle of divergent illumination of the grating, which removes astigmatism at one chosen wavelength, we obtain design equations for the distance from the grating to the focusing mirror and the detector angle that remove the astigmatism to first order in wavelength. Experimentally, we demonstrate near diffraction-limited performance from 740 to 860 nm and over a 5 mm transverse spatial extent, while ray-tracing calculations show that barring finite-aperture and detector size limitations, this range extends from 640 to 900 nm and over 10 mm transversely. Our technique requires no additional optics and uses standard off-the-shelf components.

  20. Astigmatism and Myopia in Tohono O'odham Native American Children

    PubMed Central

    Twelker, J. Daniel; Miller, Joseph M.; Sherrill, Duane L.; Harvey, Erin M.

    2014-01-01

    Purpose To describe change in spherical equivalent (M) in a longitudinal sample of Tohono O'odham students ages 3 to 18 years and to test the hypothesis that astigmatism creates complex cues to emmetropization, resulting in increased change in M in the direction of increasing myopia and increased occurrence of myopia. Methods Subjects were 777 Tohono O'odham Native American children on whom cycloplegic right eye autorefraction was measured on at least two study encounters between ages 3 and 18 years (first encounter prior to age 5.5 years, final encounter ≥ 3 years later). Regression lines were fit to individual subjects’ longitudinal M data to estimate rate of change in M (regression slope, D/year). Regression was also used to predict if a subject would be myopic (≤−0.75D M) by age 18 years. ANCOVA was used to assess the relation between M slope and magnitude of baseline M and astigmatism. Chi-square analyses were used to assess the relation between predicted myopia onset and magnitude of baseline M and astigmatism. Results Mean M slope was significantly more negative for hyperopes (M ≥ +2.00) than for myopes (M ≤ −0.75) or for subjects neither hyperopic nor myopic (NHM, M > −0.75 and < +2.00), but there was no significant difference between the myopic and NHM groups. Chi-square analysis indicated that final myopia status varied across level of baseline astigmatism. Subjects with high astigmatism were more likely to be predicted to have significant myopia by age 18 years. Conclusions The association between greater shift in M towards myopia with age in subjects who were hyperopic at baseline is consistent with continued emmetropization in the school years. Results regarding predicted myopia development imply that degradation of image quality due to refractive astigmatism creates complex cues to emmetropization, resulting in increased occurrence of myopia. PMID:24100480

  1. Evaluation of biometry and corneal astigmatism in cataract surgery patients from Central China.

    PubMed

    Yu, Ji-Guo; Zhong, Jie; Mei, Zhong-Ming; Zhao, Fang; Tao, Na; Xiang, Yi

    2017-04-26

    To evaluate the distribution of biometric parameters and corneal astigmatism using the IOLMaster device before phacoemulsification in cataract patients in Central China. Consecutive cataract patients were recruited at the Central Hospital of Wuhan between January 2015 and June 2016. Ocular axial length (AL), keratometry values, anterior chamber depth (ACD) and horizontal corneal diameter (white to white [WTW]) of each cataract-affected eye were measured with the IOLMaster device. The study evaluated 3209 eyes of 2821 cataract patients. The mean AL, ACD, and WTW were 24.38 ± 2.47 mm, 3.15 ± 0.48 mm, and 11.63 ± 0.43 mm, respectively. Corneal astigmatism of 0.51-1.00 diopters (D) was the most common range of values (34.96%). A total of 10.56% patients exhibited a corneal astigmatism greater than 2.0 D. The flat and steep keratometry values gradually increased with age. The mean ACD and WTW showed increasing trends as the AL increased (P < 0.001). When the AL was shorter than 26.0 mm, the keratometry decreased as AL increased. The against-the-rule (ATR) astigmatism proportion increased with age and the with-the-rule (WTR) astigmatism proportion decreased with age. The profile of ocular biometric data and corneal astigmatism may help ophthalmologists improve their surgical procedures and make an appropriate IOL choice to gain a high quality of postoperative vision.

  2. Sequential selective same-day suture removal in the management of post-keratoplasty astigmatism

    PubMed Central

    Fares, U; Mokashi, A A; Elalfy, M S; Dua, H S

    2013-01-01

    Aims In a previous study, we proposed that corneal topography performed 30–40 min after the initial suture removal can identify the next set of sutures requiring removal, for the treatment of post-keratoplasty astigmatism. The aim of this study was to evaluate the effect of removing subsequent sets of sutures at the same sitting. Methods 10/0 nylon interrupted sutures were placed, to secure the graft–host junction, at the time of keratoplasty. Topography was performed using Pentacam (Oculus) before suture removal. The sutures to be removed in the steep semi-meridians were identified and removed at the slit-lamp biomicroscope. Topography was repeated 30–40 min post suture removal, the new steep semi-meridians determined, and the next set of sutures to be removed were identified and removed accordingly. Topography was repeated 4–6 weeks later and the magnitude of topographic astigmatism was recorded. A paired-samples t-test was used to evaluate the impact of selective suture removal on reducing the magnitude of topographic and refractive astigmatism. Results Twenty eyes of 20 patients underwent sequential selective same-day suture removal (SSSS) after corneal transplantation. This study showed that the topographic astigmatism decreased by about 46.7% (3.68 D) and the refractive astigmatism decreased by about 37.7% (2.61 D) following SSSS. Vector calculations also show a significant reduction of both topographic and refractive astigmatism (P<0.001). Conclusion SSSS may help patients to achieve satisfactory vision more quickly and reduce the number of follow-up visits required post keratoplasty. PMID:23743526

  3. Symmetry of the spatial structure of radiation upon transverse mode locking in an astigmatic resonator laser

    SciTech Connect

    Bezotosnyi, V V; Gorbunkov, Mikhail V; Cheshev, E A; Kostryukov, P V; Tunkin, V G; Yakovlev, D V

    2009-08-31

    The influence of the astigmatic resonator parameters on the symmetry of the spatial structure of the radiation intensity is analysed upon transverse mode locking in a nonuniformly pumped laser. Conditions for the transition from the circular symmetry to its violation are found. At a fixed astigmatism of the resonator, the symmetry is determined, first of all, by the resonator length and losses. The theoretical conclusions are confirmed by the experiments with diode end-pumped Nd:YAG and Nd:YLF lasers. (resonators)

  4. Distribution of astigmatism as a function of age in an Australian population.

    PubMed

    Sanfilippo, Paul G; Yazar, Seyhan; Kearns, Lisa; Sherwin, Justin C; Hewitt, Alex W; Mackey, David A

    2015-08-01

    Astigmatism is a common cause of refractive error and is known to vary in prevalence with age. Although the search for genes associated with spherical refractive errors (especially myopia) has met with limited success, current efforts to identify genetic variants implicated in astigmatism development have been less rewarding. We aimed to assess the association between astigmatism and age to identify appropriate age cut-offs for maximizing power in genetic studies of astigmatism. We performed a cross-sectional analysis of right eye astigmatism data from four Australian-based eye studies comprising 3841 participants aged 5-90 years. Measurements were performed under cycloplegia using an autorefractor, and individuals with a history of cataract, refractive surgery or corneal pathology were excluded from the analysis. In addition to the magnitude and type (against-the-rule, with-the-rule, and oblique) of astigmatism, we calculated the vector components (J0 , J45 ) and evaluated the association of these outcome measures with age. The magnitude of refractive astigmatism (RA) remained relatively stable [mean ± SD (-0.44 D ± 0.50)] until individuals reached the age of 50, thereafter increasing in average magnitude by approximately 1.00 D for those subjects aged 90. In contrast, corneal astigmatism (CA) remained relatively stable from childhood until the age of 80 (-0.76 D ± 0.61). The prevalence of clinically significant RA (≥1.00 D) increased with age and was highest in those aged >70 years [55.1% (47.2-62.7%)]. Age was significantly associated with RA in adults [odds ratio (OR) = 1.04 per 1 year, p < 0.001]. A weaker relationship was observed between CA and age (OR = 1.007 per 1 year, p = 0.02). We have confirmed the previously documented association between RA and age. Our results indicate that most of the observed change occurs after the age of 50, providing a recommended cut-off for participants in genetic studies of this refractive condition. © 2015 Acta

  5. Astigmatism correction in x-ray scanning photoemission microscope with use of elliptical zone plate

    SciTech Connect

    Ade, H.; Ko, C. ); Anderson, E. )

    1992-03-02

    We report the impact of an elliptical, high resolution zone plate on the performance of an initially astigmatic soft x-ray scanning photoemission microscope. A zone plate with carefully calibrated eccentricity has been used to eliminate astigmatism arising from transport optics, and an improvement of about a factor of 3 in spatial resolution was achieved. The resolution is still dominated by the source size and chromatic aberrations rather than by diffraction and coma, and a further gain of about a factor of 2 in resolution is possible. Sub 100 nm photoemission microscopy with primary photoelectrons is now within reach.

  6. Astigmatism and biometric optic components of diode laser-treated threshold retinopathy of prematurity at 9 years of age

    PubMed Central

    Yang, C-S; Wang, A-G; Shih, Y-F; Hsu, W-M

    2013-01-01

    Purpose To assess the prevalence of astigmatism and its relationship with biometric optic components in preterm school children with diode laser-treated threshold retinopathy of prematurity (ROP). Methods A prospective, cross-sectional study in which cycloplegic keratometry, refraction, and ultrasound biometric measurement of optic components were performed on 24 consecutive preterm children with diode laser-treated threshold ROP at the age of 9 years. The study results were compared with data on 1021 age-matched full-term control children from a national survey. Results The laser-treated eyes had a mean astigmatism of 3.47 D, with a mean spherical equivalent of −4.49 D. Of the 46 eyes studied, 98% of eyes showed astigmatism ≥0.5 D and 50% had high astigmatism (>3.0 D). Most astigmatic eyes (97.7%) showed with-the-rule astigmatism, with the mean plus cylinder axis at 89.30o. Further correlation analysis showed the astigmatism in refraction was highly correlated with the corneal astigmatism (r=0.921, P<0.001) and the vertical corneal curvature (r=0.405, P=0.005). There was significantly steeper vertical corneal curvature (P=0.003) and flatter horizontal corneal curvature (P=0.031) in eyes with laser-treated ROP when compared with age-matched full-term controls. The eyes with laser-treated ROP also show significantly thicker lens (3.93 mm) and shallower anterior chamber depth (ACD; 2.92 mm) than full-term controls (P<0.001). Conclusions There is significantly higher prevalence and greater magnitude of astigmatism in eyes with laser-treated threshold ROP compared with full-term controls. The steeper vertical corneal curvature component contributes to the increased astigmatism in eyes with laser-treated ROP. PMID:23222565

  7. Toric intraocular lens orientation and residual refractive astigmatism: an analysis

    PubMed Central

    Potvin, Rick; Kramer, Brent A; Hardten, David R; Berdahl, John P

    2016-01-01

    Purpose To analyze intraocular lens (IOL) orientation data from an online toric back-calculator (astigmatismfix.com) for determining if differences were apparent by lens type. Methods A retrospective review of astigmatismfix.com toric back-calculations that included IOL identification and intended orientation axis. Results Of 12,812 total validated calculation records, 8,229 included intended orientation and lens identification data. Of the latter, 5,674 calculations (69%) involved lenses oriented 5° or more from their intended position. Using estimated toric lens usage data, the percentage of lenses with orientation ≥5° from intended was 0.89% overall, but the percentage varied significantly between specific toric lens brands (P<0.05). The percentage of back-calculations related to lenses that were not oriented as intended was also statistically significantly different by lens brand (P<0.05). When IOLs were misoriented, they were significantly more likely to be misoriented in a counterclockwise direction (P<0.05). This was found to be due to a bias toward counterclockwise orientation observed with one specific brand, a bias that was not observed with the other three brands analyzed here. Conclusion The percentage of eyes with lens orientation ≥5° from intended in the Toric Results Analyzer data set was <1% of toric IOLs in general, with the relative percentage of Tecnis® Toric IOLs significantly higher than AcrySof® Toric IOLs. Both of these had higher rates than the Staar® Toric and Trulign® Toric lenses, with the availability of higher Tecnis and AcrySof cylinder powers a likely contributing factor. The AcrySof Toric IOL appears to be less likely than the Tecnis Toric IOL to cause residual astigmatism as a result of misorientation. The Tecnis Toric IOL appears more likely to be misoriented in a counterclockwise direction; no such bias was observed with the AcrySof Toric, the Trulign® Toric, or the Staar Toric IOLs. PMID:27703323

  8. Prevalence of Corneal Astigmatism and Anterior Segmental Biometry Characteristics Before Surgery in Chinese Congenital Cataract Patients

    PubMed Central

    Lin, Duoru; Chen, Jingjing; Liu, Zhenzhen; Wu, Xiaohang; Long, Erping; Luo, Lixia; Lin, Zhuoling; Li, Xiaoyan; Zhang, Li; Chen, Hui; Liu, Jinchao; Chen, Weirong; Lin, Haotian; Liu, Yizhi

    2016-01-01

    The prevalence and the distribution characteristics of corneal astigmatism (CA) and anterior segment biometry before surgery in Chinese congenital cataract (CC) patients are not completely understood. This study involved 400 CC patients from the Zhongshan Ophthalmic Center enrolled from February 2011 to August 2015. Data on CA, keratometry, central corneal thickness (CCT) and anterior chamber depth (ACD) were measured by the Pentacam Scheimpflug System. The mean age of patients was 54.27 months, and the ratio of boys to girls was 1.53:1. The mean CA was 2.03 diopters (D), and 39.25% of subjects had CA values ≥2 D. The most frequent (71.8%) diagnosis was with-the-rule astigmatism. Oblique astigmatism was present in 16.2% of cases, and 12% of cases had against-the-rule astigmatism. The mean keratometry measurement of cataractous eyes in bilateral patients was significantly larger than that in unilateral patients. Girls had a larger mean keratometry but a thinner CCT than did boys. The CA, CCT, and ACD of cataractous eyes were significantly larger than those of non-cataractous eyes in unilateral patients. The CA, mean keratometry, CCT, and ACD in CC patients varied with age, gender, and laterality. Fully understanding these characteristics may help inform guidelines and treatment decisions in CC patients. PMID:26912400

  9. Normalisation of asymmetric astigmatism after intralesional steroid injection for upper eye lid hemangioma in childhood.

    PubMed

    Langmann, A; Lindner, S

    1994-01-01

    Infantile hemangiomas affect about 5% (3%-8%) of the population, showing a predilection for the face. After a phase of rapid enlargement between the 3rd and the 9th month of life, 70% regress by the age of six after a period of stability. 43%-60% of the children with eye lid hemangiomas develop strabismic, anisometropic, or deprivation amblyopia. Previous studies found the majority of cases resulting from anisometropia (especially asymmetric astigmatism) rather than strabism or occlusion of the visual axis. Several methods of treatment--surgical excision, irradiation, sclerosing agents, systemic steroids, ligation, cryotherapy--have been used but all with a risk of local or systemic complications. Local injections of steroids are a simple method of therapy with a high rate of resolution of hemangiomas, but still with a high degree of bad visual output because of persistent astigmatism. In four children with asymmetric astigmatism (axis of astigmatism towards the hemangioma) in which the injection was given at the beginning of the phase of enlargement, amblyopia could be avoided by preventing corneal steepening from becoming permanent.

  10. Vision of low astigmats through thick and thin lathe-cut soft contact lenses.

    PubMed

    Cho, P; Woo, G C

    2001-01-01

    Distance and near visual acuity of 13 low astigmats were determined in a double-masked experiment through thick and thin (centre thickness 0.12 mm and 0.06 mm, respectively) spherical lathe-cut soft lenses. For each lens type, distance and near LogMAR VA and over-refraction were assessed with different logMAR VA charts. For 70% of the subjects, the residual astigmatism was significantly lower than the refractive astigmatism with thicker lenses. No statistically significant differences in the distance and near logMAR VA was found between the two lens types using any of the charts used, though, in general, logMAR VA obtained through the thicker lens was better than logMAR VA through the thinner lens. The variabilities in distance and near logMAR VA between the two lens types increased with decreased contrast. The variabilities in distance logMAR VA were greater with Chinese charts than with English charts, and LogMAR VA with Chinese charts were significantly worse for both lens types. Based on the results of this study, we concluded that thicker spherical lathe-cut soft lenses provide better vision in low astigmats. The Snellen acuity test is inadequate for vision assessment of soft contact lens wearers. When a patient wearing thin soft contact lenses complains of poor vision in spite of 6/6 or 6/5 Snellen acuity, changing to thicker lenses may be considered.

  11. Optical-vortex pair creation and annihilation and helical astigmatism of a nonplanar ring resonator

    SciTech Connect

    Heckenberg, N.R.; Vaupel, M.; Malos, J.T.; Weiss, C.O.

    1996-09-01

    The creation and annihilation of pairs of optical vortices have been studied in transitions between patterns produced in a photorefractive oscillator. Smooth metamorphosis between stable patterns occurs through pair creation or annihilation but can be modeled using superposition of modes taking into account lifting of degeneracy of helical modes by helical astigmatism of the resonator. {copyright} {ital 1996 The American Physical Society.}

  12. Height measurement of astigmatic test surfaces by a keratoscope that uses plane geometry surface reconstruction.

    PubMed

    Tripoli, N K; Cohen, K L; Obla, P; Coggins, J M; Holmgren, D E

    1996-06-01

    To assess the accuracy with which the Keratron keratoscope (Optikon 2000, Rome, Italy) measured astigmatic test surfaces by a profile reconstruction algorithm within a plane geometry model and to discriminate between error caused by the model and error caused by other factors. Height was reported by the Keratron for eight surfaces with central astigmatism ranging from 4 to 16 diopters. A three-dimensional ray tracing simulation produced theoretic reflected ring patterns on which the Keratron's reconstruction algorithm was performed. The Keratron's measurements were compared with the surfaces' formulas and the ray-traced simulations. With a new mathematical filter for smoothing ring data, now part of the Keratron's software, maximum error was 0.47% of the total height and was usually less than 1% of local power for surfaces with 4 diopters of astigmatism. For surfaces with 16 diopters of astigmatism, maximum error was as high as 2.9% of total height and was usually less than 2.5% of local power. The reconstruction algorithm accounted for 40% and 70% of height error, respectively. The efficacy of keratoscopes cannot be assumed from their design theories but must be tested. Although plane geometry surface reconstruction contributed greatly to total height error, total error was so small that it is unlikely to affect clinical use.

  13. Refractive and Quality of Vision Outcomes with Toric IOL Implantation in Low Astigmatism

    PubMed Central

    Patrão, Lia Florim; de Moraes, Haroldo Vieira

    2016-01-01

    Purpose. To evaluate the refractive and the quality of vision outcomes of toric IOL implantation in patients with low astigmatism. Design. Prospective study of single-arm. Methods. Patients with corneal astigmatism range from 0,75 D to 1,5 D and cataract that underwent cataract surgery with toric IOL. The measurements were performed preoperatively and 6 weeks after the surgery. Patients were evaluated for visual acuity with and without correction, contrast sensitivity, static and dynamic refraction, and quality of life questionnaire. Pre- and postoperative values were compared and their variations were evaluated for linear correlation. Results. 21 eyes of 21 patients. Postoperative mean uncorrected visual acuity was 0.80 ± 0.19, and the best corrected visual acuity was 0.97 ± 0.15. p < 0.001 compared to preoperative values. The average postoperative refractive cylinder was −0.34 ± 0.39. The questionnaire's total value before and after surgery was, respectively, 43.20 ± 15.76 and 79.70 ± 10.11 (p < 0.001). The correlation coefficients between the values of the questionnaire variation and the UCVA, BCVA, and CS variation were, respectively, 0.548 (p = 0.005), 0.508 (p = 0.009), and 0.409 (p = 0.033). Conclusion. Patients with low astigmatism who underwent phacoemulsification with toric IOL implantation experienced significant decrease in refractive astigmatism and improvement in their quality of life. PMID:28070415

  14. Evaluation of the toric implantable collamer lens for simultaneous treatment of myopia and astigmatism.

    PubMed

    Price, Marianne O; Price, Francis W

    2015-01-01

    Myopic astigmatism is a prevalent condition that can be treated with spectacles, contact lenses, or laser refractive surgery. However, these treatment options have functional limitations at higher levels of refractive error. The toric implantable collamer lens is designed to treat a broad range of refractive error, generally up to -18 diopters with +1 to +6 diopters of astigmatism. Approval for a more limited treatment range of up to 15 diopters of myopia with +1 to +4 diopters of astigmatism is being sought in the US, where this device has not yet received marketing approval. Surgical correction of high-myopic astigmatism can be life-altering and allow people to participate in activities that were not previously feasible because of visual limitations. The toric implantable collamer lens is implanted behind the iris and in front of the natural crystalline lens. With earlier lens designs, it was necessary to create an iridectomy or iridotomy to prevent pupillary block. The newest toric implantable collamer lens model has a small central hole that is not visually noticeable. This eliminates the need to create a hole in the iris, thereby enhancing the safety of the procedure.

  15. Prevalence of Corneal Astigmatism and Anterior Segmental Biometry Characteristics Before Surgery in Chinese Congenital Cataract Patients.

    PubMed

    Lin, Duoru; Chen, Jingjing; Liu, Zhenzhen; Wu, Xiaohang; Long, Erping; Luo, Lixia; Lin, Zhuoling; Li, Xiaoyan; Zhang, Li; Chen, Hui; Liu, Jinchao; Chen, Weirong; Lin, Haotian; Liu, Yizhi

    2016-02-25

    The prevalence and the distribution characteristics of corneal astigmatism (CA) and anterior segment biometry before surgery in Chinese congenital cataract (CC) patients are not completely understood. This study involved 400 CC patients from the Zhongshan Ophthalmic Center enrolled from February 2011 to August 2015. Data on CA, keratometry, central corneal thickness (CCT) and anterior chamber depth (ACD) were measured by the Pentacam Scheimpflug System. The mean age of patients was 54.27 months, and the ratio of boys to girls was 1.53:1. The mean CA was 2.03 diopters (D), and 39.25% of subjects had CA values ≥2 D. The most frequent (71.8%) diagnosis was with-the-rule astigmatism. Oblique astigmatism was present in 16.2% of cases, and 12% of cases had against-the-rule astigmatism. The mean keratometry measurement of cataractous eyes in bilateral patients was significantly larger than that in unilateral patients. Girls had a larger mean keratometry but a thinner CCT than did boys. The CA, CCT, and ACD of cataractous eyes were significantly larger than those of non-cataractous eyes in unilateral patients. The CA, mean keratometry, CCT, and ACD in CC patients varied with age, gender, and laterality. Fully understanding these characteristics may help inform guidelines and treatment decisions in CC patients.

  16. Analysis of astigmatism of gain guided laser with a tapered-stripe geometry

    SciTech Connect

    Mamine, T.; Oda, T.; Yoneyama, O.

    1984-12-01

    The astigmatism of the tapered-stripe (TAPS) laser has been analyzed. Calculating the near-field spot size and the radius of curvature in the tapered-stripe region, the astigmatism is determined by using the expression of D = R/sub e/ (1+(lambdaR/sub e// ..pi..w/sup 2//sub e/)/sup 2/)/sup -1/. In our formalism we assume that the gain profile is parabola and the near-field spot size at the facet is determined by the diffusion length of injected carriers. So far as these assumptions are valid, it is concluded that the amount of astigmatism is reduced with the length of tapered stripe, using the refractive index change due to the band-edge absorption of -10/sup -2/. The fundamental characteristics of the gain guided laser with TAPS structure such as the astigmatism, far-field radiation pattern, and the spontaneous emission factor are shown to be controlled by properly designing the stripe geometry and the thickness of the active layer.

  17. [Post-operative residual astigmatism after cataract surgery: Current surgical methods of treatment].

    PubMed

    Pisella, P-J

    2012-03-01

    Residual astigmatism after cataract surgery can be corrected by three different techniques: classic limbal relaxing incisions, easy to perform but with limited precision; laser refractive surgery (PRK or Lasik), additionally allowing for correction of spherical equivalent; and more recently the use of a piggyback toric intraocular lens in the ciliary sulcus.

  18. The role of sideport incision in astigmatism change after cataract surgery

    PubMed Central

    Theodoulidou, Sofia; Asproudis, Ioannis; Kalogeropoulos, Christos; Athanasiadis, Aristidis; Aspiotis, Miltiadis

    2015-01-01

    Purpose To study the changes in corneal astigmatism after cataract surgery when the sideport incision is performed at a predetermined location away from the tunnel incision. Setting General Hospital of Piraeus “Tzaneio”, Attiki, Greece. Materials and methods A total of 333 eyes with corneal astigmatism ≤1.5 diopters (D) underwent cataract surgery. A three-step superotemporal clear corneal incision for the right eye and a superonasal clear corneal incision for the left eye (3.0 mm) was made, while the sideport incision was located at <90°, 90°–110°, and >110°. Keratometric data were measured with corneal topography EyeSys Vista 2000 pre- and postoperatively at the 1st and 6th month. Surgically induced astigmatism was calculated by vector analysis. We noted all cases in which a change >0.5 D in corneal astigmatic power occurred, as well as a change >20° in axis torque, despite axis direction. Results After multiple logistic regression analysis was conducted, cases with >110° distance between the tunnel and sideport incision had 2.22 times (P=0.021) greater likelihood for having changed >0.5 D in astigmatic power at the 1st month and 3.45 times (P=0.031) at the 6th month postoperatively, as compared with cases with a 90°–110° distance between the tunnel and sideport incision. As for the change in the astigmatic axis, cases with <90° distance had a 4.18 times greater likelihood for having a change >20° (P<0.001) (preoperative to 1st month) as compared with cases having 90°–110° of distance. Conclusion For surgeons that operate only from the superior position, we propose that in order to produce an incision that is as “astigmatically neutral” as possible, they should perform the sideport incision at a 90°–110° distance. PMID:26346741

  19. Pseudophakic astigmatism reduction with femtosecond laser-assisted corneal arcuate incisions: a pilot study

    PubMed Central

    Blehm, Clayton; Potvin, Richard

    2017-01-01

    Purpose The aim of this study was to assess the effectiveness of the Verion-LenSx guided arcuate incision technique to reduce refractive astigmatism in a pseudophakic population. Patients and methods A prospective single-arm study was conducted in which one or both eyes of subjects required reduction of 1.0–2.0 D of refractive astigmatism after previous cataract surgery or refractive lens exchange. The surgeon used the refractive cylinder in the eye and the Woodcock astigmatism nomogram for preoperative planning, while the LenSx femtosecond laser with the Verion Image Guided System was used to create all arcuate incisions. The primary outcome measure was the uncorrected monocular distance visual acuity (UCVA). Secondary outcome measures included the change in corneal astigmatism, the change in refractive astigmatism, the best-corrected visual acuity and spectacle independence at distance from preoperative stage to 1 month and 2 months postoperatively. Results Twenty-eight eyes of 18 subjects were treated. The best-corrected visual acuity at the 2-month postoperative (PO) stage was not statistically significantly different from the preoperative visual acuity (0.02 logarithm of the minimum angle of resolution [logMAR] in both cases, P>0.05). Uncorrected visual acuity was statistically significantly better at the 2-month PO stage relative to the preoperative value (0.14 versus 0.34 logMAR, P<0.01). The mean change in refractive cylinder from the preoperative stage to the 2-month PO stage was 1.0 D. At the 2-month PO stage, two-thirds of the subjects (12/18) reported that they did not use glasses for distance vision and that their spectacle use for distance vision at 2 months was “lower” or “much lower” than the preoperative stage; in 71% of eyes (20/28), the residual refractive cylinder was ≤0.50 D. Vector changes in keratometric astigmatism were weakly associated with changes in refractive cylinder. Conclusion Arcuate incisions made with a femtosecond

  20. Pseudophakic astigmatism reduction with femtosecond laser-assisted corneal arcuate incisions: a pilot study.

    PubMed

    Blehm, Clayton; Potvin, Richard

    2017-01-01

    The aim of this study was to assess the effectiveness of the Verion-LenSx guided arcuate incision technique to reduce refractive astigmatism in a pseudophakic population. A prospective single-arm study was conducted in which one or both eyes of subjects required reduction of 1.0-2.0 D of refractive astigmatism after previous cataract surgery or refractive lens exchange. The surgeon used the refractive cylinder in the eye and the Woodcock astigmatism nomogram for preoperative planning, while the LenSx femtosecond laser with the Verion Image Guided System was used to create all arcuate incisions. The primary outcome measure was the uncorrected monocular distance visual acuity (UCVA). Secondary outcome measures included the change in corneal astigmatism, the change in refractive astigmatism, the best-corrected visual acuity and spectacle independence at distance from preoperative stage to 1 month and 2 months postoperatively. Twenty-eight eyes of 18 subjects were treated. The best-corrected visual acuity at the 2-month postoperative (PO) stage was not statistically significantly different from the preoperative visual acuity (0.02 logarithm of the minimum angle of resolution [logMAR] in both cases, P>0.05). Uncorrected visual acuity was statistically significantly better at the 2-month PO stage relative to the preoperative value (0.14 versus 0.34 logMAR, P<0.01). The mean change in refractive cylinder from the preoperative stage to the 2-month PO stage was 1.0 D. At the 2-month PO stage, two-thirds of the subjects (12/18) reported that they did not use glasses for distance vision and that their spectacle use for distance vision at 2 months was "lower" or "much lower" than the preoperative stage; in 71% of eyes (20/28), the residual refractive cylinder was ≤0.50 D. Vector changes in keratometric astigmatism were weakly associated with changes in refractive cylinder. Arcuate incisions made with a femtosecond laser to treat moderate levels of residual refractive

  1. Nonpenetrating femtosecond laser intrastromal astigmatic keratotomy in eyes having cataract surgery.

    PubMed

    Day, Alexander C; Lau, Nicola M; Stevens, Julian D

    2016-01-01

    To describe the effect of femtosecond laser intrastromal astigmatic keratotomy (AK) performed during cataract surgery. Moorfields Eye Hospital, London, United Kingdom. Prospective case series. This study comprised patients having laser cataract surgery with concurrent astigmatism management by intrastromal AK. All eyes had greater than 0.7 corneal diopter (D) cylinder. An intrastromal AK nomogram with 8.0 mm diameter paired symmetric limbal centered arcs was used. Corneal keratometry was measured preoperatively and 1 month postoperatively using a KR8100PA topographer-autorefractor. Astigmatic analyses were performed using the Alpins method considering 3 vectors-target induced astigmatism (TIA), surgically induced astigmatism (SIA) and difference vector (DV)-and calculation of coupling measures. In all, 196 eyes of 133 patients were analyzed. The mean TIA (equivalent to preoperative corneal cylinder) was 1.21 D ± 0.42 (SD) (range 0.75 to 2.64 D) and the mean SIA was 0.74 DC ± 0.40 (range 0.00 to 2.86). The mean difference vector was 0.74 ± 0.38 D (range 0.00 to 2.25 D). The mean correction index was 0.63 ± 0.32 (range 0.00 to 1.93), indicating that the mean astigmatism correction was 63%. Fourteen eyes (7.1%) and 7 eyes (3.6%) had an astigmatism correction of greater than 100% and greater than 120%, respectively. Overall 0%, 48.5%, and 51.5% of eyes had 0.50 D or less, 1.0 D or less, or greater than 1.0 D, respectively, preoperatively compared with 32.1%, 85.7%, and 14.3%, postoperatively. There were no cases of corneal endothelial perforation or inadvertent placement within the visual axis. The intrastromal AKs were easily programmed as an integral part of laser-assisted cataract surgery without additional cost, significantly reduced corneal cylinder, and appeared to be safe through 1 month of follow-up. Dr. Day was supported by the National Institute for Health Research (NIHR) Biomedical Research Centre based at Moorfields Eye Hospital NHS Foundation Trust and

  2. Microincision Hydrophobic Acrylic Aspheric Toric Intraocular Lens for Astigmatism and Cataract Correction.

    PubMed

    Bissen-Miyajima, Hiroko; Negishi, Kazuno; Hieda, Osamu; Kinoshita, Shigeru

    2015-06-01

    To evaluate the efficacy and safety of a new acrylic one-piece toric intraocular lens (IOL). This prospective multicenter clinical trial included 93 eyes of 61 patients that were implanted with a hydrophobic acrylic toric IOL from 2010 to 2012 and followed for 1 year. This IOL uses the platform of a microincision one-piece aspheric IOL, the NY-60 IOL (HOYA, Tokyo, Japan), with three increments in cylindrical power (NHT15, 1.5 diopters [D]; NHT23, 2.25 D; and NHT30, 3.0 D). The inclusion criterion was preoperative corneal astigmatism from 0.75 to 3.00 D. The primary endpoint was uncorrected distance visual acuity (UDVA) of 0.0 logMAR (20/20 Snellen) or better 6 months postoperatively. In addition to UDVA, corrected distance visual acuity (CDVA), residual astigmatism, stability of the IOL alignment, need of realignment, and the rate of Nd:YAG laser capsulotomy were evaluated up to 1 year postoperatively. Errors in astigmatic correction were assessed using Alpin's vector analysis. The primary endpoint was achieved in 54.8% of eyes. One year postoperatively, the logMAR UDVAs were 0.02 ± 0.13, 0.05 ± 0.17, and 0.09 ± 0.14 with models NHT15, NHT23, and NHT30, which corresponds to 0.96 (19/20 Snellen), 0.89 (18/20 Snellen), and 0.82 (16/20 Snellen), respectively. One year postoperatively, the residual astigmatism was 0.66 ± 0.58 D. In each evaluation, the mean absolute change in the position of the axis mark was between 1.93° and 2.32°. Three eyes required repositioning of the IOL axis and 2 eyes received Nd:YAG laser capsulotomy. The correction error showed an undercorrection with against-the-rule astigmatism and overcorrection with with-the-rule astigmatism. The new one-piece toric IOL provided desirable clinical outcomes and stability in eyes with corneal astigmatism. Copyright 2015, SLACK Incorporated.

  3. [Results of corneal and total astigmatism estimation by different methods in myopic patients wearing orthokeratology contact lenses].

    PubMed

    Tarutta, E P; Aliaeva, O O; Verzhanskaia, T Iu; Milash, S V

    2013-01-01

    Reports have been made that corneal aberrations of all orders, including astigmatism, often significantly increase with the use of night orthokeratology lenses. In this study the dynamic changes of total and corneal astigmatism in myopes using orthokeratology lenses was evaluated by different methods. The study enrolled 38 patients (76 eyes) with low and medium myopia (28 and 48 eyes correspondingly) and initial astigmatism less than 2 diopters. The assessment was made before and in different terms after the patient started to wear orthokeratology lenses. Induced astigmatism (> or =1 diopter) was found in more than 50% of cases. The degree of astigmatism gradually increased from the centre to the periphery within the papillary zone. The maximum values were found within a 4-mm zone ("uptake zone") and minimal - within a 8-mm zone ("equalization zone"). In all patients, despite the presence of induced astigmatism and residual myopia (0.83+/-0.09 diopters in average), distance visual acuity was high enough without an additional correction (0.82+/-0.05 in average). Apparently, in these patients the aberrations (astigmatism in particular) exceed the focal depth.

  4. Axis-free correction of astigmatism using bifocal soft contact lenses.

    PubMed

    Leube, Alexander; Kovats, Imre; Wahl, Siegfried; Sickenberger, Wolfgang

    2017-09-18

    Pilot study to investigate the feasibility of an axis-free correction approach of regular astigmatism using soft, bifocal contact lenses (CL). The investigation covers an optical simulation and a pilot study for the assessment of visual performance (over refraction OR, monocular visual acuity VA). The power of the two zones was adjusted according to the power of the astigmatic meridians, individually. Subjective performance was assessed in 30 participants with a mean horizontal cylindrical component of J0=- 0.65±1.29 D (cylinder from -0.75 to -4.00 DC). OR and VA were measured directly after fitting the CL, after one hour and after 5days (3FUP). Evaluating the modulation transfer function, CL increased the Strehl ratio by 10% and the transferred spatial frequency was improved from 6.6 cpd to 21.3 cpd. Analysis of Sturm's interval revealed a residual astigmatism of DAst=0.73 D. OR revealed a statistically significant reduction of spherical error between baseline and all follow up (ΔM=-2.14 D, p<0.001) and between the J0 from baseline to 3FUP (ΔJ0=-0.46 D, p=0.04). Wearing the CL for 5days did not result in a significant difference of VA (ΔVA3FUP=+0.01 logMAR, p=0.99). Axis-free correction of astigmatism using bifocal CL resulted in reasonable performance based on computer simulation. Participants showed no clinically reduced visual acuity or contrast sensitivity. Further clinical studies are needed to show if this approach provides a good alternative to conventional astigmatic correction. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

  5. Refractive Lenticule Transplantation for Correction of Iatrogenic Hyperopia and High Astigmatism After LASIK.

    PubMed

    Lazaridis, Apostolos; Reinstein, Dan Z; Archer, Timothy J; Schulze, Stephan; Sekundo, Walter

    2016-11-01

    To design a technique for intrastromal transplantation of stromal lenticules with specific refractive power for correction of post-LASIK induced hyperopia and astigmatism. A 28-year-old patient was referred for consultation after complicated LASIK for moderate myopia and astigmatism. The refractive error of the right eye was severely overcorrected due to data entry error. Post-LASIK refraction showed high astigmatism (right eye: +6.50 -9.00 @ 84°) and corrected distance visual acuity (CDVA) of 20/32. The corneal thickness was 282 µm. A refractive lenticule transplantation was performed due to contact lens intolerance, poor visual acuity, and severe anisometropia. A toric and myopic lenticule, obtained from a donor using the femtosecond lenticule extraction technique, was implanted under the flap to reduce the refractive error, bring the refraction of the eye to the level correctable by phakic intraocular lens, and restore corneal volume. Six weeks postoperatively, the donor lenticule was spread smoothly in the interface with a minor temporal decentration in relation to pupil center. The refraction showed a reduction of astigmatism but a stronger myopization compared to preoperative calculations (right eye: -6.50 -4.00 @ 70°). At 3 months, the CDVA returned to the preoperative value of 20/32. One year postoperatively, corneal tomography showed no signs of ectasia and biomicroscopy revealed no signs of rejection. After implanting a toric myopic implantable collamer lens, the patient regained uncorrected distance visual acuity of 20/40 and full stereopsis. The refractive lenticule transplantation technique offers a solution for rare cases of post-LASIK hyperopia and high astigmatism while restoring the volume of thin corneas. Moreover, it is a reversible procedure with low probability of rejection. [J Refract Surg. 2016;32(11):780-786.]. Copyright 2016, SLACK Incorporated.

  6. Changes in Irregular Corneal Astigmatism With Age in Eyes With and Without Cataract Surgery.

    PubMed

    Hayashi, Ken; Kawahara, Sumie; Manabe, Shin-ichi; Hirata, Akira

    2015-12-01

    To investigate the changes in irregular and regular corneal astigmatism with age in eyes that underwent cataract surgery (surgery group) and in eyes that did not undergo surgery (nonsurgery group). We enrolled 120 eyes in each of four age groups in the surgery and nonsurgery groups: (1) 50 to 59 years of age, (2) 60 to 69 years of age, (3) 70 to 79 years of age, and (4) older than or equal to 80 years of age. Eyes in the surgery group underwent videokeratographic examination, at least 6 months postoperatively. Irregular astigmatism components, corneal asymmetry, and higher-order irregularity components were determined using Fourier analysis. The regular astigmatism vector was decomposed into vertical/horizontal (J0) and oblique (J45) components using power vector analysis. Both the mean corneal asymmetry and higher-order irregularity components significantly increased with increasing age in both groups (P < 0.0001). Higher-order irregularity was greater in the surgery group than in the nonsurgery group in all age groups (P ≤ 0.0128). The asymmetry did not differ significantly between groups. Asymmetry and higher-order irregularity were positively correlated with actual age in both the surgery and nonsurgery groups (P < 0.0001). The J0 decreased significantly with age in both groups (P < 0.0001), whereas the J45 did not vary significantly with age. In patients from 50 to 80 years of age who underwent cataract surgery, irregular corneal astigmatism, both the asymmetry and higher-order irregularity components, increased significantly with increasing age, whereas regular astigmatism induces an against-the-rule shift. The higher-order irregularity component persistently increased postoperatively, whereas the asymmetry component did not change significantly.

  7. Small-incision lenticule extraction (SMILE): outcomes of 722 eyes treated for myopia and myopic astigmatism.

    PubMed

    Hansen, Rasmus Søgaard; Lyhne, Niels; Grauslund, Jakob; Vestergaard, Anders Højslet

    2016-02-01

    To study the outcomes of small-incision lenticule extraction (SMILE) for treatment of myopia and myopic astigmatism. Retrospective study of patients treated for myopia or myopic astigmatism with SMILE, using a VisuMax(®) femtosecond laser (Carl Zeiss Meditec, Jena, Germany), at the Department of Ophthalmology, Odense University Hospital, Odense, Denmark. Inclusion criteria were corrected distance visual acuity (CDVA) of 20/25 or better before surgery and no ocular conditions other than myopia up to -10.00 diopters (D) with astigmatism up to 3.00 D. Of the 729 treatments, 722 were included. The spherical equivalent (SE) refraction averaged -6.82 ± 1.66 diopters (D) before surgery. After 3 months, 88 % of eyes were within ±0.50 D of the intended refraction, whilst 98 % were within ±1.00 D. The mean difference between attempted and achieved SE refraction at 3 months after surgery was -0.06 ± 0.01 D (range: -1.25 to 1.25 D). In eyes with emmetropia as target refraction (n = 362), 63 % had uncorrected distance visual acuity (UDVA) of 20/25 or better 1 day after surgery, rising to 83 % at 3 months after surgery. The average gain in CDVA from before surgery to 3 months after surgery was 0.07 ± 0.03 (logMAR). However, 12 eyes (1.6 %) lost 2 or more lines of CDVA from before surgery to 3 months postoperatively. Simultaneous treatment of up to 3.00 D of astigmatism was not associated with less predictable refractive outcomes. In the short term, SMILE seemed predictable, efficient, and safe for treatment of myopia and myopic astigmatism.

  8. Surgically-induced astigmatism in combined ECCE with filtering procedures compared to ECCE alone.

    PubMed

    Choplin, N T; Monroe, J F

    1992-02-01

    Extracapsular cataract extraction with implantation of a posterior chamber lens combined with filtering surgery (glaucoma triple procedure) is frequently employed in the co-management of cataract and glaucoma. Nineteen triple procedures with a minimum of six months follow up were compared to 19 cases of extracapsular cataract extraction with lens implant matched for age, sex, and surgeon with regard to surgically induced astigmatism as determined by vector analysis. Follow up averaged 10 months for the triple group and 14 months for the controls. There was no statistically significant difference in preoperative astigmatism between the two groups nor in the mean number of sutures cut. Postoperatively, the keratometric cylinder averaged 2.55 +/- 1.54 diopters for the cases and 1.20 +/- 1.11 D for the controls; the difference of 1.36 D was statistically significant (P = .004). The postoperative refractive cylinder was 2.34 +/- 1.54 D for the cases and 1.29 +/- 1.07 D for the controls; the difference of 1.05 D was statistically significant (P = .017). With regard to surgically-induced astigmatism, vector analysis showed that the cases averaged 2.18 +/- 1.25 D and the controls 1.23 +/- 0.81 D; the difference of 0.95 D was statistically significant (P = .006). With regard to surgically-induced astigmatism, vector analysis showed that the cases averaged 2.18 +/- 1.25 D and the controls 1.23 +/- 0.81 D; the difference of 0.95 D was statistically significant (P = .006). When analyzed for change along the vertical meridian, the cases averaged 1.12 +/- 1.57 D surgically-induced against-the-rule astigmatism, as compared with 0.30 +/- 1.16 D for the controls (difference, 0.83 D; P = .062). The glaucoma triple procedures induced approximately 1.00 D more cylinder than the controls.

  9. Correction of irregular and induced regular corneal astigmatism with toric IOL after posterior segment surgery: a case series.

    PubMed

    Kolozsvári, Bence L; Losonczy, Gergely; Pásztor, Dorottya; Fodor, Mariann

    2017-01-13

    Toric intraocular lens (IOL) implantation can be an effective method for correcting corneal astigmatism in patients with vitreoretinal diseases and cataract. Our purpose is to report the outcome of toric IOL implantation in two cases - a patient with scleral-buckle-induced regular corneal astigmatism and a patient with keratoconus following pars plana vitrectomy. As far as we are aware, there are no reported cases of toric IOL implantation in a vitrectomized eye with keratoconus nor of toric IOL implantation in patients with scleral-buckle-induced regular corneal astigmatism. Two patients with myopia and high corneal astigmatism underwent cataract operation with toric IOL implantation after posterior segment surgery. Myopia and high astigmatism (>2.5 diopter) were caused by previous scleral buckling in one case and by keratoconus in the other case. Pre- and postoperative examinations during the follow-up of included uncorrected and spectacle corrected distance visual acuity (UCDVA/CDVA), automated kerato-refractometry (Topcon), Pentacam HR, IOL Master (Zeiss) axial length measurements and fundus optical coherence tomography (Zeiss). One year postoperatively, the UCDVA and CDVA were 20/25 and 20/20 in both cases, respectively. The absolute residual refractive astigmatism was 1.0 and 0.75 Diopters, respectively. The IOL rotation was within 3° in both eyes, therefore IOL repositioning was not necessary. Complications were not observed in our cases. These cases demonstrate that toric IOL implantation is a predictable and safe method for the correction of high corneal astigmatism in complicated cases with different origins. Irregular corneal astigmatism in keratoconus or scleral-buckle-induced regular astigmatisms can be equally well corrected with the use of toric IOL during cataract surgery. Previous scleral buckling or pars plana vitrectomy seem to have no impact on the success of the toric IOL implantation, even in keratoconus. IOL rotational stability and

  10. Safety and efficacy of femtosecond laser-assisted arcuate keratotomy to treat irregular astigmatism after penetrating keratoplasty.

    PubMed

    Fadlallah, Ali; Mehanna, Chadi; Saragoussi, Jean-Jacques; Chelala, Elias; Amari, Belkacem; Legeais, Jean-Marc

    2015-06-01

    To determine the refractive efficacy, predictability, stability, and complication rate of Intralase femtosecond laser-assisted astigmatic keratotomy (AK) for irregular astigmatism after penetrating keratoplasty (PKP). Ophthalmology Department, Hôtel-Dieu, Paris, France. Retrospective case series. Femtosecond laser-assisted AK was performed to treat high irregular astigmatism (>5.0 diopters [D]) after PKP. The uncorrected (UDVA) and corrected (CDVA) distance visual acuities, manifest refraction, vector analysis, and complications were evaluated. The study evaluated 62 eyes of 57 patients over a mean follow-up of 28 months ± 3.5 (SD). Preoperatively, the mean CDVA was 0.51 ± 0.26 logMAR and the mean UDVA was 0.98 ± 0.24 logMAR; 6 months postoperatively, the mean CDVA and UDVA improved to 0.40 ± 0.22 logMAR and 0.60 ± 0.2 logMAR, respectively (both P < .01). The mean preoperative absolute astigmatism was 7.1 ± 1.72 D; 6 months postoperatively, the mean refractive astigmatism was 2.6 ± 2.4 D (P < .001). The UDVA, CDVA, and astigmatism remained stable up to the end of follow-up. The efficacy index was 0.81 at 6 months and 0.67 at 2 years. There were 2 cases of microperforation, 3 cases of infectious keratitis, 3 graft rejection episodes, and 1 case of endophthalmitis. Overcorrection occurred in 12 eyes. Femtosecond laser-assisted AK was effective in reducing irregular astigmatism after PKP. Predictability of astigmatism correction is variable over time with a decrease in the efficacy index 2 years postoperatively. Refinement of the treatment nomogram for femtosecond laser-assisted AK for high astigmatism after PKP remains a major issue. No author has a financial or proprietary interest in any material or method mentioned. Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  11. Comparison of femtosecond laser small-incision lenticule extraction and laser-assisted subepithelial keratectomy to correct myopic astigmatism.

    PubMed

    Qian, Yishan; Huang, Jia; Zhou, Xingtao; Wang, Yutung

    2015-11-01

    To compare the efficacy of correcting myopic astigmatism with femtosecond laser small-incision lenticule extraction (SMILE, Carl Zeiss Meditec AG) versus laser-assisted subepithelial keratectomy (LASEK). The study was conducted at the Ophthalmology Department, Eye and ENT Hospital, Shanghai, China. A retrospective, cross-sectional study. This study included patients who underwent small-incision lenticule extraction or LASEK for the correction of myopia and myopic astigmatism. Preoperative and 6-month postoperative astigmatism values were analyzed. The efficacies of the 2 surgeries to correct astigmatism were compared. A total of 180 right eyes of 180 patients (small-incision lenticule extraction: n = 113, LASEK: n = 67) were included. No significant difference was found between the 2 groups in the preoperative astigmatism (small-incision lenticule extraction: 1.16 ± 0.85D, LASEK: 1.16 ± 0.83D, P > .05) or the postoperative astigmatism (small-incision lenticule extraction: 0.35 ± 0.37D; LASEK: 0.31 ± 0.42D, P > .05), determined by manifest refraction. No significant difference was found between the 2 groups in surgically induced astigmatism vector (small-incision lenticule extraction: 1.13 ± 0.83D, LASEK: 1.01 ± 0.65D, P > .05). The correction index was higher for the small-incision lenticule extraction group (1.05 ± 0.53) than for the LASEK group (0.95 ± 0.21, P = .045). The postoperative astigmatism was significantly higher for the small-incision lenticule extraction group when the preoperative astigmatism was 1.0 D or less (small-incision lenticule extraction: 0.26 ± 0.30D, LASEK: 0.12 ± 0.20D, P = .007) and lower for the small-incision lenticule extraction group when the preoperative astigmatism was more than 2.0 D (small-incision lenticule extraction: 0.48 ± 0.37D, LASEK: 0.89 ± 0.46D, P = .002). An adjustment of nomograms for correcting low astigmatism (≤1.0 D) by small-incision lenticule extraction is suggested due to the tendency toward

  12. Corneal Diameter as a Factor Influencing Corneal Astigmatism After Cataract Surgery.

    PubMed

    Theodoulidou, Sofia; Asproudis, Ioannis; Kalogeropoulos, Christos; Athanasiadis, Aristidis; Aspiotis, Miltiadis

    2016-01-01

    To evaluate the corneal horizontal diameter [white-to-white (WTW) distance] as a factor influencing surgically induced astigmatism (SIA) and postoperative astigmatism. A total of 330 eyes with corneal astigmatism ≤1.5 D underwent cataract surgery with phacoemulsification. A 3-step, superotemporal for the right eye and superonasal for the left eye, clear corneal incision of 3.0 mm was made. Four groups were created according to WTW distance: group A ≤11.6 mm, group B 11.7 to 11.9 mm, group C 12.0 to 12.2 mm, and group D ≥12.3 mm. SIA was calculated by vector analysis using the Alpins method. We noted all cases, in which a change greater than 0.5 diopters (D) in astigmatism took place and a change greater than 20 degrees in axis torque, despite axis direction, on the first and sixth postoperative months. SIA was found in group A 0.98 D ± 0.6 (SD), B 0.79 D ± 0.43 (SD), C 0.68 D ± 0.45 (SD), and D 0.53 D ± 0.32 (SD) at the first postoperative month. At the sixth postoperative month, SIA was 0.77 D ± 0.43 (SD), 0.69 D ± 0.34 (SD), 0.62 ± 0.36 (SD), and 0.49 D ± 0.27 (SD), respectively. A change greater than 0.5 D in corneal astigmatic power at the first and sixth months postoperatively was significantly lower in eyes with WTW distance 12.0 to 12.2 mm and ≥12.3 mm in comparison with eyes with WTW distance ≤11.6 mm and 11.7 to 11.9 mm (P < 0.05). Changes greater than 20 degrees in astigmatic axis at the first and sixth postoperative months were not significantly different according to the horizontal corneal diameter. WTW distance should always be measured preoperatively when planning cataract surgery and should be accounted for in cases of large and small corneas.

  13. Extended depth of focus intra-ocular lens: a solution for presbyopia and astigmatism

    NASA Astrophysics Data System (ADS)

    Zlotnik, Alex; Raveh, Ido; Ben Yaish, Shai; Yehezkel, Oren; Belkin, Michael; Zalevsky, Zeev

    2010-02-01

    Purpose: Subjects after cataract removal and intra-ocular lens (IOL) implantation lose their accommodation capability and are left with a monofocal visual system. The IOL refraction and the precision of the surgery determine the focal distance and amount of astigmatic aberrations. We present a design, simulations and experimental bench testing of a novel, non-diffractive, non-multifocal, extended depth of focus (EDOF) technology incorporated into an IOL that allows the subject to have astigmatic and chromatic aberrations-free continuous focusing ability from 35cm to infinity as well as increased tolerance to IOL decentration. Methods: The EDOF element was engraved on a surface of a monofocal rigid IOL as a series of shallow (less than one micron deep) concentric grooves around the optical axis. These grooves create an interference pattern extending the focus from a point to a length of about one mm providing a depth of focus of 3.00D (D stands for Diopters) with negligible loss of energy at any point of the focus while significantly reducing the astigmatic aberration of the eye and that generated during the IOL implantation. The EDOF IOL was tested on an optical bench simulating the eye model. In the experimental testing we have explored the characteristics of the obtained EDOF capability, the tolerance to astigmatic aberrations and decentration. Results: The performance of the proposed IOL was tested for pupil diameters of 2 to 5mm and for various spectral illuminations. The MTF charts demonstrate uniform performance of the lens for up to 3.00D at various illumination wavelengths and pupil diameters while preserving a continuous contrast of above 25% for spatial frequencies of up to 25 cycles/mm. Capability of correcting astigmatism of up to 1.00D was measured. Conclusions: The proposed EDOF IOL technology was tested by numerical simulations as well as experimentally characterized on an optical bench. The new lens is capable of solving presbyopia and astigmatism

  14. Characteristics of Corneal Astigmatism of Anterior and Posterior Surface in a Normal Control Group and Patients With Keratoconus.

    PubMed

    Shajari, Mehdi; Friderich, Stefan; Pour Sadeghian, Miad; Schmack, Ingo; Kohnen, Thomas

    2017-04-01

    To evaluate and compare power and axis orientation of anterior and posterior astigmatism in eyes with keratoconus with healthy eyes. In this retrospective cohort study, we examined 861 eyes of 494 patients diagnosed with keratoconus at the Department of Ophthalmology, University Hospital Frankfurt, and 256 eyes of 256 healthy individuals. Using a Scheimpflug device (Pentacam HR), we measured the magnitude and axis orientation of anterior and posterior corneal astigmatism, corneal thickness, and conus location. The results were compared between different stages of the disease according to the Amsler-Krumeich classification and the control group. Magnitude of corneal astigmatism was 3.47 ± 2.10 diopters (D) on the anterior surface and 0.69  ± 0.40 D on the posterior surface in eyes across all keratoconus stages. We found a significant increase of anterior and posterior corneal astigmatism with progression of disease (P < 0.01, 1-way analysis of variance) and a significant correlation between anterior and posterior corneal astigmatism (r = 0.77, P < 0.01). In contrast to eyes of healthy individuals, in which posterior corneal axis alignment is vertical in most cases independent of anterior alignment, we found in eyes with keratoconus a match between anterior and posterior alignment when alignment was vertical in 97% of eyes, 46% when oblique and 61% when horizontal (Cohen kappa coefficient κ = 0.55, P < 0.01). With progression of disease, alignment of anterior and posterior corneal astigmatism became increasingly vertical. In eyes with keratoconus, posterior axis alignment of corneal astigmatism is in line with alignment of the anterior surface in the majority of cases. Posterior astigmatism axis alignment could potentially be used in algorithms to support diagnosis and staging of keratoconus.

  15. Visual acuity and astigmatism in periocular infantile hemangiomas treated with oral beta-blocker versus intralesional corticosteroid injection.

    PubMed

    Herlihy, Erin P; Kelly, John P; Sidbury, Robert; Perkins, Jonathan A; Weiss, Avery H

    2016-02-01

    Periocular infantile hemangiomas (PIH) can induce anisometropic astigmatism, a risk factor for amblyopia. Oral beta-blocker therapy has largely supplanted systemic or intralesional corticosteroids. The purpose of this study was to evaluate the effect and time course of these treatment modalities on visual acuity and induced astigmatism. The medical records of patients with PIH treated with oral propanolol between November 2008 and July 2013 were retrospectively reviewed for data on visual acuity and astigmatism. Patients with incomplete pre- and post-treatment ophthalmic examinations were excluded. Results were compared to those of a similar cohort treated with intralesional corticosteroid injection. Mean astigmatism in affected eyes was 1.90 D before propranolol and 1.00 D after; patients showed a monophasic reduction in astigmatism over 12 months. By comparison, patients treated with corticosteroid injection showed a biphasic response, with an immediate steep decrease followed by a slow monophasic decline, paralleling propranolol-treated patients. Oral propranolol treatment caused a 47% reduction in mean induced astigmatism, less than the 63% reduction reported for the cohort treated with corticosteroid. No patient had visual acuity in the affected eye more than 1 standard devation below the age-matched norm, and none experienced significant side effects when treated with oral propranolol. In this patient cohort oral beta-blocker was well-tolerated. Treatment was therefore often initiated prior to the induction of significant astigmatism, with treatment effects comparable to steroid treatment. Visual outcomes were good. Early treatment may minimize the potential effect of astigmatism on postnatal visual development. Copyright © 2016 American Association for Pediatric Ophthalmology and Strabismus. Published by Elsevier Inc. All rights reserved.

  16. Risk Factors for Astigmatism in Preschool Children: The Multi-Ethnic Pediatric Eye Disease and Baltimore Pediatric Eye Disease Studies

    PubMed Central

    Tarczy-Hornoch, Kristina; Varma, Rohit; Cotter, Susan A.; McKean-Cowdin, Roberta; Lin, Jesse H.; Borchert, Mark S.; Torres, Mina; Wen, Ge; Azen, Stanley P.; Tielsch, James M.; Friedman, David S.; Repka, Michael X.; Katz, Joanne; Giordano, Lydia; Ibironke, Josephine

    2011-01-01

    Objective To evaluate risk factors for astigmatism in a population-based sample of preschool children. Design Population-based cross-sectional study Participants Population-based samples of 9970 children ages 6 to 72 months from Los Angeles County, California, and Baltimore, Maryland. Methods A cross-sectional study of children participating in the Multiethnic Pediatric Eye Disease Study and the Baltimore Eye Disease Study was completed. Data were obtained by clinical examination or by in-person interview. Odds ratios and 95% confidence intervals (95%CI) were calculated to evaluate potential associations between clinical, behavioral, or demographic factors and astigmatism. Main Outcome Measures Odds ratios (ORs) for various risk factors associated with astigmatism. Results Participants with myopia (≤−1.0 diopters) were 4.6 times more likely to have astigmatism (95%CI 3.56, 5.96) than those without refractive error, while participants with hyperopia (≥+2.00 diopters) were 1.6 times more likely (95%CI 1.39, 1.94). Children 6 months to <12 months of age were approximately 3 times more likely to have astigmatism than children 5 to 6 years of age (95%CI 2.28, 3.73). Both Hispanic (OR=2.38) and African-American (OR=1.47) children were more likely to have astigmatism than non-Hispanic white children. Further, children whose mothers smoked during pregnancy were 1.46 times (95% CI 1.14, 1.87) more likely to have astigmatism than children whose mothers did not smoke. Conclusions In addition to infancy, Hispanic and African-American race/ethnicity and correctable/modifiable risk factors such as myopia, hyperopia, and maternal smoking during pregnancy are associated with a higher risk of having astigmatism. While the prevalence of smoking during pregnancy is typically low, this association may suggest etiologic pathways for future investigation. PMID:21856010

  17. The Effects of Surgical Factors on Postoperative Astigmatism in Patients Enrolled in the Infant Aphakia Treatment Study (IATS)

    PubMed Central

    Wall, Palak B.; Lee, Jason A.; Lynn, Michael; Lambert, Scott R.; Traboulsi, Elias I.

    2015-01-01

    Purpose To evaluate the impact of surgical factors such as incision type, number of sutures, and technique of closure on postoperative astigmatism in infants undergoing cataract extraction with or without intraocular lens implantation. Methods The IATS is a multicenter (n=12) clinical trial in which 114 infants with unilateral congenital cataracts were randomized to undergo cataract extraction with intraocular lens (IOL) placement or contact lens aphakic correction. Surgical videos were reviewed with regard to incision type and location, whether the incision was extended, the number of sutures placed, and technique of closure. Corneal astigmatism was measured using a handheld keratometer prior to surgery and at 1 year of age. Results Corneal astigmatism decreased from a mean of 1.92 D at baseline to 1.62 D at age 1 year in the CL group, but remained almost unchanged from 2.00 D to 2.09 D in the IOL group (p=0.023). There was no statistical difference between the amount of corneal astigmatism irrespective of incision type (p=0.214) and no increase in astigmatism with extension of the incision to facilitate IOL placement (p=0.849) at 1 year. The number of sutures and technique of closure did not influence the amount of astigmatism at 1 year. Conclusions At the age of one year following cataract extraction in infants, contact lens correction and the lack of IOL placement are associated with a significant decrease in postoperative corneal astigmatism compared to intraocular lens placement. No other surgical factors considered in this study had a statistically significant impact on corneal astigmatism. PMID:25266831

  18. Fourier analysis of induced irregular astigmatism. Photorefractive keratectomy versus laser in situ keratomileusis in a bilateral cohort of hyperopic patients.

    PubMed

    Sciscio, Andrea; Hull, Christopher C; Stephenson, Chris G; Baldwin, Heather; O'Brart, David; Marshall, John

    2003-09-01

    To analyze corneal topographic data by Fourier analysis to determine differences in irregular astigmatism following spherical hyperopic correction by photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK). Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom. Thirty-six eyes of 18 patients with moderate hyperopia had LASIK in 1 eye and PRK in the other eye. The flap was cut on a nasal hinge with a Moria LSK One microkeratome. The laser was a Summit SVS Apex Plus with an optical zone of 6.5 mm and a blending zone of 1.5 mm. Corneal topographic data were acquired with a TMS-1 topographer (Computed Anatomy Inc.) preoperatively and 1, 3, 6, and 12 months postoperatively. The ASCII files containing the dioptric power values were extracted and analyzed with custom-written software to extract the Fourier harmonics. The irregular astigmatism increased in both groups postoperatively, peaking at 3 months and then decreasing over the next 9 months. There was no statistically significant difference between the 2 groups at any time point (P<.05). The change in the topographically derived equivalent sphere showed undercorrection in both groups at all time points. Regular astigmatism showed a marginal statistically significant increase in the LASIK group at 12 months (P =.049). Irregular astigmatism, equivalent sphere, and regular astigmatism were not significantly different in the PRK and LASIK groups during the follow-up. Based on the corneal topography, the 2 procedures induced an equal amount of irregular astigmatism.

  19. Corneal topographic changes and surgically induced astigmatism following combined phacoemulsification and 25-gauge vitrectomy

    PubMed Central

    Sayed, Khulood Mohammed; Farouk, Mahmoud M.; Katome, Takashi; Nagasawa, Toshihiko; Naito, Takeshi; Mitamura, Yoshinori

    2017-01-01

    AIM To evaluate corneal topographic changes and surgically induced astigmatism (SIA) after combined phacoemulsification and 25-gauge transconjunctival sutureless vitrectomy (25-G TSV). METHODS A retrospective study on 96 eyes of 87 patients who underwent combined phacoemulsification and 25-G TSV. The different topographic parameters and SIA were analyzed pre- and postoperatively. RESULTS There was no significant changes in corneal topographic parameters at different follow up periods. Only surface regularity index changed significantly in the 2nd postoperative week and then returned to baseline values thereafter. Mean SIA gradually decreased to reach 0.12 D by the 6th postoperative month. CONCLUSION Corneal surface and astigmatic changes are insignificant in either early or late postoperative periods following combined phacoemulsification and 25-G TSV. The SIA was the minimum among previous reports on sutureless vitrectomy alone or combined with phacoemulsification. Improvement of SIA did not stop at the 3rd postoperative month but it continued till the 6th month postoperatively. PMID:28149780

  20. Astigmatism and spontaneous emission factor of laser diodes with parabolic gain

    SciTech Connect

    Mamine, T.

    1983-04-01

    An explicit relation between the astigmatism and the spontaneous emission factor of gain guiding lasers has been derived with the assumption that the gain profile can be approximated to be a parabola or that the lowest order mode in the cavity is approximately Gaussian. The maximum value of the spontaneous emission factor is shown to be ..sqrt..2 if index guiding is dominant. Beyond K = ..sqrt..2, where gain guiding is dominant in this region, the astigmatism decreases with the spontaneous emission factor. It is also shown that the spontaneous emission factor of the gain guiding lasers does not much exceed ten and this conclusion has been confirmed experimentally for those whose stripe widths are larger than 4 ..mu..m.

  1. Mode coupling enhancement by astigmatism compensation in a femtosecond laser cavity

    NASA Astrophysics Data System (ADS)

    Castro-Olvera, Gustavo; Garduño-Mejía, Jesus; Rosete-Aguilar, Martha; Roman-Moreno, Carlos J.

    2016-09-01

    In this work we present a numerical analysis of the mode coupling between the pump-beam and the laser-beam in a Ti:Sapphire crystal used as a gain medium of a femtosecond laser. Using the Matrix ABCD and propagation gaussian beam models, we obtained an optimal configuration for compensate the astigmatism in the output beam laser. Also we analysed pump-beam propagation and got the settings to fix the astigmatism in the crystal. Furthermore we apply this configuration to a homemade femtosecond laser, accomplishing an overall efficiency of laser to 20% in continuum wave (CW) and 16% in mode looking (ML) operation. The femtosecond laser have 30 nm bandwidth to FWHM at 810 nm corresponding 30fs.

  2. Autorefraction, Retinoscopy, Javal's Rule, and Grosvenor's Modified Javal's Rule: The Best Predictor of Refractive Astigmatism

    PubMed Central

    Asiedu, Kofi; Ampiah, Emmanuel Ekow

    2016-01-01

    The aim of the study was to determine the level of agreement between Javal's rule, autorefraction, retinoscopy, and refractive astigmatism and to determine which technique is the most suitable substitute when subjective refraction is not applicable using a clinical sample. A total of 36 subjects, 14 males and 22 females, were involved in this study. The intraclass correlation coefficients between subjective refraction, autorefraction, and retinoscopy were 0.895 and 0.989, respectively, for the spherical equivalent. The Bland-Altman 95% limits of agreement between subjective refraction and autorefraction; subjective refraction and retinoscopy; and autorefraction and retinoscopy were −2.84 to 3.58, −0.88 to 1.12, and −3.01 to 3.53, respectively, for the spherical equivalent. The intraclass correlation coefficients between spectacle total astigmatism and the following techniques were as follows: retinoscopy (0.85); autorefraction (0.92); Javal's rule (0.82); and Grosvenor et al. version (0.85). The Bland-Altman 95% limits of agreement between subjective refraction and autorefraction; subjective refraction and retinoscopy; subjective refraction and Javal's rule; and subjective refraction and Grosvenor et al. version were −0.87 to 1.25, −1.49 to 1.99, −0.73 to 1.93, and −0.89 to 1.7, respectively, for the total astigmatism. The study showed that autorefraction and Javal's rule may provide a starting point for subjective refraction cylinder power determination but only retinoscopy may satisfactorily replace subjective refraction total astigmatism when subjective refraction is not applicable. PMID:27803811

  3. Corneo-scleral contact lenses in an uncommon case of keratoconus with high hyperopia and astigmatism.

    PubMed

    Porcar, Esteban; Montalt, Juan Carlos; España-Gregori, Enrique; Peris-Martínez, Cristina

    2017-10-01

    To analyse the visual quality achieved by fitting corneo-scleral contact lenses (CScL) in an uncommon case of bilateral keratoconus, high hyperopia and astigmatism. A 45-year-old man presented for eye examination due to the unsatisfactory quality of his vision wearing soft toric contact lenses. He presented high hyperopia and astigmatism with bilateral keratoconus. He was fitted with CScL to correct his irregular astigmatism and ocular aberrations. A diagnostic trial set was used in the fitting process and he was assessed according to standardised fitting methodology. Visual acuity, corneal topography, biometry and ocular aberrations were evaluated. The follow-up period was 1year. The best spectacle-corrected visual acuity was 20/32 with +8.00/-4.50×30° for the right eye (RE) and 20/25 with +7.75/-2.25×120° for the left eye (LE). After CScL fitting, visual acuity was improved to 20/20 and 20/16 for the RE and LE, respectively. The patient wore these contact lenses an average of 13h a day. The total high order aberrations decreased by approximately 79% in the RE (2.37-0.50μm) and 47% in the LE (1.04-0.55μm) after CScL fitting. Visual quality and wearing time were maintained after 1year wearing CScL. In addition, no adverse ocular effects were found during this period. The present case report describes how the patient had CScL fitted successfully for management of keratoconus with high hyperopia and astigmatism. They provided optimal visual quality, along with prolonged use times and no adverse effects to the cornea. Copyright © 2017 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

  4. Astigmatism and defocus wavefront correction via Zernike modes produced with fluidic lenses

    PubMed Central

    Marks, Randall; Mathine, David L.; Schwiegerling, Jim; Peyman, Gholam; Peyghambarian, Nasser

    2010-01-01

    Fluidic lenses have been developed for ophthalmic applications with continuously varying optical powers for second order Zernike modes. Continuously varying corrections for both myopic and hyperopic defocus have been demonstrated over a range of three diopters using a fluidic lens with a circular retaining aperture. Likewise, a six diopter range of astigmatism has been continuously corrected using fluidic lenses with rectangular apertures. Imaging results have been characterized using a model eye. PMID:19571912

  5. [Evaluation of astigmatism and blood-aqueous barrier breakdown following procedures in the anterior eye segment].

    PubMed

    Zarnowski, T; Chmiel, M; Haszcz, D; Zagórski, Z

    1998-01-01

    The aim of this study was to evaluate the disruption of the blood-aqueous barrier (BAB) and the induced astigmatism following phacoemulsification, trabeculectomy and phacotrabeculectomy. 141 eyes of patients who underwent different surgical procedures of the anterior segment were examined with the use of computer-assisted videokeratography. All maps were recorded preoperatively, and one and five days after surgery. We also applied a laser flare-meter in 41 eyes in order to quantify aqueous flare following these procedures. The mean surgically-induced astigmatism following conventional trabeculectomy was 2.1 D and 1.4 D one and five days postoperatively, phacoemulsification with sutures 2.7 D and 1.9 D and phacotrabeculectomy 3.0 D and 2.4 D, respectively. Lower values of astigmatism obtained after sutureless phacoemulsification were 0.6 D and 0.3 D one and five days postoperatively, respectively (p < 0.05 vs Phaco+IOL+Trab. group, p < 0.01 vs other groups). It was found that aqueous flare values following phacotrabeculectomy were 58.0 photon counts/milisec.--one day, 39.3--3 days, 24.4--7 days, 20.4--10 days postoperatively. Significantly reduced values were observed after phacoemulsification--27.6 one day after surgery and 17.6--3 days later (p < 0.01 vs Phaco+IOL+Trab.group). It could be concluded that induced astigmatism and the amount of inflammation were the highest after triple procedure and the lowest after phacoemulsification.

  6. Distribution of Anterior and Posterior Corneal Astigmatism in Eyes With Keratoconus.

    PubMed

    Naderan, Mohammad; Rajabi, Mohammad Taher; Zarrinbakhsh, Parviz

    2016-07-01

    To investigate the magnitude, with-the-rule (WTR) or against-the-rule (ATR) orientation, and vector components (Jackson astigmatic vectors [J0 and J45] and blurring strength) of the anterior and posterior corneal astigmatism (ACA and PCA) in patients with keratoconus (KC) in a retrospective study, and to try to find suitable cutoff points for ACA and PCA in an attempt to discriminate KC from normal corneas. Retrospective age- and sex-matched case-control study. Using the Pentacam images, the aforementioned parameters were compared between 1273 patients with KC and 1035 normal participants. The mean magnitude of the ACA and PCA was 4.49 ± 2.16 diopter (D) and 0.90 ± 0.43 D, respectively. The dominant astigmatism orientation of the ACA was ATR in KC patients and WTR in normal participants (P < .001), while for the PCA it was WTR in KC patients and ATR in normal participants (P < .001). There was a significant agreement between the axis orientations of ACA and PCA in KC patients (ĸ = 0.077, P < .001), but not in the normal group (P = .626). ACA and PCA magnitude, M, J0, J45, and blur significantly increased by increasing KC severity. There was a trend for increasing anterior ATR and posterior WTR, and decreasing oblique astigmatism on both corneal surfaces by increasing the KC severity according to the Amsler-Krumeich classification. A cutoff value of 1.8 D for ACA had 90.2% sensitivity and specificity, and that of 0.4 D for PCA had 89.5% sensitivity and 85.0% specificity for discriminating KC from normal corneas. Our findings can help clinicians in the diagnosis of KC and lens manufacturers in designing suitable contact or intraocular lenses. Copyright © 2016 Elsevier Inc. All rights reserved.

  7. Effectiveness of Toric Orthokeratology in the Treatment of Patients with Combined Myopia and Astigmatism.

    PubMed

    Lyu, Byul; Hwang, Kyu Yeon; Kim, Sun Young; Kim, Su Young; Na, Kyung Sun

    2016-12-01

    The purpose of this multi-institute, single-group clinical trial was to evaluate the effectiveness and safety of toric orthokeratology lenses for the treatment of patients with combined myopia and astigmatism. A total of 44 patients were included in this clinical trial. The patients ranged in age from 7 to 49 years, with myopia of -0.75 to -6.0 diopters (D) and astigmatism of 1.25 to 4.0 D. After excluding 21 subjects, 23 subjects (39 eyes) were analyzed after toric orthokeratology lens use. The subjects underwent ophthalmologic examination after 1 day and 1, 2, 3, and 4 weeks of wearing overnight toric orthokeratology lenses. A total of 19 subjects (31 eyes) completed the trial after five subjects (eight eyes) dropped out. In the patients who completed the study by wearing lenses for 4 weeks, the myopic refractive error decreased significantly by 2.60 ± 2.21 D (p < 0.001), from -3.65 ± 1.62 to -1.05 ± 1.64 D. The astigmatic refractive error were also significantly decreased by 0.63 ± 0.98 D (p = 0.001), from 2.07 ± 0.83 to 1.44 ± 0.99 D. The mean uncorrected and corrected visual acuities before wearing the lenses were 2.14 ± 0.80 logarithm of the logMAR (logMAR) and 0.05 ± 0.13 logMAR, respectively, which changed to 0.12 ± 0.30 logarithm of the logMAR (p < 0.001) and 0.01 ± 0.04 logMAR (p = 0.156) after 4 weeks. No serious adverse reactions were reported during the clinical trial. Our results suggest that toric orthokeratology is an effective and safe treatment for correcting visual acuity in patients with combined myopia and astigmatism.

  8. Wound stability and surgically induced corneal astigmatism after transconjunctival single-plane sclerocorneal incision cataract surgery.

    PubMed

    Hayashi, Ken; Ogawa, Soichiro; Yoshida, Motoaki; Yoshimura, Koichi

    2017-01-01

    To compare intraocular pressure (IOP) immediately after cataract surgery, and surgically induced corneal astigmatism (SIA) and corneal shape changes between eyes with transconjunctival single-plane sclerocorneal incisions (TSSIs) and eyes with clear corneal incisions (CCIs). Bilateral eyes of 64 patients undergoing phacoemulsification were randomized to undergo 2.4-mm temporal TSSI or CCI. IOP was measured preoperatively, and in the immediate postoperative periods. SIA was determined using vector analysis, and corneal shape changes and irregular astigmatism were evaluated using a videokeratography preoperatively, and in the early postoperative periods. Wound hydration was performed in 23 eyes (35.9 %) of the TSSI group and in 60 (93.8 %) of the CCI group (P < 0.0001). Mean IOP was significantly higher in the TSSI group than in the CCI group at 30, 60, and 120 min postoperatively (P ≤ 0.0179). SIA tended to be smaller in the TSSI group than the CCI group, but the difference was not significant. The higher order irregular astigmatism was smaller in the TSSI group than in the CCI group at 2 days (P = 0.0312). The videokeratography revealed a wound-related flattening postoperatively in both groups; this change disappeared within 4 weeks in the TSSI group, whereas it persisted until 12 weeks in the CCI group. IOP was significantly higher immediately after TSSI than after CCI and required less wound hydration, suggesting better stability with TSSI. Higher order irregular astigmatism and wound-related corneal flattening were smaller after TSSI than after CCI in the early periods, suggesting that fewer corneal shape changes with TSSI.

  9. Astigmatic wavefront correction of a gain-guided laser-diode array using anamorphic diffractive microlenses

    SciTech Connect

    Leger, J.R.; Scott, M.L.; Bundman, P.; Griswold, M.P.

    1988-01-01

    A diffractive microlens array was used to collimate a one-dimensional array of gain-guided AlGaAs lasers. The astigmatism of the lasers was removed by using anamorphic microlenses. The Strehl ratio of the resulting wavefront was 0.98. The microlens array was placed in an external cavity to produce a single coherent diffraction-limited beam from the AlGaAs laser array.

  10. CONTROL OF LASER RADIATION PARAMETERS: Simple scheme for the astigmatic transformation of laser modes

    NASA Astrophysics Data System (ADS)

    Malyutin, A. A.

    2003-11-01

    A simple astigmatic scheme for obtaining focused Laguerre—Gaussian beams upon the π/2 conversion of Hermite—Gaussian radiation modes is described. A zone in the vicinity of the focal region of a lens is estimated where the beam satisfies the conditions for the capture and confinement of microparticles. It is shown that this optical scheme uses the fractional Fourier transform, whose application in the π/2 converter is demonstrated for the first time.

  11. Effectiveness of Toric Orthokeratology in the Treatment of Patients with Combined Myopia and Astigmatism

    PubMed Central

    Lyu, Byul; Hwang, Kyu Yeon; Kim, Sun Young; Kim, Su Young

    2016-01-01

    Purpose The purpose of this multi-institute, single-group clinical trial was to evaluate the effectiveness and safety of toric orthokeratology lenses for the treatment of patients with combined myopia and astigmatism. Methods A total of 44 patients were included in this clinical trial. The patients ranged in age from 7 to 49 years, with myopia of -0.75 to -6.0 diopters (D) and astigmatism of 1.25 to 4.0 D. After excluding 21 subjects, 23 subjects (39 eyes) were analyzed after toric orthokeratology lens use. The subjects underwent ophthalmologic examination after 1 day and 1, 2, 3, and 4 weeks of wearing overnight toric orthokeratology lenses. Results A total of 19 subjects (31 eyes) completed the trial after five subjects (eight eyes) dropped out. In the patients who completed the study by wearing lenses for 4 weeks, the myopic refractive error decreased significantly by 2.60 ± 2.21 D (p < 0.001), from -3.65 ± 1.62 to -1.05 ± 1.64 D. The astigmatic refractive error were also significantly decreased by 0.63 ± 0.98 D (p = 0.001), from 2.07 ± 0.83 to 1.44 ± 0.99 D. The mean uncorrected and corrected visual acuities before wearing the lenses were 2.14 ± 0.80 logarithm of the logMAR (logMAR) and 0.05 ± 0.13 logMAR, respectively, which changed to 0.12 ± 0.30 logarithm of the logMAR (p < 0.001) and 0.01 ± 0.04 logMAR (p = 0.156) after 4 weeks. No serious adverse reactions were reported during the clinical trial. Conclusions Our results suggest that toric orthokeratology is an effective and safe treatment for correcting visual acuity in patients with combined myopia and astigmatism. PMID:27980362

  12. Treatment of mixed astigmatism: early clinical outcomes withWaveLight and Technolas excimer lasers.

    PubMed

    Kilavuzoğlu, Ayşe Ebru; Gönen, Tansu; Çelebi, Ali Rıza Cenk; Coşar Yurteri, Cemile Banu; Şener, Asım Bozkurt

    2016-04-19

    We aimed to compare the results of WaveLight Allegretto Wave Eye-Q 400 Hz and Technolas 217z100 excimer lasers in the treatment of mixed astigmatism. Forty-nine patients who underwent laser in situ keratomileusis for mixed astigmatism were included in this retrospective study. Twenty-eight eyes of 21 patients were treated with WaveLight and 46 eyes of 28 patients were treated with the Technolas excimer laser. The patients' visual acuities and refractive values were evaluated on postoperative day 1 and at 1 and 3 months. In the WaveLight and Technolas groups, cylindrical refractive errors at month 3 were -0.92 ± 0.28 D and -0.88 ± 0.46 D, respectively. Spherical equivalent values for the groups at month 3 were -0.38 ± 0.73 D and -0.33 ± 0.20 D, respectively. There was no significant difference in postoperative uncorrected distance visual acuity at month 3 between the two groups (P = 0.671). At postoperative month 3, 70% of patients treated with WaveLight and 100% of patients treated with Technolas had an uncorrected distance visual acuity of 20/25 or better (P = 0.211). There were no significant differences in refraction and visual acuity between the WaveLight and Technolas groups during a 3-month follow-up period after laser in situ keratomileusis for mixed astigmatism.

  13. Inadequacy of a polyester (Mersilene) suture for the reduction of astigmatism after penetrating keratoplasty.

    PubMed Central

    Bertram, B A; Drews, C; Gemmill, M; Guell, J; Murad, M; Waring, G O

    1990-01-01

    Through two prospective studies, we evaluated the use of polyester (Mersilene) sutures in penetrating keratoplasty. Study 1 was a randomized comparison of combined running and interrupted Mersilene and nylon sutures (n = 45). Study 2 was a case series of single running Mersilene with postoperative adjustment of suture tension to manage astigmatism (n = 23). Study 1 demonstrated that Mersilene interrupted sutures were 5.5 times more likely to have handling-related complications compared to nylon (P = 0.01); in addition, they were 3 times as likely to have tissue-related complications as nylon interrupted sutures (P = 0.16). Study 2 demonstrated a complication rate of 69% when Mersilene was used as a single adjustable running suture. At 6 months postoperatively, the median refractive astigmatism for the adjustable cases was 3.37 D (mean, 4.03 +/- 2.37 D). Eyes in Study 2 with significant suture-related complications were 2.85 times more likely to have greater than 4 D of refractive astigmatism than were eyes without suture-related complications. We concluded that Mersilene is an undesirable suture for use in penetrating keratoplasty. PMID:2095023

  14. Laser in situ keratomileusis for myopia and astigmatism: 6 month results.

    PubMed

    Dulaney, D D; Barnet, R W; Perkins, S A; Kezirian, G M

    1998-06-01

    To evaluate the visual and refractive results of laser in situ keratomileusis (LASIK) for mild to moderate myopia with or without astigmatism. Barnet-Dulaney Eye Center, Phoenix, Arizona, USA. Data were prospectively collected on 124 consecutive eyes having LASIK over 12 weeks. Eyes with a preoperative spherical equivalent (SE) from -1.35 to -10.00 diopters (D) (mean -4.81 D +/- 2.21 [SD]) and cylinder from 0 to 5.00 D (mean 1.12 +/- 1.12 D) were entered in the study. Thirty-one eyes had spherical corrections. Ninety-three eyes had spherocylinder corrections; preoperative astigmatism in these eyes ranged from 0.50 to 5.00 D (mean 1.47 +/- 1.09 D). Surgery included creation of a corneal flap using an automated microkeratome with a 160 microns plate followed by photoablation on the exposed stromal bed. Photoablation was performed using five zones varying from 5.0 to 6.6 mm in eyes with 6.25 D of myopia or less and with five passes at a 5.0 mm zone in eyes with 6.50 D of myopia or more. Astigmatism was corrected using a single-pass ablation through a 6.0 mm slit of varying diameter. Six month follow-up was obtained in 89 eyes (72%). All eyes were completely re-epithelialized by the first postoperative day. Uncorrected visual acuity was 20/40 or better in 81% of eyes at 1 day and in 91% at 6 months. At 6 months, the mean SE was -0.35 +/- 0.77 D; 83% were within +/- 1.00 D of plano. Postoperative astigmatism in the 93 eyes having cylinder correction ranged from 0 to 1.22 D (mean 0.38 +/- 0.42 D). No eye lost more than two lines of best spectacle-corrected visual acuity. Three eyes (2%) required surgical intervention for cap problems. Visually significant corneal haze was not observed. In eyes with myopia with or without astigmatism, LASIK provided rapid visual recovery with satisfactory visual and refractive outcomes. The effect of LASIK on visual function (night glare, contrast sensitivity) awaits further study.

  15. Assessment of aberrations and visual quality differences between myopic and astigmatic eyes before and after contact lens application

    PubMed Central

    Demir, Mustafa; Kurna, Sevda Aydin; Sengor, Tomris; Atakan, Tugba Gencaga; Sahin, Tayfun

    2015-01-01

    OBJECTIVE: To evaluate the aberration and visual quality differences between myopic and astigmatic eyes before and after contact lens application by using corneal aberrometer and low- contrast sensitivity chart. METHODS: Eighty eyes of 40 patients were included in this study. Patients were divided into two groups as myopic (40 eyes, n=20) and astigmatic groups (40 eyes, n=20). We used aspheric Balafilcon A (Purevision and Purevision Toric Bausch&Lomb, Rochester, USA) lenses for each group. Corneal aberrations and low-contrast sensitivity values were measured and compared for each patient in both groups. RESULTS: There were no statistically significant differences between myopic and astigmatic groups when we compared low-contrast sensitivity values for both on- and off-eyes. Mean total higher-order aberration (HOA) values for off-eye, were 0.29±0.10 μm, and 0.33±0.10 μm for on-eye in the myopic group, while they were 0.42±0.14 μm in off-eye and 0.37±0.23 μm in on-eye in the astigmatic group. Off-eye mean coma, irregular astigmatism and total higher-order aberration RMS (root-mean-square) values were significantly higher in the astigmatic group compared to the myopic group (p=0.006, p=0.001, p=0.001) but mean on-eye RMS values were not. CONCLUSION: Myopic and astigmatic patients differ in terms of high-order aberrations and these differences cannot be equalized after contact lens application, but visual quality can be improved in both patients by using contact lenses. PMID:28058332

  16. Internal, corneal, and refractive astigmatism as prognostic factors for intrastromal corneal ring segment implantation in mild to moderate keratoconus.

    PubMed

    Peña-García, Pablo; Alió, Jorge L; Vega-Estrada, Alfredo; Barraquer, Rafael I

    2014-10-01

    To improve the predictability of the visual and refractive outcomes of intrastromal corneal ring segment (ICRS) implantation in keratoconus patients and highlight the importance of internal astigmatism and its relationship to corneal and refractive astigmatism as prognostic factors. Vissum Corporación, Alicante, and Centro de Oftalmología Barrquer, Barcelona, Spain. Retrospective case series. Visual, refractive, topographic, and aberrometric variables were evaluated in eyes having ICRS implantation. The eyes were divided into 2 groups according to the relative position of the keratometric axis and refractive axis; that is, coincident axis (0 degree ± 15 [SD]) or uncoincident axis. Internal astigmatism was calculated by vectorial analysis. The relationship between topographic astigmatism and refractive astigmatism was evaluated. The follow-up was 6 months. Of the 127 eyes evaluated, 79 had grade II keratoconus and 48 had grade I keratoconus. Statistically significant differences were found in the relative position of the refractive axis and keratometric axis (P=.017). Internal astigmatism had a significant correlation with the gain in visual acuity in patients with grade II keratoconus (r = -0.455, P=.0001). This relationship was less significant in patients with grade I keratoconus (r = -0.391, P=.021). The predictability of visual and refractive outcomes can be significantly increased in grade II keratoconus patients when the relative position of the keratometric and refractive axes; the internal, corneal, and refractive astigmatism; and their combinations are used as prognostic factors. No author has a financial or proprietary interest in any material or method mentioned. Copyright © 2014 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  17. Comprehensive profile of bilateral astigmatism: rule similarity and symmetry patterns of the axes in the fellow eyes.

    PubMed

    Asharlous, Amir; Khabazkhoob, Mehdi; Yekta, Abbasali; Hashemi, Hassan

    2017-01-01

    To study rule similarity (isorule or anisorule) and symmetry patterns of axes (direct and mirror) in bilateral astigmatism. Six years of data were collected from four ophthalmology clinics in Tehran. After applying the exclusion criteria (having eye disease or history of ocular surgery), final analyses were performed on data of 160 608 cases whose mean age was 39.2 ± 15.4 years (10-80 years) and 53.7% female. All subjects had autorefraction, retinoscopy, and subjective refraction data. Rule similarity was categorised as isorule (with, against or oblique astigmatism) if the orientation type in fellow eyes was the same and anisorule if they were different. The prevalence of isorule astigmatism was 82.9% and was similar in men and women (p = 0.44). The prevalence of isorule astigmatism decreased with age and increased with greater spherical ametropia (p < 0.001). The median of the absolute inter-ocular axis difference from exact symmetry was 10° under the mirror symmetry model (mirror axes). Under the direct symmetry model (equal axes), the median of the absolute inter-ocular axis difference was significantly higher, at 20° (p < 0.001). 16.4% and 10.8% had exact mirror and direct symmetry, respectively. In addition, 68.0% of cases with mirror symmetry and 47.1% with direct symmetry were within ±15 degrees of exact symmetry. The results of the present study showed that bilateral astigmatism was mostly isorule. Bilateral symmetry of the astigmatism axes was highly prevalent and mostly of the mirror pattern. High astigmatic cases showed better symmetry. © 2016 The Authors Ophthalmic & Physiological Optics © 2016 The College of Optometrists.

  18. Effects of corneal irregular astigmatism on visual acuity after conventional and femtosecond laser-assisted Descemet's stripping automated endothelial keratoplasty.

    PubMed

    Tomida, Daisuke; Yamaguchi, Takefumi; Ogawa, Akiko; Hirayama, Yumiko; Shimazaki-Den, Seika; Satake, Yoshiyuki; Shimazaki, Jun

    2015-07-01

    To compare short-term outcomes of Descemet's stripping automated endothelial keratoplasty (DSAEK) using a graft prepared with either a femtosecond laser or a microkeratome. Thirty-eight patients underwent DSAEK with grafts prepared with either a femtosecond laser (f-DSAEK; 21 eyes) or a microkeratome (m-DSAEK; 17 eyes). Visual acuity, endothelial cell density, regular astigmatism and irregular astigmatism were compared between the two groups preoperatively and at 1, 3, and 6 months post-operatively. Fourier analysis was conducted to calculate astigmatism of the anterior and posterior surfaces, and total cornea, using anterior segment optical coherence tomography (AS-OCT). Visual acuity (logMAR) improved from 1.20 ± 0.60 to 0.43 ± 0.25 after m-DSAEK (P < 0.001) and from 1.20 ± 0.57 to 0.77 ± 0.33 after f-DSAEK (P = 0.0028) at 6 months following DSAEK. Visual acuity after m-DSAEK was significantly better than after f-DSAEK at 1, 3, and 6 months (P < 0.05). AS-OCT corneal images revealed greater irregularities on the posterior surfaces of f-DSAEK grafts compared to m-DSAEK grafts. Irregular astigmatism of the total cornea and the posterior surface was significantly larger after f-DSAEK than after m-DSAEK, although there was no significant difference in irregular astigmatism of the anterior surface at 6 months. Postoperative visual acuity was significantly correlated with the postoperative irregular astigmatism of the total cornea (r = 0.6657 and P < 0.001) and the anterior (r = 0.416, P = 0.016) and posterior surfaces (r = 0.7046, P < 0.001). Visual outcomes after f-DSAEK were poor compared to conventional m-DSAEK due to an increase in irregular astigmatism caused by posterior surface irregularities.

  19. Apparent accommodation in pseudophakic eyes with refractive against-the-rule, with-the-rule and minimum astigmatism.

    PubMed

    Yamamoto, Toshiya; Hiraoka, Takahiro; Oshika, Tetsuro

    2016-04-01

    To compare the magnitude of apparent accommodation in pseudophakic eyes with refractive against-the-rule (ATR), with-the-rule (WTR) and minimum astigmatism. Factors associated with apparent accommodation were also examined in each group. In total, 87 pseudophakic eyes (87 patients) that underwent monofocal intraocular lens (IOL) implantation after uneventful cataract surgery were included. There were 33, 24 and 30 eyes with refractive ATR, WTR and minimum (<0.5 dioptres) astigmatism, respectively. Age, time after surgery, pupil size, corneal and refractive astigmatism, axial length, IOL power, best-corrected visual acuity, corneal multifocality, ocular wavefront aberrations and apparent accommodation without cylindrical correction were compared among the three groups. No significant difference was found in the amount of apparent accommodation between groups. In the ATR group, the amount of apparent accommodation was significantly correlated with pupil size (r=-0.470, p=0.005) and refractive astigmatism (r=0.529, p=0.001). In the WTR group, the amount of apparent accommodation was significantly correlated with coma Zernike term (r=0.409, p=0.047). In the minimum astigmatism group, corneal multifocality was significantly associated with apparent accommodation (r=0.464, p=0.009). There was no significant difference in the average amount of apparent accommodation in pseudophakic eyes with refractive ATR, WTR and minimum astigmatism. However, the factors relevant to apparent accommodation varied depending on the status of postoperative refractive astigmatism. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

  20. The Results of Toric Intraocular Lens Implantation in Patients With Cataract and High Astigmatism After Penetrating Keratoplasty.

    PubMed

    Müftüoğlu, İlkay Klç; Akova, Yonca Aydn; Egrilmez, Sait; Yilmaz, Suzan Guven

    2016-03-01

    To evaluate the results of toric intraocular lens (IOL) implantation in patients with cataract and postpenetrating keratoplasty astigmatism. Seven eyes of 7 patients with cataract and more than 3.5 diopters (D) astigmatism following penetrating keratoplasty were included in this retrospective case series study. All of the eyes underwent phacoemulsification and Acrysof toric IOL (t5-t9) implantation at least 6 months later than the complete suture removal. Corrected visual acuity (CVA), manifest astigmatism, the keratometry measurements, and complications were assessed. The mean preoperative CVA significantly increased (0.7±0.3 [range: 0.3-1.3] logMAR to 0.1±0.04 [range: 0.05-0.15] logMAR; P<0.05) at mean 8.71±4.11 months after the surgery. The mean preoperative corneal astigmatism and the average manifest refractive astigmatism at the last visit were 5.4±0.9 D (range: 4.25-7 D) and 1.6±0.6 D (range: 0.5-2.5 D), respectively. The mean attempted cylinder correction at spectacle plane was 4.3±0.9 D (range: 2.4-4.7 D) whereas the mean cylinder correction was 4.6±0.5 D (range: 3.9-5.9 D), showing a slightly tendency for overcorrection. All eyes (100%) were within 1 D of predicted residual astigmatism. No complication occurred during the follow-up. Toric IOL implantation seems to be an effective, predictable, and safe procedure in patients with cataract formation and high astigmatism after penetrating keratoplasty.

  1. A unique astigmatic nodal property in misaligned Ritchey-Chrétien telescopes with misalignment coma removed.

    PubMed

    Schmid, Tobias; Thompson, Kevin P; Rolland, Jannick P

    2010-03-01

    We present the aberration field response of Ritchey-Chrétien telescopes, with the aperture stop on the primary mirror, to secondary mirror misalignments. More specifically, we derive a general condition for the geometry of the binodal astigmatic aberration field for a telescope that has been aligned to remove field-constant coma. It has been observed that when the coma caused by secondary mirror misalignments is removed the astigmatic field is typically not symmetric around the periphery, but, significantly, it is always effectively zero on-axis. This observation is a manifestation of binodal astigmatism where one of the astigmatic nodes remains near the field center. Here, we show how the condition to remove field-constant coma simultaneously creates a constraint whereby one of the astigmatic nodes must remain effectively on-axis. This result points to why the alignment of a large telescope based on axial imagery is insufficient and demonstrates exactly the geometry of the remaining misalignment aberration field, which dominates the performance of the telescope, providing insights into more complete alignment approaches.

  2. Analysis of anterior corneal astigmatism before cataract surgery using power vector analysis in eyes of Korean patients.

    PubMed

    Oh, Eun-hye; Kim, Hyojin; Lee, Hyun Soo; Hwang, Kyu-yeon; Joo, Choun-Ki

    2015-06-01

    To analyze the pattern of anterior corneal astigmatism before cataract surgery in Korean patients using power vector analysis and to assess the effect of aging on astigmatism. Seoul St. Mary's Hospital, Catholic University of Korea, Seoul, South Korea. Cross-sectional retrospective study. The study evaluated eyes with cataract from May 1, 2009, to July 1, 2013. All eyes received a complete ophthalmologic examination and manual keratometer measurement (OM-4) preoperatively. Power vector J0 and linear regression analyses were used to assess the association between age and anterior corneal astigmatism. The study evaluated 2847 right eyes (2847 patients). The mean age of the patients was 66.64 years ± 12.06 (SD) (range 20 to 100 years); 64.2% of the patients were women. The corneal J0 vector values became progressively negative and trended toward against-the-rule (ATR) astigmatism with increasing age (for men, r = -0.388 and P < .001; for women, r = -0.348 and P < .001). The ATR shift occurred earlier in men than in women. The regression coefficient of J0 values analyzed by age was -0.014 in men and -0.015 in women (both P < .001). Anterior corneal astigmatism in Korean patients with cataract shifted with age from with-the-rule to ATR in both sexes. No author has a financial or proprietary interest in any material or method mentioned. Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  3. Genome-Wide Meta-Analysis of Five Asian Cohorts Identifies PDGFRA as a Susceptibility Locus for Corneal Astigmatism

    PubMed Central

    Fan, Qiao; Zhou, Xin; Khor, Chiea-Chuen; Cheng, Ching-Yu; Goh, Liang-Kee; Sim, Xueling; Tay, Wan-Ting; Li, Yi-Ju; Ong, Rick Twee-Hee; Suo, Chen; Cornes, Belinda; Ikram, Mohammad Kamran; Chia, Kee-Seng; Seielstad, Mark; Liu, Jianjun; Vithana, Eranga; Young, Terri L.; Tai, E.-Shyong

    2011-01-01

    Corneal astigmatism refers to refractive abnormalities and irregularities in the curvature of the cornea, and this interferes with light being accurately focused at a single point in the eye. This ametropic condition is highly prevalent, influences visual acuity, and is a highly heritable trait. There is currently a paucity of research in the genetic etiology of corneal astigmatism. Here we report the results from five genome-wide association studies of corneal astigmatism across three Asian populations, with an initial discovery set of 4,254 Chinese and Malay individuals consisting of 2,249 cases and 2,005 controls. Replication was obtained from three surveys comprising of 2,139 Indians, an additional 929 Chinese children, and an independent 397 Chinese family trios. Variants in PDGFRA on chromosome 4q12 (lead SNP: rs7677751, allelic odds ratio = 1.26 (95% CI: 1.16–1.36), P meta = 7.87×10−9) were identified to be significantly associated with corneal astigmatism, exhibiting consistent effect sizes across all five cohorts. This highlights the potential role of variants in PDGFRA in the genetic etiology of corneal astigmatism across diverse Asian populations. PMID:22144915

  4. Comparison of Moderate- to High-Astigmatism Corrections Using WaveFront-Guided Laser In Situ Keratomileusis and Small-Incision Lenticule Extraction.

    PubMed

    Zhang, Jiamei; Wang, Yan; Chen, Xiaoqin

    2016-04-01

    To evaluate and compare refractive outcomes of moderate- and high-astigmatism correction after wavefront-guided laser in situ keratomileusis (LASIK) and small-incision lenticule extraction (SMILE). This comparative study enrolled a total of 64 eyes that had undergone SMILE (42 eyes) and wavefront-guided LASIK (22 eyes). Preoperative cylindrical diopters were ≤-2.25 D in moderate- and >-2.25 D in high-astigmatism subgroups. The refractive results were analyzed based on the Alpins vector method that included target-induced astigmatism, surgically induced astigmatism, difference vector, correction index, index of success, magnitude of error, angle of error, and flattening index. All subjects completed the 3-month follow-up. No significant differences were found in the target-induced astigmatism, surgically induced astigmatism, and difference vector between SMILE and wavefront-guided LASIK. However, the average angle of error value was -1.00 ± 3.16 after wavefront-guided LASIK and 1.22 ± 3.85 after SMILE with statistical significance (P < 0.05). The absolute angle of error value was statistically correlated with difference vector and index of success after both procedures. In the moderate-astigmatism group, correction index was 1.04 ± 0.15 after wavefront-guided LASIK and 0.88 ± 0.15 after SMILE (P < 0.05). However, in the high-astigmatism group, correction index was 0.87 ± 0.13 after wavefront-guided LASIK and 0.88 ± 0.12 after SMILE (P = 0.889). Both procedures showed preferable outcomes in the correction of moderate and high astigmatism. However, high astigmatism was undercorrected after both procedures. Axial error of astigmatic correction may be one of the potential factors for the undercorrection.

  5. Visual outcomes of topography-guided excimer laser surgery for treatment of patients with irregular astigmatism.

    PubMed

    Ghoreishi, Mohammad; Naderi Beni, Afsaneh; Naderi Beni, Zahra

    2014-01-01

    The aim of this study was to evaluate the efficacy, safety, and predictability of topography-guided treatments to enhance refractive status following other corneal surgical procedures. In a prospective case series study, 28 consecutive eyes of 26 patients with irregular astigmatism after radial keratotomy, corneal transplant, small hyperopic and myopic excimer laser optical zones, and corneal scars were operated. Laser-assisted in situ keratomileusis (LASIK) (n = 8) and photorefractive keratectomy (PRK) (n = 20) were performed using the ALLEGRETTO WAVE excimer laser and topography-guided customized ablation treatment software. Preoperative and postoperative uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), manifest and cycloplegic refraction, and corneal topography with asphericity were analyzed in 12 months follow-up. Uncorrected visual acuity (UCVA) changed from 0.2 ± 0.2 or (20/100 ± 20/100) to 0.51 ± 0.31 or (20/40 ± 20/60) in the LASIK group (P = 0.01) and from 0.34 ± 0.16 or (20/60 ± 20/120) to 0.5 ± 0.23 or (20/40 ± 20/80) in the PRK group (P = 0.01). Refractive cylinder decreased from -3.2 ± 0.84 diopters (D) to -2.06 ± 0.42 D in the LASIK group (P = 0.07) and from -2.25 ± 0.39 D to -1.5 ± 0.23 D in the PRK group (P = 0.008). Best corrected visual acuity did not change significantly in either group. Topography-guided treatment is effective in correcting the irregular astigmatism after refractive surgery. Topography-guided PRK can significantly reduce irregular astigmatism and increase the UCVA and BCVA.

  6. Astigmatic multifocus microscopy enables deep 3D super-resolved imaging

    PubMed Central

    Oudjedi, Laura; Fiche, Jean-Bernard; Abrahamsson, Sara; Mazenq, Laurent; Lecestre, Aurélie; Calmon, Pierre-François; Cerf, Aline; Nöllmann, Marcelo

    2016-01-01

    We have developed a 3D super-resolution microscopy method that enables deep imaging in cells. This technique relies on the effective combination of multifocus microscopy and astigmatic 3D single-molecule localization microscopy. We describe the optical system and the fabrication process of its key element, the multifocus grating. Then, two strategies for localizing emitters with our imaging method are presented and compared with a previously described deep 3D localization algorithm. Finally, we demonstrate the performance of the method by imaging the nuclear envelope of eukaryotic cells reaching a depth of field of ~4µm. PMID:27375935

  7. Astigmatism inducing the degenerate effect in nearly hemispherical cavities: generation of three-dimensional structured light

    NASA Astrophysics Data System (ADS)

    Tung, J. C.; Hsieh, Y. H.; Liang, H. C.; Su, K. W.; Huang, K. F.; Chen, Y. F.

    2017-04-01

    We originally perform an analytical form to explore the influence of the astigmatism on the degenerate effect in nearly hemispherical cavities. The frequency spectrum near hemispherical cavities clearly reveals that not only the difference of cavity lengths between each degeneracies but also frequency gaps have significant difference from non-hemispherical cavities. We further thoroughly demonstrate the laser experiment under the condition of nearly hemispherical cavities to confirm the theoretical exploration that the transverse topology of three-dimensional (3D) structured light in the degenerate cavities is well localized on the Lissajous curves.

  8. Cubic B-spline calibration for 3D super-resolution measurements using astigmatic imaging.

    PubMed

    Proppert, Sven; Wolter, Steve; Holm, Thorge; Klein, Teresa; van de Linde, Sebastian; Sauer, Markus

    2014-05-05

    In recent years three-dimensional (3D) super-resolution fluorescence imaging by single-molecule localization (localization microscopy) has gained considerable interest because of its simple implementation and high optical resolution. Astigmatic and biplane imaging are experimentally simple methods to engineer a 3D-specific point spread function (PSF), but existing evaluation methods have proven problematic in practical application. Here we introduce the use of cubic B-splines to model the relationship of axial position and PSF width in the above mentioned approaches and compare the performance with existing methods. We show that cubic B-splines are the first method that can combine precision, accuracy and simplicity.

  9. LASER MODES AND BEAMS: Invariance of mode transformation by an astigmatic π/2 converter upon the input-beam displacement and tilt

    NASA Astrophysics Data System (ADS)

    Malyutin, A. A.

    2004-10-01

    It is shown theoretically and experimentally that the transformation of modes by an astigmatic π/2 converter is invariant with respect to the input-beam displacement and tilt. The possibility is considered of using this property for manipulating microobjects and simultaneous generation of Laguerre—Gaussian modes of different orders with the help of the same astigmatic π/2 converter.

  10. Long-term outcomes of wedge resection at the limbus for high irregular corneal astigmatism after repaired corneal laceration

    PubMed Central

    Du, Jun; Zheng, Guang-Ying; Wen, Cheng-Lin; Zhang, Xiao-Fang; Zhu, Yu

    2016-01-01

    AIM To evaluate the clinical value of wedge resection at corneal limbus in patients with traumatic corneal scarring and high irregular astigmatism. METHODS Patients with traumatic corneal astigmatism received wedge resection at least 6mo after suture removal from corneal wound. The uncorrected distance visual acuities (UCVA) and best corrected distance visual acuities (BCVA), pre- and post-operation astigmatism, spherical equivalent (SE), safety and complications were evaluated. RESULTS Ten eyes (10 patients) were enrolled in this study. Mean follow-up time after wedge resection was 37.8±15.4mo (range, 20-61mo). The mean UCVA improved from +1.07±0.55 logMAR to +0.43±0.22 logMAR (P=0.000) and the mean BCVA from +0.50±0.30 logMAR to +0.15±0.17 logMAR (P=0.000). The mean astigmatism power measured by retinoscopy was -2.03±2.27 D postoperatively and -2.83±4.52 D preoperatively (P=0.310). The mean SE was -0.74±1.61 D postoperatively and -0.64±1.89 D preoperatively (P=0.601). Two cases developed mild pannus near the sutures. No corneal perforation, infectious keratitis or wound gape occurred. CONCLUSION Corneal-scleral limbal wedge resection with compression suture is a safe, effective treatment for poor patients with high irregular corneal astigmatism after corneal-scleral penetrating injury. Retinoscopy can prove particularly useful for high irregular corneal astigmatism when other measurements are not amenable. PMID:27366685

  11. Arcuate keratotomy on post-keratoplasty astigmatism is unpredictable and frequently needs repeat procedures to increase its success rate.

    PubMed

    Bayramlar, Huseyin; Karadag, Remzi; Cakici, Ozgur; Ozsoy, Isilay

    2016-06-01

    To evaluate the effectiveness and predictability of arcuate keratotomy (AK) for post-keratoplasty astigmatism and to present the complications and rate of repeat procedures. Sixteen eyes from 14 patients were included. Paired 70-80° arc length AKs centred on the steep axis were carried out 0.5 mm within the graft-host junction. The depth of the AKs was set at approximately 80-90% of the depth of the cornea, based on a topographic pachymeter at the incision location. The outcome measures included preoperative and postoperative topographic astigmatism, uncorrected and corrected visual acuity, surgical complications and repeat procedures. In 12 of the 16 eyes (75%), at least one additional surgical procedure was required to obtain the desired result: suturing for overcorrection or wound gape in six eyes (38%), lengthening of the incisions for undercorrection in four eyes (25%) and additional AKs for marked astigmatic axis displacement in three eyes (19%). The mean preoperative astigmatism was 10.45±3.82 dioptres (D); the postoperative astigmatism at the last visit was 2.99±1.14 D (in a mean follow-up of 17.6±5.55 months). The efficacy index was 0.83 and the safety index was 1.68. In treatment of post-keratoplasty astigmatism, AK does not have a good predictability. Additional procedures such as lengthening of the AK incisions for undercorrection or using compression sutures for overcorrection with significantly gaping wounds are frequently required to improve the final outcome. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

  12. Apparatus for and method of correcting for astigmatism in a light beam reflected off of a light reflecting surface

    DOEpatents

    Sawicki, R.H.; Sweatt, W.

    1985-11-21

    A technique for adjustably correcting for astigmatism in a light beam is disclosed herein. This technique defines a flat, rectangular light reflecting surface having opposite reinforced side edges and which is resiliently bendable, to a limited extent, into different concave and/or convex cylindrical curvatures about a particular axis and provides for adjustably bending the light reflecting surface into one of different curvatures depending upon the astigmatism to be corrected and for fixedly maintaining the curvature selected. In the embodiment disclosed, the light reflecting surface is adjustably bendable into the selected cylindrical curvature by application of a particular bending moment to the reinforced side edges of the light reflecting surface.

  13. Refractive lenticule extraction (ReLEx) through a small incision (SMILE) for correction of myopia and myopic astigmatism: current perspectives

    PubMed Central

    Ağca, Alper; Demirok, Ahmet; Yıldırım, Yusuf; Demircan, Ali; Yaşa, Dilek; Yeşilkaya, Ceren; Perente, İrfan; Taşkapılı, Muhittin

    2016-01-01

    Small-incision lenticule extraction (SMILE) is an alternative to laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) for the correction of myopia and myopic astigmatism. SMILE can be performed for the treatment of myopia ≤−12 D and astigmatism ≤5 D. The technology is currently only available in the VisuMax femtosecond laser platform. It offers several advantages over LASIK and PRK; however, hyperopia treatment, topography-guided treatment, and cyclotorsion control are not available in the current platform. The working principles, potential advantages, and disadvantages are discussed in this review. PMID:27757010

  14. Risk factors for astigmatism in preschool children: the multi-ethnic pediatric eye disease and Baltimore pediatric eye disease studies.

    PubMed

    McKean-Cowdin, Roberta; Varma, Rohit; Cotter, Susan A; Tarczy-Hornoch, Kristina; Borchert, Mark S; Lin, Jesse H; Wen, Ge; Azen, Stanley P; Torres, Mina; Tielsch, James M; Friedman, David S; Repka, Michael X; Katz, Joanne; Ibironke, Josephine; Giordano, Lydia

    2011-10-01

    To evaluate risk factors for astigmatism in a population-based sample of preschool children. Population-based cross-sectional study. Population-based samples of 9970 children ages 6 to 72 months from Los Angeles County, California, and Baltimore, Maryland. A cross-sectional study of children participating in the Multiethnic Pediatric Eye Disease Study and the Baltimore Eye Disease Study was completed. Data were obtained by clinical examination or by in-person interview. Odds ratios and 95% confidence intervals (CI) were calculated to evaluate potential associations between clinical, behavioral, or demographic factors and astigmatism. Odds ratios (ORs) for various risk factors associated with astigmatism. Participants with myopia (≤-1.0 diopters) were 4.6 times as likely to have astigmatism (95% CI, 3.56-5.96) than those without refractive error, whereas participants with hyperopia (≥+2.00 diopters) were 1.6 times as likely (95% CI, 1.39-1.94). Children 6 to <12 months of age were approximately 3 times as likely to have astigmatism than children 5 to 6 years of age (95% CI, 2.28-3.73). Both Hispanic (OR, 2.38) and African-American (OR, 1.47) children were as likely to have astigmatism than non-Hispanic white children. Furthermore, children whose mothers smoked during pregnancy were 1.46 times (95% CI, 1.14-1.87) as likely to have astigmatism than children whose mothers did not smoke. In addition to infancy, Hispanic and African-American race/ethnicity and correctable/modifiable risk factors such as myopia, hyperopia, and maternal smoking during pregnancy are associated with a higher risk of having astigmatism. Although the prevalence of smoking during pregnancy is typically low, this association may suggest etiologic pathways for future investigation. The authors have no proprietary or commercial interest in any of the materials discussed in this article. Copyright © 2011 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.

  15. Optimization of nonimaging focusing heliostat in dynamic correction of astigmatism for a wide range of incident angles.

    PubMed

    Chong, Kok-Keong

    2010-05-15

    To overcome astigmatism has always been a great challenge in designing a heliostat capable of focusing the sunlight on a small receiver throughout the year. In this Letter, a nonimaging focusing heliostat with a dynamic adjustment of facet mirrors in a group manner has been analyzed for optimizing the astigmatic correction in a wide range of incident angles. This what is to the author's knowledge a new heliostat is not only designed to serve the purpose of concentrating sunlight to several hundreds of suns, but also to significantly reduce the variation of the solar flux distribution with the incident angle.

  16. Note: Measurement of synchrotron radiation phase-space beam properties to verify astigmatism compensation in Fresnel zone plate focusing optics

    NASA Astrophysics Data System (ADS)

    Kagoshima, Yasushi; Miyagawa, Takamasa; Kagawa, Saki; Takeda, Shingo; Takano, Hidekazu

    2017-08-01

    The intensity distribution in phase space of an X-ray synchrotron radiation beamline was measured using a pinhole camera method, in order to verify astigmatism compensation by a Fresnel zone plate focusing optical system. The beamline is equipped with a silicon double crystal monochromator. The beam size and divergence at an arbitrary distance were estimated. It was found that the virtual source point was largely different between the vertical and horizontal directions, which is probably caused by thermal distortion of the monochromator crystal. The result is consistent with our astigmatism compensation by inclining a Fresnel zone plate.

  17. Mode-coupling enhancement by pump astigmatism correction in a Ti:Sapphire femtosecond laser.

    PubMed

    Ramírez-Guerra, Catalina; Moreno-Larios, José Agustín; Rosete-Aguilar, Martha; Garduño-Mejía, Jesús

    2016-12-01

    To pump a solid-state femtosecond laser cavity, a beam from a CW laser is focused by a single lens into the laser crystal. To increase the output power of the laser, the overlap of the laser mode with the pump mode should be maximized. This is particularly important in the so-called mode coupling and the Kerr-lens mode locking (KLM) operation, where the change in beam waist at the position of the gain medium is exploited to enhance the mode overlap with the pump laser in the crystal. In this paper, the astigmatism in the pump beam is reduced by tilting the pump lens. A Gaussian beam is propagated through the complete focusing system-pump lens, tilted spherical mirror, and crystal cut at Brewster's angle-to show the astigmatism inside the crystal as a function of the tilt of the pump lens. A genetic algorithm is presented to optimize the mode coupling between the pump and laser beam inside the crystal by tilting the pump lens. Experimental results are presented to verify the design, showing an increase in the output power of the laser cavity of about 20%.

  18. Characterization of a tunable astigmatic fluidic lens with adaptive optics correction for compact phoropter application

    NASA Astrophysics Data System (ADS)

    Fuh, Yiin-Kuen; Huang, Chieh-Tse

    2014-07-01

    Fluidically controlled lenses which adaptively correct prescribed refractive error without mechanically moving parts are extensively applied in the ophthalmic applications. Capable of variable-focusing properties, however, the associated aberrations due to curvature change and refractive index mismatch can inherently degrade image quality severely. Here we present the experimental study of the aberrations in tunable astigmatic lens and use of adaptive optics to compensate for the wavefront errors. Characterization of the optical properties of the individual lenses is carried out by Shack-Hartmann measurements. An adaptive optics (AO) based scheme is demonstrated for three injected fluidic volumes, resulting in a substantial reduction of the wavefront errors from -0.12, -0.25, -0.32 to 0.01, -0.01, -0.20 μm, respectively, corresponding to the optical power tenability of 0.83 to 1.84 D. Furthermore, an integrated optical phoroptor consisting of adjustable astigmatic lenses and AO correction is demonstrated such that an induced refraction error of -1 D cylinder at 180° of a model eye vision is experimentally corrected.

  19. Independent control of beam astigmatism and ellipticity using a SLM for fs-laser waveguide writing.

    PubMed

    Ruiz de la Cruz, A; Ferrer, A; Gawelda, W; Puerto, D; Sosa, M Galván; Siegel, J; Solis, J

    2009-11-09

    We have used a low repetition rate (1 kHz), femtosecond laser amplifier in combination with a spatial light modulator (SLM) to write optical waveguides with controllable cross-section inside a phosphate glass sample. The SLM is used to induce a controllable amount of astigmatism in the beam wavefront while the beam ellipticity is controlled through the propagation distance from the SLM to the focusing optics of the writing set-up. The beam astigmatism leads to the formation of two separate disk-shaped foci lying in orthogonal planes. Additionally, the ellipticity has the effect of enabling control over the relative peak irradiances of the two foci, making it possible to bring the peak irradiance of one of them below the material transformation threshold. This allows producing a single waveguide with controllable cross-section. Numerical simulations of the irradiance distribution at the focal region under different beam shaping conditions are compared to in situ obtained experimental plasma emission images and structures produced inside the glass, leading to a very satisfactory agreement. Finally, guiding structures with controllable cross-section are successfully produced in the phosphate glass using this approach.

  20. [Abnormal head position caused by incorrect prescription for astigmatism: case report].

    PubMed

    Castro, Flávia Augusta Attié de; Simão, Maria Lúcia Habib; Abbud, Christine Mae Morello; Foschini, Rosália Maria Simões Antunes; Bicas, Harley Edison Amaral

    2005-01-01

    Abnormal head position is a compensatory condition which improves patients' vision. It can be caused by ophthalmological problems such as oculomotor imbalances (strabismus, nystagmus) and high astigmatism. However, it results in esthetic impairment, orthopedic trouble and facial asymmetries. We describe a case of a girl, JL, 8 years, with abnormal head position tilted to the left since the last glasses were prescribed. The correction used by the patient was: right eye = +2.00 sph diopter -5.5 cyl 180 degrees and left eye = +2.25 sph diopter -5.75 cyl 180 degrees. In tilted position, the correct visual acuity was: right eye 6/12 and left eye 6/9. No deviations were noted by the cover test and the remaining ophthalmological examination was completely normal. Retinoscopy under cycloplegia and subjective test showed right eye = +3.50 sph diopter -6.00 cyl 10 degrees; and left eye = +3.50 sph diopter -6.00 cyl 170 degrees, with visual acuity 6/6 in both eyes. With adequate prescription, the head position was normalized. Wrong cylindrical positions for correction of high astigmatism may cause abnormal head position. Retinoscopy under cycloplegia and subjective test are essential for precise diagnoses and prescriptions.

  1. Laser-assisted in situ keratomileusis in high mixed astigmatism with optimized, fast-repetition and cyclotorsion control excimer laser.

    PubMed

    Alio, Jorge L; Pachkoria, Ketevan; El Aswad, Amr; Plaza-Puche, Ana Belen

    2013-05-01

    To evaluate the visual refractive and aberrometric outcomes of laser-assisted in situ keratomileusis (LASIK) surgery for the correction of high mixed astigmatism using a new-generation excimer laser and optimized aspherical profiles. Retrospective interventional case series. Fifty-two eyes of 36 patients (21-53 years) with primary mixed astigmatism over 3.0 diopters (D) were included. All cases underwent LASIK surgery using the sixth-generation excimer laser Amaris with cyclotorsion control and a femtosecond platform for flap creation. Visual, refractive, corneal topographic, and aberrometric outcomes were evaluated during a 3-month follow-up. Refractive astigmatic changes were analyzed by Alpins method. A significant reduction of refractive sphere and cylinder was observed 3 months postoperatively (P = .001), with an associated improvement of uncorrected distance visual acuity (P = .001). Best-corrected distance visual acuity (CDVA) remained unchanged in 31 eyes (59.6%), while 3 eyes (5.76%) lost 2 lines of CDVA. Fourteen eyes (26.9%) had spherical equivalent (SE) within ±0.5 D of emmetropia and 34 (65.3%) had SE within ±1.0 D of emmetropia. No significant difference was observed when comparing surgically induced and target astigmatism. A significant induction of higher-order aberration attributable to increase of spherical aberration was found (P = .003). Seven eyes (13.4%) required retreatment. LASIK for primary high mixed astigmatism using optimized aspherical profiles and a fast-repetition-rate excimer laser with cyclotorsion control is a safe, effective, and predictable procedure. Induction of higher-order aberrations is still present in the correction of the refraction error of the magnitude included in this study. Copyright © 2013 Elsevier Inc. All rights reserved.

  2. Higher-order aberrations and best-corrected visual acuity in Native American children with a high prevalence of astigmatism

    PubMed Central

    Miller, Joseph M.; Harvey, Erin M.; Schwiegerling, Jim

    2016-01-01

    Purpose To determine whether higher-order aberrations (HOAs) in children from a highly astigmatic population differ from population norms and whether HOAs are associated with astigmatism and reduced best-corrected visual acuity. Methods Subjects were 218 Tohono O’odham Native American children 5–9 years of age. Noncycloplegic HOA measurements were obtained with a handheld Shack-Hartmann sensor (SHS). Signed (z06s to z14s) and unsigned (z06u to z14u) wavefront aberration Zernike coefficients Z(3,−3) to Z(4,4) were rescaled for a 4 mm diameter pupil and compared to adult population norms. Cycloplegic refraction and best-corrected logMAR letter visual acuity (BCVA) were also measured. Regression analyses assessed the contribution of astigmatism (J0) and HOAs to BCVA. Results The mean root-mean-square (RMS) HOA of 0.191 ± 0.072 μm was significantly greater than population norms (0.100 ± 0.044 μm. All unsigned HOA coefficients (z06u to z14u) and all signed coefficients except z09s, z10s, and z11s were significantly larger than population norms. Decreased BCVA was associated with astigmatism (J0) and spherical aberration (z12u) but not RMS coma, with the effect of J0 about 4 times as great as z12u. Conclusions Tohono O’odham children show elevated HOAs compared to population norms. Astigmatism and unsigned spherical aberration are associated with decreased acuity, but the effects of spherical aberration are minimal and not clinically significant. PMID:26239206

  3. Validity of autorefractor based screening method for irregular astigmatism compared to the corneal topography- a cross sectional study.

    PubMed

    Galindo-Ferreiro, Alicia; De Miguel-Gutierrez, Julita; González-Sagrado, Manuel; Galvez-Ruiz, Alberto; Khandekar, Rajiv; Schellini, Silvana; Galindo-Alonso, Julio

    2017-01-01

    To present a method of screening for irregular astigmatism with an autorefractor and its determinants compared to corneal topography. This cross-sectional validity study was conducted in 2013 at an eye hospital in Spain. A tabletop autorefractor (test 1) was used to measure the refractive status of the anterior surface of the cornea at two corneal meridians of each eye. Then corneal topography (test 2) and Bogan's classification was used to group eyes into those with regular or no astigmatism (GRI) and irregular astigmatism (GRII). Test 1 provided a single absolute value for the greatest cylinder difference (Vr). The receiver operating characteristic (ROC) were plotted for the Vr values measured by test 1 for GRI and GRII eyes. On the basis a Vr value of 1.25 D as cut off, sensitivity, specificity were also calculated. The study sample was comprised of 260 eyes (135 patients). The prevalence of irregular astigmatism was 42% [95% confidence interval (CI): 36, 48]. Based on test 2, there were 151 eyes in GRI and 109 eyes in GRII. The median Vr was 0.75 D (25% quartile, 0.5 D) for GRI and 1.75 D (25% quartile, 1.25 D) for GRII. The area under curve was 0.171 for GRI and 0.83 for GRII. The sensitivity of test I was 78.1% and the specificity was 76.1%. A conventional autorefractor can be effective as a first level screening method to detect irregular corneal astigmatism in places where corneal topography facilities are not available.

  4. The Prevalence of Astigmatism and its Determinants in a Rural Population of Iran: The “Nooravaran Salamat” Mobile Eye Clinic Experience

    PubMed Central

    Hashemi, Hassan; Rezvan, Farhad; Yekta, Abbas Ali; Hashemi, Maryam; Norouzirad, Reza; Khabazkhoob, Mehdi

    2014-01-01

    Purpose: The prevalence of astigmatism, and the astigmatic axis, and their determinants were evaluated in a rural population of Iran. Materials and Methods: In a cross-sectional study conducted from May to August 2011, 13 villages in the vicinity of the city of Khaf in northeast Iran were investigated in this study. All the examinations including visual acuity, refraction, slit-lamp biomicroscopy and fundoscopy were performed in a Mobile Eye Clinic. Written informed consent was obtained from all participants. Only phakic eye that could be reliably refracted without a previous history of ocular surgery were included. Results: Out of 2635 participants who were screened, 2124 were analysed for this study of whom 52% were female. The prevalence of astigmatism was 32.2% (95% confidence intervals (CI): 30.2-34.2). Astigmatism significantly increased from 14.3% in the under 15-year-old age group to 67.2% in the age group of over 65-years old (P < 0.001). The prevalence of With-The-Rule (WTR), Against-The-Rule (ATR), and oblique astigmatism was 11.7%, 18.1%, and 2.4 %, respectively. ATR significantly increased with age (P < 0.001). The mean corneal astigmatism was 0.73 D which linearly increased with age (P < 0.001). Conclusion: Attention must be paid to astigmatism in rural areas due to the high prevalence. Further studies are suggested to discover the role of the environmental and genetic factors. It seems that environmental and occupational factors in the villages cause a significant increase in the prevalence of astigmatism with age. A high percentage of participants had ATR astigmatism, which was more common at older ages. PMID:24791111

  5. Image digitalization and processing of contact lens fitting to astigmatic eyes

    NASA Astrophysics Data System (ADS)

    Costa, Manuel F. M.

    1998-01-01

    The use of standard CCD cameras and image digitalization and processing on medical diagnosis are more and more frequent. The correction of human eye's refraction problems by the use of contact lenses is generalized. In spite its advantages in terms of users comfort, special care must be taken on its prescription and adaptation. Astigmatic eyes often place the highest problems. A careful assessment of the quality of the lens to cornea adaptation must to be performed. The basic and more traditional way to check the contact lens' fitting is to perform a fluorescein test. We intend to make the process more convenient for both patient and optometrist. The fluorescence images are acquired by a CCD camera and then digitized and processed in order to produce a semi- automated process.

  6. Digital in-line holography for the characterization of flowing particles in astigmatic optical systems

    NASA Astrophysics Data System (ADS)

    Sentis, Matthias P. L.; Bruel, Laurent; Charton, Sophie; Onofri, Fabrice R. A.; Lamadie, Fabrice

    2017-01-01

    An extended Generalized Fresnel Transform (GFT) is proposed to account for the astigmatism introduced by optical elements described, in the paraxial approximation, with a ray transfer matrix analysis. Generalized impulse response and generalized Fresnel transfer function propagators as well as sampling conditions are derived to properly implement this transformation. As a test case, the near-field diffraction patterns and in-line holograms produced by droplets flowing in a tube with cylindrical interfaces have been simulated. A best fitting approach is introduced to retrieve, from the propagated holograms, the 3D position and size of the droplets. Several hologram focusing indicators based on the analysis of droplets focus region are also proposed to further improve the estimation of the droplets position along the optical axis. Numerical simulations and experimental results confirm the applicability and accuracy of the proposed methods.

  7. [Orthokeratology for the high myopia and high astigmatism is worth watching].

    PubMed

    Xie, Peiying

    2015-01-01

    The prevalence of high myopia in teenagers is rising. Due to both genetic factors and environmental factors, most of myopia occurs in early age with rapid progress, and the prevention and control are very difficult. Orthokeratology is considered as one of the most effective ways of controlling myopia for children. It is proved effective through many years of clinical studies not only for low to moderate myopia, but also for high myopia with astigmatism. However, professional knowledge is lacking domestically. This paper introduces the local and overseas research results in recent years, and discusses the necessity and feasibility of high diopter orthokeratology correction, implementation methods and requirements, and safety and effectiveness evaluation standards for reference.

  8. Corneal graft curvature change after relaxing incisions for post-penetrating keratoplasty astigmatism.

    PubMed

    Feizi, Sepehr; Javadi, Mohammad A

    2012-09-01

    To evaluate change in graft steepness after graft refractive surgery (GRS) consisting of relaxing incisions with or without counterquadrant compression sutures and discover the existing influential factors. In this retrospective study, 78 eyes of 76 patients who had received penetrating keratoplasty for keratoconus underwent GRS because of high post-penetrating keratoplasty astigmatism. Any shift in graft curvature was calculated using the keratometric coupling ratio (CR; the ratio of flattening of the incised meridian to steepening of the opposite meridian). Multiple regression analysis was used to investigate the possible effect of age, graft curvature, number of incisions, use of compression sutures, achieved vector astigmatic correction, and total arc length on CR. Mean patient age was 30.1 ± 10.3 years and mean follow-up period after GRS was 40.1 ± 29.0 months. There was a significant increase in average keratometry from 44.79 ± 2.08 diopters (D) preoperatively to 45.65 ± 1.86 D postoperatively (P < 0.001). Mean keratometric CR was 0.62 ± 1.09. Keratometric CR was significantly associated with patient age (R = 0.53, P = 0.04) and preoperative average keratometry (R = 0.61, P = 0.02). However, keratometric CR failed to show any significant correlation with other variables. A significant increase in graft steepening occurred after GRS, averaging 0.86 D. When both GRS and cataract extraction or phakic intraocular lens implantation are indicated, a staged approach (first GRS followed by phacoemulsification, for example) is advocated to calculate intraocular lens power with accuracy.

  9. Toric Intraocular Lenses in the Correction of Astigmatism During Cataract Surgery: A Systematic Review and Meta-analysis.

    PubMed

    Kessel, Line; Andresen, Jens; Tendal, Britta; Erngaard, Ditte; Flesner, Per; Hjortdal, Jesper

    2016-02-01

    We performed a systematic review and meta-analysis to evaluate the benefit and harms associated with implantation of toric intraocular lenses (IOLs) during cataract surgery. Outcomes were postoperative uncorrected distance visual acuity (UCDVA) and distance spectacle independence. Harms were evaluated as surgical complications and residual astigmatism. Postoperative astigmatism is an important cause of suboptimal UCDVA and need for distance spectacles. Toric IOLs may correct for preexisting corneal astigmatism at the time of surgery. We performed a systematic literature search in the Embase, PubMed, and CENTRAL databases within the Cochrane Library. We included randomized clinical trials (RCTs) if they compared toric with non-toric IOL implantation (± relaxing incision) in patients with regular corneal astigmatism and age-related cataracts. We assessed the risk of bias using the Cochrane Risk of Bias tool. We assessed the quality of evidence across studies using the GRADE profiler software (available at: www.gradeworkinggroup.org). We included 13 RCTs with 707 eyes randomized to toric IOLs and 706 eyes randomized to non-toric IOLs; 225 eyes had a relaxing incision. We found high-quality evidence that UCDVA was better in the toric IOL group (logarithm of the minimum angle of resolution [logMAR] mean difference, -0.07; 95% confidence interval [CI], -0.10 to -0.04) and provided greater spectacle independence (risk ratio [RR], 0.51; 95% CI, 0.36-0.71) and moderate quality evidence that toric IOL implantation was not associated with an increased risk of complications (RR, 1.73; 95% CI, 0.60-5.04). Residual astigmatism was lower in the toric IOL group than in the non-toric IOL plus relaxing incision group (mean difference, 0.37 diopter [D]; 95% CI, -0.55 to -0.19). We found that toric IOLs provided better UCDVA, greater spectacle independence, and lower amounts of residual astigmatism than non-toric IOLs even when relaxing incisions were used. Copyright © 2016

  10. The use of WaveLight® Contoura to create a uniform cornea: the LYRA Protocol. Part 1: the effect of higher-order corneal aberrations on refractive astigmatism

    PubMed Central

    Motwani, Manoj

    2017-01-01

    Purpose To demonstrate how higher-order corneal aberrations can cancel out, modify, or induce lower-order corneal astigmatism. Patients and methods Six representative eyes are presented that show different scenarios in which higher-order aberrations interacting with corneal astigmatism can affect the manifest refraction. WaveLight® Contoura ablation maps showing the higher-order aberrations are shown, as are results of correction with full measured correction using the LYRA (Layer Yolked Reduction of Astigmatism) Protocol. Results Higher-order corneal aberrations such as trefoil, quadrafoil, and coma can create ovalization of the central cornea, which can interact with the ovalization caused by lower-order astigmatism to either induce, cancel out, or modify the manifest refraction. Contoura processing successfully determines the linkage of these interactions resulting in full astigmatism removal. Purely lenticular astigmatism appears to be rare, but a case is also demonstrated. The author theorizes that all aberrations require cerebral compensatory processing and can be removed, supported by the facts that full removal of aberrations and its linkage with lower-order astigmatism with the LYRA Protocol has not resulted in worse or unacceptable vision for any patients. Conclusion Higher-order aberrations interacting with lower-order astigmatism is the main reason for the differences between manifest refraction and Contoura measured astigmatism, and the linkage between these interactions can be successfully treated using Contoura and the LYRA Protocol. Lenticular astigmatism is relatively rare. PMID:28553069

  11. Evaluation of the orientation of the steepest meridian of regular astigmatism among highly myopic Egyptian patients seeking non-ablative surgical correction of the refractive error

    PubMed Central

    Refai, Tamer Adel

    2015-01-01

    Introduction: LASIK surgery is currently the preferred procedure to correct low to moderate myopia. The aim of this study was to determine the orientation of the steepest meridian of regular astigmatism in order to determine the relative incidence of vertical, horizontal, and oblique regular astigmatism among highly myopic Egyptian patients seeking non-ablative surgical correction of the refractive error. Methods: One hundred and one eyes of 68 highly myopic patients who were seeking refractive surgery were included in this consecutive case series study. The refractive errors were measured using an autorefractometer and confirmed by trial. We measured the uncorrected and best corrected visual acuity in Snellen lines. Keratometry, central corneal thickness, and anterior chamber depth also were measured. The cylinder power in diopters and the axis in degrees were reported. Astigmatism was graded as with the rule (i.e., vertical meridian steeper), against the rule (i.e., horizontal meridian steeper), and oblique astigmatism. The number and the percentage of eyes with the rule, against the rule, and oblique astigmatism were calculated, and the chi-squared test was performed to analyze the data. Results: The spherical refractive error ranged from −6.5 to −24.5 diopters (−13.45 ± 4.60). The cylinder power (Cyl) ranged from −0.25 to −7.5 diopters (−2.23 ± 1.28). The uncorrected visual acuity (UCVA) in Snellen lines ranged from 0.01 – 0.1 (0.03 ± 0.02). The mean for best corrected visual acuity (BCVA) in Snellen lines was 0.40 (± 0.23). The steepest meridian was vertical (i.e., with-the-rule astigmatism) in 44 eyes (43.56%), horizontal (i.e., against-the-rule astigmatism) in 27 eyes (26.73%), and oblique (i.e., oblique astigmatism) in 30 eyes (29.70%). Conclusions: The incidence of with-the-rule astigmatism in patients with high myopia was found to be much lower than in previous studies for non-myopic patients, with a higher incidence for against

  12. LASER MODES AND BEAMS: Tunable astigmatic π/2 converter of laser modes with a fixed distance between input and output planes

    NASA Astrophysics Data System (ADS)

    Malyutin, A. A.

    2006-01-01

    The scheme of a tunable astigmatic π/2 mode converter is proposed in which the distance between input and output planes is fixed. The converter is tuned only by rotating the cylindrical components of optical quadrupoles used in the converter around its optical axis. The Gouy phase difference in the orthogonal planes of the astigmatic π/2 converter required for mode conversion was achieved for the first time by using the scaled fractional Fourier transforms of the appropriate orders.

  13. Dependence of astigmatism, far-field pattern, and spectral envelope width on active layer thickness of gain guided lasers with narrow stripe geometry

    SciTech Connect

    Mamine, T.

    1984-06-15

    The effects of active layer thickness on the astigmatism, the angle of far-field pattern width parallel to the junction, and the spectral envelope width of a gain guided laser with a narrow stripe geometry have been investigated analytically and experimentally. It is concluded that a large level of astigmatism, a narrow far-field pattern width, and a rapid convergence of the spectral envelope width are inherent to the gain guided lasers with thin active layers.

  14. Combined intrastromal astigmatic keratotomy and laser in situ keratomileusis flap followed by photoablation to correct post-penetrating keratoplasty ametropia and high astigmatism: One-year follow-up.

    PubMed

    Shalash, Riad B; Elshazly, Malak I; Salama, Marwa M

    2015-10-01

    To evaluate a new technique combining intrastromal astigmatic keratotomy (AK) with a laser in situ keratomileusis (LASIK) flap followed by excimer laser photoablation to correct post-penetrating keratoplasty (PKP) high astigmatism and ametropia. Kasr El Aini Hospital, Cairo University, Cairo, Egypt. Prospective interventional uncontrolled case series. Patients with post-PKP high astigmatism and ametropia had paired intrastromal AK with LASIK flap using the M2 microkeratome followed 2 to 3 months later by excimer laser photoablation. The main outcome measures were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), mean refractive spherical equivalent (SE), and mean cylinder after each step and at the 1-year follow-up. The study comprised 20 eyes (20 patients). All parameters were significantly improved in all patients by the last follow-up visit. The mean UDVA improved from 1.07 logMAR ± 0.2 (SD) preoperatively to 0.23 ± 0.18 logMAR (P < .001), the mean CDVA improved from 0.79 ± 0.18 logMAR to 0.12 ± 0.12 logMAR (P < .001), the mean refractive SE improved from -5.04 ± 2.62 diopters (D) to -1.47 ± 1.32 D (P = .001), and the mean cylinder reduced from -5.39 ± 0.98 D to -1.05 ± 0.71 D (P < .001). The mean correction index was 0.84 ± 0.10, and the mean flattening index was 0.83 ± 0.10. Thirty-five percent of cases developed microperforations, and 15% developed epithelial ingrowth. This combined approach allowed for the correction of high astigmatism and ametropia following PKP; however, epithelial ingrowth requiring intervention is a complication to be considered. No author has a financial or proprietary interest in any material or method mentioned. Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  15. Apparatus for and method of correcting for astigmatism in a light beam reflected off of a light reflecting surface

    DOEpatents

    Sawicki, Richard H.; Sweatt, William

    1987-01-01

    A technique for adjustably correcting for astigmatism in a light beam is disclosed herein. This technique utilizes first means which defines a flat, rectangular light reflecting surface having opposite reinforced side edges and which is resiliently bendable, to a limited extent, into different concave and/or convex cylindrical curvatures about a particular axis and second means acting on the first means for adjustably bending the light reflecting surface into a particular selected one of the different curvatures depending upon the astigmatism to be corrected for and for fixedly maintaining the curvature selected. In the embodiment disclosed, the light reflecting surface is adjustably bendable into the selected cylindrical curvature by application of a particular bending moment to the reinforced side edges of the light reflecting surface.

  16. Reflection and refraction of narrow Gaussian beams with general astigmatism at tilted optical surfaces: a derivation oriented toward lens design.

    PubMed

    Greco, Vincenzo; Giusfredi, Giovanni

    2007-02-01

    The formulas for the reflection and refraction of a narrow Gaussian beam with general astigmatism at a tilted optical surface are derived by ray-tracing techniques. The propagation direction of the reflected and refracted beams is computed by tracing the central ray of the incident beam, and the characteristic parameters of the respective wavefronts are worked out by applying the formulas developed for the generalized ray tracing. Moreover, the Gaussian form of the reflected and refracted amplitude distributions along the transverse coordinates is determined by requiring the matching of the incident, reflected, and refracted light spots on the optical surface. No limiting assumptions are made regarding the form of the optical interface or the orientation of the incident astigmatic wavefront. In the end, to illustrate a simple application of these formulas, the reflection of a Gaussian beam at a conicoid is considered, and a simple property of the conicoidal mirrors is reported.

  17. Management of moderate and severe corneal astigmatism with AcrySof® toric intraocular lens implantation – Our experience

    PubMed Central

    Farooqui, Javed Hussain; Koul, Archana; Dutta, Ranjan; Shroff, Noshir Minoo

    2015-01-01

    Purpose Visual performance following toric intraocular lens implantation for cataract with moderate and severe astigmatism. Setting Cataract services, Shroff Eye Centre, New Delhi, India. Design Case series. Method This prospective study included 64 eyes of 40 patients with more than 1.50 dioptre (D) of pre-existing corneal astigmatism undergoing phacoemulsification with implantation of the AcrySof® toric IntraOcular Lens (IOL). The unaided visual acuity (UCVA), best corrected visual acuity (BCVA), residual refractive sphere and refractive cylinders were evaluated. Toric IOL axis and alignment error was measured by slit lamp method and Adobe Photoshop (version 7) method. Patient satisfaction was evaluated using a satisfaction questionnaire at 3 months. Results The mean residual refractive astigmatism was 0.57 D at the final follow-up of 3 months. Mean alignment error was 3.44 degrees (SD = 2.60) by slit lamp method and 3.88 degrees (SD = 2.86) by Photoshop method. Forty-six (71.9%) eyes showed misalignment of 5 degrees or less, and 60 (93.8%) eyes showed misalignment of 10 degrees or less. The mean log MAR UCVA at 1st post-op day was 0.172 (SD = 0.02), on 7th post-op day was 0.138 (SD = 0.11), and on 30th post-op day was 0.081 (SD = 0.11). The mean log MAR BCVA at three months was −0.04 (SD = 0.76). Conclusion We believe that implantation of AcrySof® toric IOL is an effective, safe and predictable method to correct high amounts of corneal astigmatism during cataract surgery. PMID:26586976

  18. Correction of astigmatism after cataract surgery using the light adjustable lens: a 1-year follow-up pilot study.

    PubMed

    Lichtinger, Alejandro; Sandstedt, Christopher A; Schwartz, Daniel M; Chayet, Arturo S

    2011-09-01

    The management of preoperative and residual astigmatism is critical to obtain optimized uncorrected visual acuity. The aim of this study was to determine whether residual astigmatism could be precisely corrected postoperatively using the Light Adjustable Lens (LAL, Calhoun Vision Inc) and to determine the stability of the adjusted refraction. Ten eyes of 10 patients with cataract and corneal astigmatism between 1.00 and 2.00 diopters (D) were included. After standard phacoemulsification and implantation of the LAL, adjustment and lock-in procedures were completed. Before adjustment and 2 weeks, 6 months, and 1 year after lock-in, a full ophthalmic examination including uncorrected distance acuity (UDVA) and corrected distance visual acuity (CDVA), autorefraction, and manifest refraction was performed. All surgeries, adjustments, and lock-in procedures were performed with no complications. All eyes achieved ±0.50 D of the targeted cylindrical adjustment. Mean spherical equivalent refraction was 0.03±0.84 D before adjustment and -0.06±0.25 D at final follow-up. The cylinder axis remained the same in 60% of eyes and all eyes were stable within 10° rotation at 12-month follow-up. Seven of 10 eyes achieved UDVA of 20/25 or better whereas all eyes achieved UDVA of 20/32 or better. Corrected distance visual acuity remained stable in all eyes. In this pilot study, the LAL proved to be an efficient, predictable, and stable method of managing astigmatism in cataract patients. Copyright 2011, SLACK Incorporated.

  19. Management of moderate and severe corneal astigmatism with AcrySof® toric intraocular lens implantation - Our experience.

    PubMed

    Farooqui, Javed Hussain; Koul, Archana; Dutta, Ranjan; Shroff, Noshir Minoo

    2015-01-01

    Visual performance following toric intraocular lens implantation for cataract with moderate and severe astigmatism. Cataract services, Shroff Eye Centre, New Delhi, India. Case series. This prospective study included 64 eyes of 40 patients with more than 1.50 dioptre (D) of pre-existing corneal astigmatism undergoing phacoemulsification with implantation of the AcrySof® toric IntraOcular Lens (IOL). The unaided visual acuity (UCVA), best corrected visual acuity (BCVA), residual refractive sphere and refractive cylinders were evaluated. Toric IOL axis and alignment error was measured by slit lamp method and Adobe Photoshop (version 7) method. Patient satisfaction was evaluated using a satisfaction questionnaire at 3 months. The mean residual refractive astigmatism was 0.57 D at the final follow-up of 3 months. Mean alignment error was 3.44 degrees (SD = 2.60) by slit lamp method and 3.88 degrees (SD = 2.86) by Photoshop method. Forty-six (71.9%) eyes showed misalignment of 5 degrees or less, and 60 (93.8%) eyes showed misalignment of 10 degrees or less. The mean log MAR UCVA at 1st post-op day was 0.172 (SD = 0.02), on 7th post-op day was 0.138 (SD = 0.11), and on 30th post-op day was 0.081 (SD = 0.11). The mean log MAR BCVA at three months was -0.04 (SD = 0.76). We believe that implantation of AcrySof® toric IOL is an effective, safe and predictable method to correct high amounts of corneal astigmatism during cataract surgery.

  20. Profile of refractive errors in European Caucasian children with Autistic Spectrum Disorder; increased prevalence and magnitude of astigmatism.

    PubMed

    Anketell, Pamela M; Saunders, Kathryn J; Gallagher, Stephen; Bailey, Clare; Little, Julie-Anne

    2016-07-01

    Autistic Spectrum Disorder (ASD) is a common neurodevelopmental disorder characterised by impairment of communication, social interaction and repetitive behaviours. Only a small number of studies have investigated fundamental clinical measures of vision including refractive error. The aim of this study was to describe the refractive profile of a population of children with ASD compared to typically developing (TD) children. Refractive error was assessed using the Shin-Nippon NVision-K 5001 open-field autorefractor following the instillation of cyclopentolate hydrochloride 1% eye drops. A total of 128 participants with ASD (mean age 10.9 ± 3.3 years) and 206 typically developing participants (11.5 ± 3.1 years) were recruited. There was no significant difference in median refractive error, either by spherical equivalent or most ametropic meridian between the ASD and TD groups (Spherical equivalent, Mann-Whitney U307 = 1.15, p = 0.25; Most Ametropic Meridian, U305 = 0.52, p = 0.60). Median refractive astigmatism was -0.50DC (range 0.00 to -3.50DC) for the ASD group and -0.50DC (Range 0.00 to -2.25DC) for the TD group. Magnitude and prevalence of refractive astigmatism (defined as astigmatism ≥1.00DC) was significantly greater in the ASD group compared to the typically developing group (ASD 26%, TD 8%, magnitude U305 = 3.86, p = 0.0001; prevalence (χ12=17.71 , p < 0.0001). This is the first study to describe the refractive profile of a population of European Caucasian children with ASD compared to a TD population of children. Unlike other neurodevelopmental conditions, there was no increased prevalence of spherical refractive errors in ASD but astigmatic errors were significantly greater in magnitude and prevalence. This highlights the need to examine refractive errors in this population. © 2016 The Authors Ophthalmic & Physiological Optics © 2016 The College of Optometrists.

  1. Astigmatism among myopics and its changes from childhood to adult age: a 23-year follow-up study.

    PubMed

    Pärssinen, Olavi; Kauppinen, Markku; Viljanen, Anne

    2015-05-01

    To study the prevalence of and changes in astigmatism from the onset of myopia at school age. Two hundred and forty myopic schoolchildren (mean age 10.9 years), with no previous spectacles, were recruited during 1983-1984 to a randomized 3-year clinical trial of bifocal treatment of myopia. Three annual examinations with subjective cycloplegic refraction were performed for 237-238 subjects. Subsequent examinations were performed at the mean ages of 23.2 and 33.9 years for 178 and 163 subjects, and the last examination, including data from prescriptions of different ophthalmologists, for 32 subjects. Corneal topography was studied at baseline, at the 3-year follow-up and at the two adulthood follow-ups. Prevalence and changes in refractive astigmatism (RA), in its polar values J0 and J45, and corneal astigmatism (CA) were studied. Mean RA of the right eye increased during follow-up from 0.26 D (SD) ± 0.30 to 0.79 D ± 0.74. Mean CA was 1.07 D ± 0.74 at study end. The prevalence of RA ≥0.25 or ≥1.00 D increased from 54.9 and 3.8% to 83.4 and 34.4%, respectively. The main direction of the axis of RA and its polar value J0 and CA changed mainly through sphericity, from against the rule (ATR) to with the rule during the follow-up. There was a negative correlation between RA and spherical refraction in the ATR group at end of follow-up. Changes in RA were associated with increase in myopia and with changes in CA. The prevalence and mean amount of RA associated with CA increased, and the axis of astigmatism changed among myopics during the 23-year follow-up. © 2014 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

  2. A fast Gaussian beam tracing method for reflection and refraction of general vectorial astigmatic Gaussian beams from general curved surfaces

    NASA Astrophysics Data System (ADS)

    Rohani, A.; Shishegar, A. A.; Safavi-Naeini, S.

    2004-03-01

    A fast Gaussian beam tracing method for general vectorial astigmatic Gaussian beams based on phase matching has been formulated. Given the parameters of a vectorial Gaussian beam in its principal coordinate system the parameters of the reflected and refracted beams from a general curved surface (with general constitutive parameters) are found. The reflection and transmission of such beams from and through passive photonic structures such as lenses, mirrors and prisms can then be found by considering multiple reflections and transmissions.

  3. Optical coherence tomography with a 2.8-mm beam diameter and sensorless defocus and astigmatism correction.

    PubMed

    Reddikumar, Maddipatla; Tanabe, Ayano; Hashimoto, Nobuyuki; Cense, Barry

    2017-02-01

    An optical coherence tomography (OCT) system with a 2.8-mm beam diameter is presented. Sensorless defocus correction can be performed with a Badal optometer and astigmatism correction with a liquid crystal device. OCT B-scans were used in an image-based optimization algorithm for aberration correction. Defocus can be corrected from ? 4.3 ?? D to + 4.3 ?? D and vertical and oblique astigmatism from ? 2.5 ?? D to + 2.5 ?? D . A contrast gain of 6.9 times was measured after aberration correction. In comparison with a 1.3-mm beam diameter OCT system, this concept achieved a 3.7-dB gain in dynamic range on a model retina. Both systems were used to image the retina of a human subject. As the correction of the liquid crystal device can take more than 60 s, the subject’s spectacle prescription was adopted instead. This resulted in a 2.5 times smaller speckle size compared with the standard OCT system. The liquid crystal device for astigmatism correction does not need a high-voltage amplifier and can be operated at 5 V. The correction device is small ( 9 ?? mm × 30 ?? mm × 38 ?? mm ) and can easily be implemented in existing designs for OCT.

  4. High-cylinder acrylic toric intraocular lenses: a case series of eyes with cataracts and large amounts of corneal astigmatism.

    PubMed

    Cervantes-Coste, Guadalupe; Garcia-Ramirez, Laura; Mendoza-Schuster, Erick; Velasco-Barona, Cecilio

    2012-04-01

    To examine the stability and efficacy of high-cylinder power AcrySof toric intraocular lenses (IOLs), models SN60T6, SN60T7, SN60T8, and SN60T9 (Alcon Laboratories Inc). Eligible eyes had cataract and symmetric corneal astigmatism > 2.25 diopters (D). Outcomes included monocular uncorrected distance visual acuity (UDVA), manifest refraction, and assessment of IOL axis. Nineteen eyes from 14 patients had preoperative corneal astigmatism of 4.00 ± 1.10 D. Postoperatively, residual refractive cylinder was 0.55 ± 0.60 D at 3 months. Uncorrected distance visual acuity was 1.3 ± 0.5 logMAR preoperatively and improved to 0.11 ± 0.09 logMAR 3 months postoperatively (P<.0001). All IOLs were stable within 5°. The IOLs were stable and effective in correcting high amounts of preexisting astigmatism at the time of cataract surgery. Copyright 2012, SLACK Incorporated.

  5. Visual outcomes after balanced salt solution infiltration during lenticule separation in small-incision lenticule extraction for myopic astigmatism.

    PubMed

    Liu, Ting; Zhu, Xiaomin; Chen, Kaijian; Bai, Ji

    2017-07-01

    To evaluate the refractive outcomes of balanced salt solution infiltration during small-incision lenticule extraction (SMILE).This randomized prospective study enrolled 52 patients (104 eyes) with myopic astigmatism. Patients underwent SMILE to correct the myopic astigmatism in Daping Hospital of the Third Military Medical University between January and July 2013. One eye of each patient received traditional SMILE (control group) and the other received a modified SMILE procedure (liquid infiltration group). The corrected distance visual acuity (CDVA), postoperative uncorrected distance visual acuity (UDVA), refraction, wavefront aberration, intraocular pressure (IOP), modulation transfer function (MTF) cut-off frequency, and objective scattering index (OSI) were evaluated.UDVA in the liquid infiltration group was significantly higher than that in the control group at 1 day postoperatively, but not at 1 month after surgery. Moreover, OSI and MTF cut-off frequency in the liquid infiltration group were higher than those in the control group at early follow-up. However, no significant intergroup difference was observed in the OSI and MTF cut-off frequency at 3 months after surgery. In addition, the predictability was better in the liquid infiltration group than in the control group. The changes of horizontal coma in the liquid infiltration group were lesser than those in the control group. However, no intergroup difference was observed in the reduction of IOP at 1 month after surgery.The modified SMILE procedure results in better visual outcomes than did the traditional SMILE procedure when used for treating myopic astigmatism.

  6. The level of improvement of visual acuity in high corneal astigmatism with rigid gas permeable contact lenses.

    PubMed

    Opačić, Dalibor; Miljak, Snježana; Ćuruvija-Opačić, Ksenija

    2015-03-01

    The aim of this study was to calculate the level of improvement of visual acuity comparing the best corrected visual acuity (VA) achieved with spectacles with the best corrected VA achieved with rigid gas permeable (RGP) contact lenses in patients with high, simple or compound corneal astigmatism (myopic, hypermetropic and mixed). The investigation of patients included auto-kerato-refractometry, manual keratometry, corneal topography and visual acuity with Snellen chart. The best corrected VA obtained with spectacles was compared with the best corrected VA obtained with RGP contact lenses in 72 patients (116 eyes). All patients showed a significant improvement in visual acuity with RGP lenses from one to seven lines compared to spectacles (p = 0.0001). Level of improvement in VA represented as the number of lines obtained was as follows: 74 percent of patients got two to four lines more in VA with RGP lenses compared to spectacles, and almost 10 percent of patients got five to seven lines. RGP contact lenses provide a significant improvement in VA compared to VA reached with spectacles in patients with high corneal astigmatism. The benefit in VA with RGP lenses is higher as the astigmatism is higher.

  7. Optical coherence tomography with a 2.8-mm beam diameter and sensorless defocus and astigmatism correction

    NASA Astrophysics Data System (ADS)

    Reddikumar, Maddipatla; Tanabe, Ayano; Hashimoto, Nobuyuki; Cense, Barry

    2017-02-01

    An optical coherence tomography (OCT) system with a 2.8-mm beam diameter is presented. Sensorless defocus correction can be performed with a Badal optometer and astigmatism correction with a liquid crystal device. OCT B-scans were used in an image-based optimization algorithm for aberration correction. Defocus can be corrected from -4.3 D to +4.3 D and vertical and oblique astigmatism from -2.5 D to +2.5 D. A contrast gain of 6.9 times was measured after aberration correction. In comparison with a 1.3-mm beam diameter OCT system, this concept achieved a 3.7-dB gain in dynamic range on a model retina. Both systems were used to image the retina of a human subject. As the correction of the liquid crystal device can take more than 60 s, the subject's spectacle prescription was adopted instead. This resulted in a 2.5 times smaller speckle size compared with the standard OCT system. The liquid crystal device for astigmatism correction does not need a high-voltage amplifier and can be operated at 5 V. The correction device is small (9 mm×30 mm×38 mm) and can easily be implemented in existing designs for OCT.

  8. Refractive Outcomes of 20 Eyes Undergoing ICL Implantation for Correction of Hyperopic Astigmatism.

    PubMed

    Coskunseven, Efekan; Kavadarli, Isilay; Sahin, Onurcan; Kayhan, Belma; Pallikaris, Ioannis

    2017-09-01

    To analyze 1-week, 1-month, and 12-month postoperative refractive outcomes of eyes that under-went ICL implantation to correct hyperopic astigmatism. The study enrolled 20 eyes of patients with an average age of 32 years (range: 21 to 40 years). The outcomes of spherical and cylindrical refraction, uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), vault, and angle parameters were evaluated 1 week, 1 month, and 12 months postoperatively. The preoperative mean UDVA was 0.15 ± 0.11 (decimal) (20/133 Snellen) and increased to 0.74 ± 0.25 (20/27 Snellen) postoperatively, with a change of 0.59 (decimal) (20/33.9 Snellen) (P < .0001), which was statistically significant. The preoperative mean CDVA was 0.74 ± 0.25 (decimal) (20/27 Snellen) and increased to 0.78 ± 0.21 (20/25 Snellen), with a change of 0.03 (decimal) (20/666 Snellen) (P < .052), which was not statistically significant. The mean preoperative sphere was 6.86 ± 1.77 diopters (D) and the mean preoperative cylinder was -1.44 ± 0.88 D. The mean 12-month postoperative sphere decreased to 0.46 ± 0.89 D (P < .001) and cylinder decreased to -0.61 ± 0.46 D (P < .001), with a change of 6.40 D, both of which were statistically significant. The mean 1-month postoperative vault was 0.65 ± 0.13 mm and decreased to 0.613 ± 0.10 mm at 1 year postoperatively, with a change of 0.44 mm (P < .003). The preoperative/12-month and 1-month/12-month trabecular-iris angle (TIA), trabecular-iris space area 500 mm from the scleral spur (TISA500), and angle opening distance 500 mm from the scleral spur (AOD500) values were analyzed nasally, temporally, and inferiorly. All differences were statistically significant between preoperative/12-month analysis. The only differences between 1- and 12-month analysis were on TISA500 inferior (P < .002) and AOD500 nasal (0.031) values. ICL hyperopic toric implantation is a safe method and provides stable refractive outcomes in patients with high hyperopia

  9. Combination of Toric and multifocal intraocular lens implantation in bilateral cataract patients with unilateral astigmatism

    PubMed Central

    Liang, Jing-Li; Tian, Fang; Zhang, Hong; Teng, He

    2016-01-01

    AIM To assess the binocular visual function in bilateral cataract patients with unilateral astigmatism after combined implantations of Toric with multifocal intraocular lens (IOL), and to compare with that of Toric and monofocal IOL implantation. METHODS All the 30 patients with unilateral astigmatism suffered bilateral cataract were randomly divided into two groups: Toric plus multifocal IOL group and Toric plus monofocal IOL group. Uncorrected and corrected visual acuity at distance (5.0 m), intermediate distance (0.6 m), and near (0.33 m), contrast sensitivity, and stereopsis were assessed 6mo after surgery. Patients were also surveyed for visual disturbances and spectacle dependence. RESULTS Binocular uncorrected visual acuity (LogMAR) of Toric/multifocal IOL eyes at distance, intermediate, near were 0.05±0.05, 0.24±0.10, and 0.14±0.06 respectively. The values of Toric plus monofocal IOL eyes were 0.06±0.07, 0.26±0.08, and 0.37±0.10 respectively. These values did not indicate significant differences between two groups with exception of near visual acuity. In the photopic condition (with or without glare), the contrast sensitivity of multifocal IOL eyes was significant lower than the monofocal IOL eyes in 18 cpd. In the mesopic condition, the contrast sensitivity of multifocal group was significant lower than monofocal group in 12 cpd, and in mesopic glare condition, this significant difference was found both in 6 cpd and 12 cpd. The stereopsis of Toric/multifocal IOL eyes decreased slightly (100±80 seconds of arc, t=2.222, P=0.136). Mean near vision for patient satisfaction was statistically significantly higher in Toric/multifocal IOL group patients versus than that in Toric/monofocal IOL group (80% vs 25.5%, P=0.000). Visual disturbance was not noticed in either group. CONCLUSION Although the combination of Toric and multifocal IOL implantation results in compromising stereoacuity, it can still provide patients with high levels of spectacle freedom and

  10. Prevalence of Myopia, Hyperopia and Astigmatism in Non-Hispanic White and Asian Children: Multi-Ethnic Pediatric Eye Disease Study

    PubMed Central

    Wen, Ge; Tarczy-Hornoch, Kristina; McKean-Cowdin, Roberta; Cotter, Susan A.; Borchert, Mark; Lin, Jesse; Kim, Jeniffer; Varma, Rohit

    2013-01-01

    Purpose To determine the age-, gender- and ethnicity-specific prevalence of myopia, hyperopia and astigmatism in Non-Hispanic White (NHW) and Asian preschool children. Design Population-based cross-sectional study. Participants A population based sample of 1501 NHW children and 1507 Asian children aged 6-72 months from Los Angeles County and Riverside County, California. Methods Eligible children underwent an in-home and in-clinic interview and a comprehensive eye examination including cycloplegic auto-refraction from 100 census tracts. Main outcome measures The proportion of children with myopia (spherical equivalent (SE) <=−1.00 diopter (D)), hyperopia (SE >=+2.00) D and cylindrical refractive error >=1.50 D in the worse eye. The astigmatism type was defined as with-the-rule (WTR) (+cylinder axis 90° ± 15°) and against-the-rule (ATR) (+ cylinder axis 180° ± 15°); all other orientations were considered oblique (OBL). Results The prevalence of myopia, hyperopia and astigmatism in NHW children was 1.20% (95% Confidence Interval (CI) = 0.76-1.89%), 25.65% (95% CI= 23.5-27.9%), and 6.33% (95% CI = 5.21-7.68%), respectively. The prevalence of WTR, ATR and OBL astigmatism in NHW children was 4.33%, 1.00% and 1.00% respectively. Prevalence was lower with older age groups for astigmatism (p=0.0002), but not for myopia or hyperopia (p=0.82 and p=0.31, respectively). In Asian children, the prevalence of myopia, hyperopia and astigmatism was 3.98% (95% CI = 3.11-5.09%), 13.47% (95% CI= 11.8-15.3%) and 8.29% (95% CI=7.01-9.80%), respectively. The prevalence of WTR, ATR and OBL astigmatism was 6.50%, 0.80% and 1.00% respectively. The prevalence of hyperopia was higher in girls than boys (p=0.0002), but no significant differences were found for myopia and astigmatism. Conclusion Hyperopia was the most common refractive error in both Asian and NHW children. However, compared to NHW children, myopia was relatively more prevalent, and hyperopia less prevalent, in Asian

  11. Prevalence of Astigmatism in 6 to 72 Months Old African American and Hispanic Children: The Multi-Ethnic Pediatric Eye Disease Study

    PubMed Central

    2010-01-01

    Purpose To determine the age-, gender- and ethnicity-specific prevalence of astigmatism in African American and Hispanic children aged 6 to 72 months. Design Population-based cross-sectional study. Participants The Multi-Ethnic Pediatric Eye Disease Study is a population-based evaluation of the prevalence of vision disorders in children ages 6–72 months in Los Angeles County, California. Seventy-seven percent of eligible children completed a comprehensive eye exam. This report provides the results from 2994 African American and 3030 Hispanic children. Methods Eligible children in 44 census tracts were identified during an in-home interview and scheduled for a comprehensive eye examination and in-clinic interview. Cycloplegic auto-refraction was used to determine refractive error. Main outcome measures The proportion of children with astigmatism defined as cylindrical refractive error ≥1.50 diopters (D) in the worse eye. The astigmatism type was defined as with-the-rule (WTR) (+ cylinder axis 90° ± 15°) and against-the-rule (ATR) (+ cylinder axis 180° ± 15°); all other orientations were considered oblique (OBL). The prevalence of astigmatism and its types were also determined for worse eye cylindrical refractive error ≥3.00 D. Results Prevalence of astigmatism (≥1.50 D) was higher in Hispanic children compared to African American children (16.8% vs. 12.7%, respectively; P<0.0001). Hispanic children also showed a higher prevalence of astigmatism (≥3.00 D) than African American children (2.9% vs. 1.0% respectively; P<0.0001). The prevalence of astigmatism ≥1.50 D showed a significant decreasing trend with age (P<0.0001). The prevalence of WTR, ATR and OBL astigmatism ≥1.50 D was 13.9%, 0.6% and 2.2%, respectively, in Hispanic children, and 7.8%, 2.2% and 2.7%, respectively, in African American children. Conclusion We observed ethnicity-related differences in astigmatism prevalence in preschool children. The age-related decrease in astigmatism

  12. Comparison of surgically induced astigmatism between femtosecond laser and manual clear corneal incisions for cataract surgery.

    PubMed

    Diakonis, Vasilios F; Yesilirmak, Nilufer; Cabot, Florence; Kankariya, Vardhaman P; Kounis, George A; Warren, Daniel; Sayed-Ahmed, Ibrahim O; Yoo, Sonia H; Donaldson, Kendall

    2015-10-01

    To assess the surgically induced corneal astigmatism (SIA) introduced by femtosecond laser-assisted clear corneal incisions (CCIs) for cataract extraction and to compare it with the SIA of manually created CCIs. Bascom Palmer Eye Institute, Miller School of Medicine, Miami, Florida, USA. Prospective nonrandomized comparative case series. Eyes received femtosecond laser-assisted CCIs (Group 1) or manual CCIs (Group 2). The surgical plan included 1 primary and 1 secondary port; the sites of the incisions were the same in both groups and were diametrically opposed between the right eye and left eye. The SIA was assessed using the preoperative and 1-month postoperative keratometric values obtained from corneal topography examinations. This study included 72 eyes of 68 patients with a mean age of 69.0 years ± 9.87 (SD) (range 36 to 90 years). Thirty-six eyes received femtosecond laser-assisted CCIs (Group 1) and 36 received manual CCIs (Group 2). The mean preoperative topographic corneal astigmatism was -1.19 ± 0.68 diopters (D) (range 0 to 2.50 D) and -0.92 ± 0.63 D (range 0.10 to 2.45 D) for Group 1 and Group 2, respectively, whereas, 1 month after cataract surgery, it was -1.16 ± 0.63 D (range 0.20 to 2.57 D) and -0.95 ± 0.64 D (range 0.21 to 2.37 D), respectively. Multivariate vector analysis revealed no statistically significant difference between the 2 groups for preoperative astigmatism, postoperative astigmatism, and SIA (P > .05 for all comparisons between Group 1 and Group 2). Femtosecond laser-assisted and manual corneal incisions for cataract surgery did not appear to significantly alter corneal astigmatism, whereas they showed comparable SIA. Drs. Yoo and Donaldson are speakers for and consultants to Alcon Surgical, Inc., and Abbott Medical Optics, Inc. No other author has a financial or proprietary interest in any material or method mentioned. Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  13. Macroscopic three-dimensional particle location using stereoscopic imaging and astigmatic aberrations.

    PubMed

    Fuchs, Thomas; Hain, Rainer; Kähler, Christian J

    2014-12-15

    This Letter presents a stereoscopic imaging concept for measuring the locations of particles in three-dimensional space. The method is derived from astigmatism particle tracking velocimetry (APTV), a powerful technique that is capable of determining 3D particle locations with a single camera. APTV locates particle xy coordinates with high accuracy, while the particle z coordinate has a larger location uncertainty. This is not a problem for 3D2C (i.e., three dimensions, two velocity components) measurements, but for highly three-dimensional flows, it is desirable to measure three velocity components with similar accuracy. The stereoscopic APTV approach discussed in this report has this capability. The technique employs APTV for giving an initial estimate of the particle locations. With this information, corresponding particle images on both sensors of the stereoscopic imaging system are matched. Particle locations are then determined by mapping the two particle image sensor locations to physical space. The measurement error of stereo APTV, determined by acquiring images of 1-μm DEHS particles in a 40 mm×40 mm×20 mm measurement volume in air at Δxyz→0 between two frames, is less than 0.012 mm for xy and 0.025 mm for z. This error analysis proves the excellent suitability of stereo APTV for the measurement of three-dimensional flows in macroscopic domains.

  14. Advanced astigmatism-corrected tandem Wadsworth mounting for small-scale spectral broadband imaging spectrometer.

    PubMed

    Lei, Yu; Lin, Guan-yu

    2013-01-01

    Tandem gratings of double-dispersion mount make it possible to design an imaging spectrometer for the weak light observation with high spatial resolution, high spectral resolution, and high optical transmission efficiency. The traditional tandem Wadsworth mounting is originally designed to match the coaxial telescope and large-scale imaging spectrometer. When it is used to connect the off-axis telescope such as off-axis parabolic mirror, it presents lower imaging quality than to connect the coaxial telescope. It may also introduce interference among the detector and the optical elements as it is applied to the short focal length and small-scale spectrometer in a close volume by satellite. An advanced tandem Wadsworth mounting has been investigated to deal with the situation. The Wadsworth astigmatism-corrected mounting condition for which is expressed as the distance between the second concave grating and the imaging plane is calculated. Then the optimum arrangement for the first plane grating and the second concave grating, which make the anterior Wadsworth condition fulfilling each wavelength, is analyzed by the geometric and first order differential calculation. These two arrangements comprise the advanced Wadsworth mounting condition. The spectral resolution has also been calculated by these conditions. An example designed by the optimum theory proves that the advanced tandem Wadsworth mounting performs excellently in spectral broadband.

  15. Inspection focus technology of space tridimensional mapping camera based on astigmatic method

    NASA Astrophysics Data System (ADS)

    Wang, Zhi; Zhang, Liping

    2010-10-01

    The CCD plane of the space tridimensional mapping camera will be deviated from the focal plane(including the CCD plane deviated due to camera focal length changed), under the condition of space environment and vibration, impact when satellite is launching, image resolution ratio will be descended because defocusing. For tridimensional mapping camera, principal point position and focal length variation of the camera affect positioning accuracy of ground target, conventional solution is under the condition of vacuum and focusing range, calibrate the position of CCD plane with code of photoelectric encoder, when the camera defocusing in orbit, the magnitude and direction of defocusing amount are obtained by photoelectric encoder, then the focusing mechanism driven by step motor to compensate defocusing amount of the CCD plane. For tridimensional mapping camera, under the condition of space environment and vibration, impact when satellite is launching, if the camera focal length changes, above focusing method has been meaningless. Thus, the measuring and focusing method was put forward based on astigmation, a quadrant detector was adopted to measure the astigmation caused by the deviation of the CCD plane, refer to calibrated relation between the CCD plane poison and the asrigmation, the deviation vector of the CCD plane can be obtained. This method includes all factors caused deviation of the CCD plane, experimental results show that the focusing resolution of mapping camera focusing mechanism based on astigmatic method can reach 0.25 μm.

  16. Non-astigmatic imaging with matched pairs of spherically bent reflectors

    DOEpatents

    Bitter, Manfred Ludwig [Princeton, NJ; Hill, Kenneth Wayne [Plainsboro, NJ; Scott, Steven Douglas [Wellesley, MA; Feder, Russell [Newton, PA; Ko, Jinseok [Cambridge, MA; Rice, John E [N. Billerica, MA; Ince-Cushman, Alexander Charles [New York, NY; Jones, Frank [Manalapan, NJ

    2012-07-10

    Arrangements for the point-to-point imaging of a broad spectrum of electromagnetic radiation and ultrasound at large angles of incidence employ matched pairs of spherically bent reflectors to eliminate astigmatic imaging errors. Matched pairs of spherically bent crystals or spherically bent multi-layers are used for X-rays and EUV radiation; and matched pairs of spherically bent mirrors that are appropriate for the type of radiation are used with microwaves, infrared and visible light, or ultrasound. The arrangements encompass the two cases, where the Bragg angle--the complement to the angle of incidence in optics--is between 45.degree. and 90.degree. on both crystals/mirrors or between 0.degree. and 45.degree. on the first crystal/mirror and between 45.degree. and 90.degree. on the second crystal/mirror, where the angles of convergence and divergence are equal. For x-rays and EUV radiation, also the Bragg condition is satisfied on both spherically bent crystals/multi-layers.

  17. [Distribution and compensation mechanism of aberrations between anterior and posterior surface of the cornea in myopia and myopic astigmatism eyes].

    PubMed

    Li, X J; Wang, Y; Wu, Y N; Wu, W J; Yu, C J; Xu, L L

    2016-11-11

    Objective: To study the compensation mechanism of aberrations between anterior and posterior corneal surface, and to investigate the correlations between corneal aberrations and K values, intraocular pressure and central corneal thickness. Methods: One hundred and sixty-one subjects (300 eyes) with myopia and myopic astigmatism were recruited randomly. Corneal aberrations (anterior, posterior and total) in three different optical zones (2 mm, 4 mm, and 6 mm) centered on the corneal vertex were assessed with a corneal topographer (Sirius). We also calculated compensation factors (CFs) as a measure of the relative efficiency of the aberration compensation mechanism. Astigmatism was divided into corneal astigmatism and non-corneal astigmatism. Mann-Whitney U test was utilized for the comparison of different aberrations and CFs between the two astigmatism groups. Spearman correlation was applied to analyze the correlations between corneal aberrations and K values, intraocular pressure and central corneal thickness. Results: As the order of the aberrations elevated from the second to the seventh, the RMS values decreased significantly. The larger the optical zone, the greater the values of aberrations and the lower the percentage of the compensation mechanism among all the Zernike terms. At the same time, as the order of the aberrations increased, the predominance of the compensation mechanism was increasingly obvious. Slight compensation of spherical aberration (Z4(0)) was observed in the peripheral. In the center of the analyzing zones (2 mm), compensation mechanism represented in coma (Z3(±1)), and it disappeared in the peripheral. We detected slight compensation of the corneal astigmatism (Z2(±2)) in the surrounding zone, although the compensation factors were closed to zero in diverse optical zones. Superposition was found in trefoil (Z3(±3)) straightly. Nevertheless, a tendency towards compensation was discovered with the enlargement of the optical zones. And

  18. A Critical Evaluation of Refractive Outcomes Following LASIK for Moderate to High Astigmatism Using Two Excimer Laser Platforms.

    PubMed

    Patel, Sudi; Bohac, Maja; Biscevic, Alma; Koncarevic, Mateja; Anticic, Marija; Gabric, Nikica

    2017-02-01

    To calculate the surgically induced astigmatism (SIA) following LASIK and identify any association between SIA and the target induced astigmatism (TIA) at 1 year postoperatively. The SIA was calculated using the TIA and residual astigmatism values for [A] myopic astigmatism and [B] mixed astigmatism treated with either the [I] WaveLight Allegretto EyeQ 400-Hz (Alcon Laboratories, Inc. Fort Worth, TX) or [II] Schwind Amaris 750S (Schwind eye-tech-solutions, Kleinostheim, Germany) platforms. The TIA and corresponding SIA results were analyzed using various techniques. Key findings were the negative SIA power (y1) was significantly correlated with negative TIA power (x1) and sine of the TIA axis (x2) as follows: [A] I, y1= 0.829x1-0.403x2-0.325 (F = 87.76, r = 0.804, P < .001, n = 127); II, y1= 0.891x1-0.037x2-0.192 (F = 240.06, r = 0.901, P < .001, n = 119) and [B] I, y1= 1.063x1+0.233x2+0.411 (F = 990.99, r = 0.881, P < .001, n = 61); II, y1= 1.029x1-0.115x2+0.322 (F = 270.12, r = 0.908, P < 0.001, n = 111). The sine of negative SIA axis (y2) was significantly correlated with negative TIA power (x1) and TIA axis (x2) as follows: [A] I, y2 = 0.951x2-0.007x1+0.008 (F = 446.58, r = 0.950, P < .001, n = 127); II, y2 = 0.856x2+0.007x1+0.105 (F = 277.18, r = 0.912, P< .001, n = 119) and [B] I, y2 = 0.953x2+0.009x1+0.075 (F = 362.6, r = 0.963, P < .001, n = 61); II, y2 = 0.977x2-0.004x1+0.002 (F = 2910.9, r = 0.990, P < .001, n = 111). The predicted SIA power was up to 12% less than expected in cases of -6.00 diopters cylinder treated for myopic astigmatism using the Allegretto platform. The mean predicted angle of error (the angle between the SIA and TIA axes) was less than 4°, increasing to 12° for against-the-rule astigmatism. The Allegretto platform tended toward a clockwise axis rotational error, whereas the Amaris platform tended toward the opposite. [J Refract Surg. 2017;33(2):104-109.]. Copyright 2017, SLACK Incorporated.

  19. Comparison of Toric Foldable Iris-Fixated Phakic Intraocular Lens Implantation and Limbal Relaxing Incisions for Moderate-to-High Myopic Astigmatism.

    PubMed

    Lee, Jeihoon; Lee, Hun; Kang, David Sung Yong; Choi, Jin Young; Kim, Eung Kweon; Kim, Tae Im

    2016-11-01

    To compare the effectiveness of toric foldable iris-fixated phakic intraocular lens (pIOL) implantation and non-toric foldable iris-fixated pIOL implantation with limbal relaxing incisions (LRIs) for correcting moderate-to-high astigmatism in myopic eyes. The medical records of 146 patients (195 eyes) with myopic astigmatism who underwent toric foldable iris-fixated pIOL implantation (toric group; 94 eyes) or non-toric foldable iris-fixated pIOL implantation with concurrent LRIs (LRI group; 101 eyes) were retrospectively reviewed. For subgroup analysis, the two groups were subdivided according to preoperative astigmatic severity [moderate, 2.00 to <3.00 diopters (D); high, 3.00-4.00 D]. Visual and astigmatic outcomes were compared 6 months postoperatively. The uncorrected distance visual acuity was at least 20/25 in 100% and 98% of the toric and LRI group eyes, respectively. The toric group had lower mean residual cylindrical error (-0.67±0.39 D vs. -1.14±0.56 D; p<0.001) and greater mean cylindrical error change (2.17±0.56 D vs. 1.63±0.72 D; p<0.001) than the LRI group, regardless of the preoperative astigmatic severity. The mean correction index (1.10±0.16 vs. 0.72±0.24; p<0.001) and success index (0.24±0.14 vs. 0.42±0.21; p<0.001) also differed significantly between the groups. Both surgical techniques considerably reduced astigmatism and had comparable visual outcomes. However, toric foldable iris-fixated pIOL implantation was more reliable for correcting moderate-to-high astigmatism in myopic eyes.

  20. The Unevenness and Non-orthogonal State of Distribution of Corneal Thickness and the Influence on Correction of Myopic Astigmatism by LASEK.

    PubMed

    Wang, Shulin; Wang, Xin; Liu, Mingna; Wang, Haiying; Li, Jing; Shi, Weiyun

    2015-09-01

    To observe and calculate the unevenness and the non-orthogonal state of distribution of corneal thickness and the relationship between them using Pentacam and to investigate the influence of unevenness and the non-orthogonal state on correction of myopic astigmatism by laser subepithelial keratomileusis (LASEK). 230 eyes with myopic astigmatism treated with LASEK were divided into two groups: 114 eyes as the low astigmatism group (-0.25 to -0.75 DC) and 116 eyes as the midrange-high astigmatism group (-1.00 to -4.50 DC). With the help of the diagram of keratoconus evaluation program of the Pentacam, the D 3.0 and D 6.5 were calculated for the index of distribution of unevenness of the corneal thickness, and the absolute value of the angle between the maximum and minimum progression-index orientation (M 90) for the index of non-orthogonal states. The correction of myopic astigmatism by LASEK was based on standard vector analysis and power vector analysis. The follow-up period was for 3 months. The preoperative M 90 was 22.14° ± 20.87°, D 6.5 was 58.66 ± 21.32 μm, and D 3.0 was 16.11 ± 4.28 μm for the 230 eyes that were tested. The D 6.5 of low astigmatism group (55.62 ± 20.81) μm was significantly lower than that of midrange-high astigmatism group (61.65 ± 21.48) μm (P < 0.05). Of the 230 eyes, the M 90 was positively correlated with D 6.5 (r = 0.37, P < 0.001), and D 6.5 was positively correlated with D 3.0 (r = 0.56, P < 0.001). 3 months postoperatively, the absolute error vector (|EV|) of low astigmatism group (0.46 ± 0.34) was significantly lower than that of midrange-high astigmatism group (0.53 ± 0.29) (P < 0.01). The error of magnitude of low astigmatism group (-0.10 ± 0.31) was significantly lower than that of midrange-high astigmatism group (0.08 ± 0.41) (P < 0.001). The absolute error of angle (|EA|) of low astigmatism group (26.10 ± 27.24) was significantly higher than that of midrange

  1. Preliminary study of the association between corneal histocytological changes and surgically induced astigmatism after phacoemulsification.

    PubMed

    Du, Xing; Zhao, Guiqiu; Wang, Qing; Yang, Xian; Gao, Ang; Lin, Jing; Wang, Qian; Xu, Qiang

    2014-11-20

    Surgically induced astigmatism (SIA) was one of the factors that influences the desirable refractive outcome, and it was related to the length, type, location, structure of the incision and to the suture closure technique, etc. The aim was to evaluate the association of corneal histocytological changes with SIA after phacoemulsification. The study enrolled 68 cases of cataract patient (68 eyes). Corneal histocytological parameters at corneal incision, central cornea and contralateral incision obtained by confocal microscope through focusing (CMTF) were compared preoperatively and 1 week, 2 weeks, 1 month, 3 months and 6 months postoperatively. These biometric parameters included the endothelial cell density, keratocyte density of posterior stromal layer, and the morphological changes. SIA was calculated by Jaffe's vector analysis. 1 From preoperatively to 1 week, 2 weeks, 1 month, 3 months and 6 months postoperatively, the endothelail cell density was decreased significantly (p < 0.05). Keratocyte density of posterior stroma layer was increased significantly only at 1 week, 2 weeks, 1 month, 3 months postoperatively (p <0.05), but not statistically significant (p = 0.173) at 6 months postoperatively compared to preoperative values. 2 The histocytological observations indicated that the morphology changed significantly postoperatively at the corneal incision, including the cell absent area, wave-like area, dot-like and mass-like hyperreflection, stripe-like absent area, in the endothelial layer, and the keratocyte activation, microfolds, irregular hyporeflective or hyperreflective belt, and a little dot-like hyperreflection in the posterior stroma layer. 3 The reduction of the endothelial cell density at the corneal incision at 1 week, 2 weeks, 1 month postoperatively, were positively correlated with SIA (P1 week = 0.003, P2 weeks = 0.003, P1 month = 0.032), while others were not associated with SIA statistically. The reduction of endothelail cell density and the

  2. Help from a Hindrance: Using Astigmatism in Round Capillaries To Study Contact Angles and Wetting Layers.

    PubMed

    Hobeika, Nelly; Bouriat, Patrick; Touil, Abdelhafid; Broseta, Daniel; Brown, Ross; Dubessy, Jean

    2017-05-30

    Round glass capillaries are a basic tool in soft-matter science, but often are shunned due to the astigmatism they introduce in micrographs. Here, we show how refraction in a capillary can be a help instead of a hindrance to obtain precise and sensitive information on two important interfacial properties: the contact angle of two immiscible fluids and the presence of thin films on the capillary wall. Understanding optical cusps due to refraction allows direct mesurement of the inner diameter of a capillary at the meniscus, which, with the height of the meniscus cap, determines the contact angle. The meniscus can thus be measured without intrusive additives to enhance visibility, such as dyes or calibrated particles, in uniform, curved, or even tapered capillaries or under demanding conditions not accessible by conventional methods, such as small volumes (μL), high temperatures, or high pressures. We further elicit the conditions for strong internal reflection on the inner capillary wall, involving the wall and fluid refractive indices and the wall thickness, and show how to choose the capillary section to detect thin (submicron) layers on the wall, by the contribution of total internal reflection to the cusps. As examples, we report the following: (i) CO2-water or -brine contact angles at glass interfaces, measured at temperatures and pressures up to 200 °C and 600 bar, revealing an effect apparently so far unreported-the decrease in the water-wet character of glass, due to dissolved salts in brine, is strongly reduced at high temperatures, where contact angles converge toward the values in pure water; (ii) A tenuous gas hydrate layer growing from the water-guest contact line on glass, invisible in transmission microscopy but prominent in the cusps due to total internal reflection.

  3. 3D multifocus astigmatism and compressed sensing (3D MACS) based superresolution reconstruction

    PubMed Central

    Huang, Jiaqing; Sun, Mingzhai; Gumpper, Kristyn; Chi, Yuejie; Ma, Jianjie

    2015-01-01

    Single molecule based superresolution techniques (STORM/PALM) achieve nanometer spatial resolution by integrating the temporal information of the switching dynamics of fluorophores (emitters). When emitter density is low for each frame, they are located to the nanometer resolution. However, when the emitter density rises, causing significant overlapping, it becomes increasingly difficult to accurately locate individual emitters. This is particularly apparent in three dimensional (3D) localization because of the large effective volume of the 3D point spread function (PSF). The inability to precisely locate the emitters at a high density causes poor temporal resolution of localization-based superresolution technique and significantly limits its application in 3D live cell imaging. To address this problem, we developed a 3D high-density superresolution imaging platform that allows us to precisely locate the positions of emitters, even when they are significantly overlapped in three dimensional space. Our platform involves a multi-focus system in combination with astigmatic optics and an ℓ1-Homotopy optimization procedure. To reduce the intrinsic bias introduced by the discrete formulation of compressed sensing, we introduced a debiasing step followed by a 3D weighted centroid procedure, which not only increases the localization accuracy, but also increases the computation speed of image reconstruction. We implemented our algorithms on a graphic processing unit (GPU), which speeds up processing 10 times compared with central processing unit (CPU) implementation. We tested our method with both simulated data and experimental data of fluorescently labeled microtubules and were able to reconstruct a 3D microtubule image with 1000 frames (512×512) acquired within 20 seconds. PMID:25798314

  4. Enhanced cooling of Yb:YLF using astigmatic Herriott cell (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Gragossian, Aram; Meng, Junwei; Ghasemkhani, Mohammadreza; Albrecht, Alexander R.; Tonelli, Mauro; Sheik-Bahae, Mansoor

    2017-02-01

    Optical refrigeration of solids requires crystals with exceptional qualities. Crystals with external quantum efficiencies (EQE) larger than 99% and background absorptions of 4×10-4cm-1 have been cooled to cryogenic temperatures using non resonant cavities. Estimating the cooling efficiency requires accurate measurements of the above mentioned quantities. Here we discuss measurements of EQE and background absorption for two high quality Yb:YLF samples. For any given sample, to reach minimum achievable temperatures heat generated by fluorescence must be removed from the surrounding clamshell and more importantly, absorption of the laser light must be maximized. Since the absorption coefficient drops at lower temperatures the only option is to confine laser light in a cavity until almost 100% of the light is absorbed. This can be achieved by placing the crystal between a cylindrical and spherical mirror to form an astigmatic Herriott cell. In this geometry light enters through a hole in the middle of the spherical mirror and if the entrance angle is correct, it can make as many round trips as required to absorb all the light. At 120 K 60 passes and 150 passes at 100K ensures more than 95% absorption of the laser light. 5 and 10% Yb:YLF crystals placed in such a cell cool to sub 90K temperatures. Non-contact temperature measurements are more challenging for such a geometry. Reabsorption of fluorescence for each pass must be taken into account for accurate temperature measurements by differential luminescence thermometry (DLT). Alternatively, we used part of the spectrum that is not affected by reabsorption.

  5. Transmissive liquid-crystal device correcting primary coma aberration and astigmatism in laser scanning microscopy

    NASA Astrophysics Data System (ADS)

    Tanabe, Ayano; Hibi, Terumasa; Ipponjima, Sari; Matsumoto, Kenji; Yokoyama, Masafumi; Kurihara, Makoto; Hashimoto, Nobuyuki; Nemoto, Tomomi

    2016-03-01

    Laser scanning microscopy allows 3D cross-sectional imaging inside biospecimens. However, certain aberrations produced can degrade the quality of the resulting images. We previously reported a transmissive liquid-crystal device that could compensate for the predominant spherical aberrations during the observations, particularly in deep regions of the samples. The device, inserted between the objective lens and the microscope revolver, improved the image quality of fixed-mouse-brain slices that were observed using two-photon excitation laser scanning microscopy, which was originally degraded by spherical aberration. In this study, we developed a transmissive device that corrects primary coma aberration and astigmatism, motivated by the fact that these asymmetric aberrations can also often considerably deteriorate image quality, even near the sample surface. The device's performance was evaluated by observing fluorescent beads using single-photon excitation laser scanning microscopy. The fluorescence intensity in the image of the bead under a cover slip tilted in the y-direction was increased by 1.5 times after correction by the device. Furthermore, the y- and z-widths of the imaged bead were reduced to 66% and 65%, respectively. On the other hand, for the imaged bead sucked into a glass capillary in the longitudinal x-direction, correction with the device increased the fluorescence intensity by 2.2 times compared to that of the aberrated image. In addition, the x-, y-, and z-widths of the bead image were reduced to 75%, 53%, and 40%, respectively. Our device successfully corrected several asymmetric aberrations to improve the fluorescent signal and spatial resolution, and might be useful for observing various biospecimens.

  6. Correction of hyperopia with astigmatism following radial keratotomy with daily disposable plus spherical contact lens: a case report.

    PubMed

    Chen, Yun-Wen; Lee, Jiahn-Shing; Hou, Chiun-Ho; Lin, Ken-Kuo

    2017-08-30

    To report the refractive correction in a case of hyperopia and astigmatism following radial keratotomy. A case report. A 47-year-old woman, who had undergone refractive surgery for radial keratotomy in both eyes 22 years before the present study, presented to our clinic with blurred vision. Her best corrected visual acuity, with spectacle correction of +3.50 DS/-1.50 DCX130° in the right eye and +3.75 DS/-1.50 DCX80° in the left eye, was 0.2 logMAR and 0.3 logMAR, respectively. Her keratometric readings were 35.75 D/36.75 D at 74° and 35.25 D/36.25 D at 61°, respectively. Prompted by intolerance to glasses, the patient requested for contact lenses. First, we applied a rigid, gas-permeable contact lens. However, we noted poor fitting due to central corneal flattening. Subsequently, we applied a conventional plus spherical soft contact lens (PSSCL), which is thick in the center and can therefore correct hyperopia and low-grade astigmatism simultaneously. The conventional PSSCL showed slightly inferior decentration, with good movement, and the patient was satisfied with it. After ascertaining the patient's living habits, we decided that a daily disposable soft contact lens would most meet her needs. The final prescription was a daily disposable PSSCL; the patient was satisfied with her corrected visual acuity of 0.0 logMAR in the right eye and 0.0 logMAR in left eye. Her daily disposable PSSCL-corrected visual acuity was stable during the 10-month follow-up. For patients displaying hyperopia with astigmatism following radial keratotomy, the PSSCL may confer better corrected visual acuity and acceptability.

  7. Combining primary and piggyback intraocular lenses to treat extreme myopic astigmatism in stable keratoconus following cataract surgery.

    PubMed

    Goh, Yi Wei; Misra, Stuti; Patel, Dipika V; McGhee, Charles N J

    2013-03-01

    The majority of those with keratoconus can maximise visual acuity with spectacle or contact lens correction as they age; however, as subjects enter their sixties, cataracts may supervene and contact lens tolerance diminishes with consequent reduction in visual acuity. Following cataract extraction, the complex refractive error associated with keratoconus may not be readily corrected by an intraocular lens alone. This report highlights the planned implantation of a primary posterior chamber toric intraocular lens with a secondary piggyback, sulcus-based, intraocular lens in advanced but stable keratoconus with extreme myopic astigmatism and cataract. © 2013 The Authors. Clinical and Experimental Optometry © 2013 Optometrists Association Australia.

  8. Propagation of partially coherent twisted anisotropic Gaussian Schell-model beams through an apertured astigmatic optical system.

    PubMed

    Cai, Yangjian; Hu, Li

    2006-03-15

    By expanding the hard-aperture function into a finite sum of complex Gaussian functions, we derived an approximate analytical formula for a partially coherent twisted anisotropic Gaussian Schell-model (AGSM) beam propagating through an apertured paraxial general astigmatic (GA) optical system by use of a tensor method. The results obtained by using the approximate analytical formula are in good agreement with those obtained by using the numerical integral calculation. Our formulas avoid time-consuming numerical integration and provide a convenient and effective way for studying the propagation and transformation of a partially coherent twisted AGSM beam through an apertured paraxial GA optical system.

  9. Design and Performance Assessment of a Stable Astigmatic Herriott Cell for Trace Gas Measurements on Airborne Platforms

    NASA Technical Reports Server (NTRS)

    Dyroff, Christoph; Fried, Alan; Richter, Dirk; Walega, James G.; Zahniser, Mark S.; McManus, J. Barry

    2005-01-01

    The present paper discusses a new, more stable, astigmatic Herriott cell employing carbon fiber stabilizing rods. Laboratory tests using a near-IR absorption feature of CO at 1564.168-nm revealed a factor of two improvement in measurement stability compared with the present commercial design when the sampling pressure was changed by +/-2 Torr around 50 Torr. This new cell should significantly enhance our efforts to measure trace gases employing pathlengths of 100 to 200-meters on airborne platforms with minimum detectable line center absorbances of less than 10(exp -6).

  10. Design and performance of an astigmatism-compensated self-mode-locked ring-cavity Ti:sapphire laser

    SciTech Connect

    Shen, Y.; Dai, J.; Wang, Q.

    1996-12-31

    Based on the nonlinear ABCD matrix and the renormalized q-parameter for Gaussian-beam propagation, self-focusing in conjunction with a spatial gain profile for self-mode locking in a ring-cavity Ti:sapphire laser is analyzed. In the experiment, an astigmatism-compensated self-mode-locked ring-cavity Ti:sapphire laser is demonstrated, and self-mode-locked operation is achieved in both bidirection and unidirection with pulse durations as short as 36 fs and 32 fs, respectively. The experimental observations are in good agreement with theoretical predictions.

  11. Air bubble in anterior chamber as indicator of full-thickness incisions in femtosecond-assisted astigmatic keratotomy.

    PubMed

    Vaddavalli, Pravin K; Hurmeric, Volkan; Yoo, Sonia H

    2011-09-01

    Femtosecond-assisted astigmatic keratotomy is predictable and precise but may occasionally lead to a full-thickness incision on the cornea and the attendant complications. The presence of an air bubble in the anterior chamber soon after creation of the keratotomy by the femtosecond laser may indicate a full-thickness incision. We present a case in which recognition of this clinical finding early in the procedure might have prevented undesirable complications, such as leakage of aqueous and the potential for intraocular infection. Copyright © 2011 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  12. The effect of three-fold astigmatism on measurements of grain boundary volume expansion by high-resolution transmission electron microscopy.

    SciTech Connect

    Merkle, K. L.; Csencsits, R.; Rynes, K. L.; Withrow, J. P.; Stadelmann, P. A.; Materials Science Division; Batiment MXIC

    1998-04-01

    In the absence of high-order aberrations, the lattice fringe technique should allow measurement of grain boundary rigid-body displacements to accuracies about an order of magnitude better than the point-to-point resolution of the transmission electron microscope. The three-fold astigmatism, however, introduces shifts of the lattice fringe pattern that depend on the orientation of the lattice relative to the direction of the three-fold astigmatism and thus produces an apparent shift between the two grains bordering the grain boundary. By image simulation of grain boundary model structures, the present paper explores the effect of these extraneous shifts on grain boundary volume expansion measurements. It is found that the shifts depend, among others, on zone axis direction and the magnitude of the lattice parameter. For many grain boundaries of interest, three-fold astigmatism correction to better than 100 nm appears necessary to achieve the desired accuracies.

  13. Prevalence and associations of anisometropia and aniso‐astigmatism in a population based sample of 6 year old children

    PubMed Central

    Huynh, S C; Wang, X Y; Ip, J; Robaei, D; Kifley, A; Rose, K A; Mitchell, P

    2006-01-01

    Aim To study the distribution of anisometropia and aniso‐astigmatism in young Australian children, together with clinical and ocular biometry relations. Method The Sydney Myopia Study examined 1765 predominantly 6 year old children from 34 randomly selected Sydney schools during 2003–4. Keratometry, cycloplegic autorefraction, and questionnaire data were collected. Results Spherical equivalent (SE) anisometropia (⩾1 dioptre) prevalence was 1.6% (95% confidence interval (CI) 1.1% to 2.4%). Aniso‐astigmatism (⩾1D) prevalence was 1.0% (CI: 0.6% to 1.6%). Both conditions were significantly more prevalent among moderately hyperopic (SE ⩾2.0D) than mildly hyperopic (SE 0.5–1.9D) children. Myopic children (SE ⩽−0.5D) had higher anisometropia prevalence. Neither condition varied by age, sex, or ethnicity. In multivariate analyses, anisometropia was significantly associated with amblyopia, odds ratio (OR) 29, (CI: 8.7 to 99), exotropia (OR 7.7, CI: 1.2 to 50), and neonatal intensive care unit (NICU) admission (OR 3.6, CI: 1.1 to 12.6). Aniso‐astigmatism was significantly associated with amblyopia (OR 8.2, CI: 1.4 to 47), maternal age >35 years (OR 4.0, CI: 1.3 to 11.9), and NICU admission (OR 4.6, CI: 1.2 to 17.2). Anisometropia resulted from relatively large interocular differences in axial length (p<0.0001) and anterior chamber depth (p = 0.0009). Aniso‐astigmatism resulted from differences in corneal astigmatism (p<0.0001). Conclusion In this predominantly 6 year old population, anisometropia and aniso‐astigmatism were uncommon, had important birth and biometry associations, and were strongly related to amblyopia and strabismus. PMID:16622090

  14. Clinical utility of ocular residual astigmatism and topographic disparity vector indexes in subclinical and clinical keratoconus.

    PubMed

    Piñero, David P; Pérez-Cambrodí, Rafael J; Soto-Negro, Roberto; Ruiz-Fortes, Pedro; Artola, Alberto

    2015-12-01

    We aimed to characterize the distribution of the vector parameters ocular residual astigmatism (ORA) and topography disparity (TD) in a sample of clinical and subclinical keratoconus eyes, and to evaluate their diagnostic value to discriminate between these conditions and healthy corneas. This study comprised a total of 43 keratoconic eyes (27 patients, 17-73 years) (keratoconus group), 11 subclinical keratoconus eyes (eight patients, 11-54 years) (subclinical keratoconus group) and 101 healthy eyes (101 patients, 15-64 years) (control group). In all cases, a complete corneal analysis was performed using a Scheimpflug photography-based topography system. Anterior corneal topographic data was imported from it to the iASSORT software (ASSORT Pty. Ltd), which allowed the calculation of ORA and TD. Mean magnitude of the ORA was 3.23 ± 2.38, 1.16 ± 0.50 and 0.79 ± 0.43 D in the keratoconus, subclinical keratoconus and control groups, respectively (p < 0.001). Mean magnitude of the TD was 9.04 ± 8.08, 2.69 ± 2.42 and 0.89 ± 0.50 D in the keratoconus, subclinical keratoconus and control groups, respectively (p < 0.001). Good diagnostic performance of ORA (cutoff point: 1.21 D, sensitivity 83.7 %, specificity 87.1 %) and TD (cutoff point: 1.64 D, sensitivity 93.3 %, specificity 92.1 %) was found for the detection of keratoconus. The diagnostic ability of these parameters for the detection of subclinical keratoconus was more limited (ORA: cutoff 1.17 D, sensitivity 60.0 %, specificity 84.2 %; TD: cutoff 1.29 D, sensitivity 80.0 %, specificity 80.2 %). The vector parameters ORA and TD are able to discriminate with good levels of precision between keratoconus and healthy corneas. For the detection of subclinical keratoconus, only TD seems to be valid.

  15. Computation of astigmatic and trefoil figure errors and misalignments for two-mirror telescopes using nodal-aberration theory.

    PubMed

    Ju, Guohao; Yan, Changxiang; Gu, Zhiyuan; Ma, Hongcai

    2016-05-01

    In active optics systems, one concern is how to quantitatively separate the effects of astigmatic and trefoil figure errors and misalignments that couple together in determining the total aberration fields when wavefront measurements are available at only a few field points. In this paper, we first quantitatively describe the impact of mount-induced trefoil deformation on the net aberration fields by proposing a modified theoretical formulation for the field-dependent aberration behavior of freeform surfaces based on the framework of nodal aberration theory. This formulation explicitly expresses the quantitative relationships between the magnitude of freeform surfaces and the induced aberration components where the freeform surfaces can be located away from the aperture stop and decentered from the optical axis. On this basis, and in combination with the mathematical presentation of nodal aberration theory for the effects of misalignments, we present the analytic expressions for the aberration fields of two-mirror telescopes in the presence of astigmatic primary mirror figure errors, mount-induced trefoil deformations on both mirrors, and misalignments. We quantitatively separate these effects using the analytical expressions with wavefront measurements at a few field points and pointing errors. Valuable insights are provided on how to separate these coupled effects in the computation process. Monte Carlo simulations are conducted to demonstrate the correctness and accuracy of the analytic method presented in this paper.

  16. Laser-assisted In Situ Keratomileusis for Correction of Astigmatism and Increasing Contact Lens Tolerance after Penetrating Keratoplasty

    PubMed Central

    Park, Chang-Hyun; Kim, Su-Young

    2014-01-01

    Purpose To determine effectiveness of laser-assisted in situ keratomileusis (LASIK) in the treatment of astigmatism following penetrating keratoplasty (PK). Methods We performed a retrospective review of medical records of patients who underwent LASIK following PK and had over 1 year of follow-up data. Results Twenty-six patients (26 pairs of eyes) underwent LASIK following PK. Mean age of the patients at the time of LASIK was 40.7 years (range, 26 to 72 years). Following LASIK, the mean cylinder was reduced by 2.4 diopters and mean reduction of cylinder after LASIK was 65.4% from the preoperative values at the last follow-up visit. Uncorrected visual acuity became 20 / 50 or better in 69.2% of the eyes after LASIK. Best-corrected visual acuity became 20 / 50 or better in 73.1% of the eyes after LASIK. All of them were intolerable to contact lenses before LASIK. After LASIK, 6 pairs (23.1%) did not need to use contact lenses and 18 pairs (69.2%) were tolerable to using contact lenses or spectacles. There were no significant endothelial cell density changes 12 months after LASIK (p = 0.239). Conclusions LASIK is effective in the treatment of astigmatism following PK and increases contact lens and spectacle tolerance. PMID:25276076

  17. Apparatus for and method of correcting for astigmatism in a light beam reflected off of a light reflecting surface

    SciTech Connect

    Sawicki, R.H.; Sweatt, W.

    1987-03-03

    An apparatus is described for correcting for astigmatism in a light beam reflected off of a light reflecting surface, comprising: (a) a first means defining a flat, rectangular light reflecting surface which is resiliently bendable, to a limited extent, into different concave and/or convex cylindrical curvatures about a particular axis. The first means is configured so that the light reflecting surface can be adjustably bent into the selected cylindrical curvature by applying a particular bending moment to the first means with respect to the surface, depending upon the curvature desired. The first means includes an integrally formed body member having a main plate-like segment including a front fact defining the light reflecting surface and a pair of spaced-apart flange segments extending rearwardly of the main segment; and (b) second means acting on the first means for adjustably bending the light reflecting surface into a particular selected one of the different cylindrical curvatures, depending upon the astigmatism to be corrected for.

  18. Comparative assessment of astigmatism-corrected Czerny-Turner imaging spectrometer using off-the-shelf optics

    NASA Astrophysics Data System (ADS)

    Yuan, Qun; Zhu, Dan; Chen, Yueyang; Guo, Zhenyan; Zuo, Chao; Gao, Zhishan

    2017-04-01

    We present the optical design of a Czerny-Turner imaging spectrometer for which astigmatism is corrected using off-the-shelf optics resulting in spectral resolution of 0.1 nm. The classic Czerny-Turner imaging spectrometer, consisting of a plane grating, two spherical mirrors, and a sensor with 10-μm pixels, was used as the benchmark. We comparatively assessed three configurations of the spectrometer that corrected astigmatism with divergent illumination of the grating, by adding a cylindrical lens, or by adding a cylindrical mirror. When configured with the added cylindrical lens, the imaging spectrometer with a point field of view (FOV) and a linear sensor achieved diffraction-limited performance over a broadband width of 400 nm centered at 800 nm, while the maximum allowable bandwidth was only 200 nm for the other two configurations. When configured with the added cylindrical mirror, the imaging spectrometer with a one-dimensional field of view (1D FOV) and an area sensor showed its superiority on imaging quality, spectral nonlinearity, as well as keystone over 100 nm bandwidth and 10 mm spatial extent along the entrance slit.

  19. Analytic method for the construction of the fundamental mode of a resonator in the form of a Gaussian beam with complex astigmatism

    SciTech Connect

    Plachenov, A B; Kudashov, V N; Radin, A M

    2007-03-31

    Explicit formulas are obtained for a resonator with the fundamental mode in the form of a Gaussian beam with complex astigmatism. The formulas describe the parameters of the beam directly in terms of the ray matrix without using the procedure of finding its eigenvectors. An example is considered. (resonators. modes)

  20. Changes in astigmatism and corneal higher-order aberrations after phacoemulsification with toric intraocular lens implantation for mild keratoconus with cataract.

    PubMed

    Kamiya, Kazutaka; Shimizu, Kimiya; Miyake, Toshiyuki

    2016-07-01

    To assess the changes in astigmatism and higher-order aberrations (HOAs) after toric intraocular lens (IOL) implantation for mild non-progressive keratoconus with cataract. We prospectively examined 19 eyes of 19 consecutive keratoconic patients (mean age ± standard deviation, 63.1 ± 9.1 years) who underwent phacoemulsification with toric IOL implantation. We determined uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refractive astigmatism, corneal astigmatism, corneal HOAs and astigmatic axis rotation both preoperatively and 3 months postoperatively. Logarithm of the minimal angle of resolution (logMAR) UDVA was significantly improved from 1.14 ± 0.50 preoperatively to 0.46 ± 0.33 postoperatively (Wilcoxon signed-rank test, p < 0.001). LogMAR CDVA was also significantly improved from 0.27 ± 0.45 preoperatively to -0.01 ± 0.09 postoperatively (p < 0.001). In 5 of 6 eyes in which the target refraction was emmetropia, postoperative UDVA was better than 20/32. The achieved spherical equivalent correction was within ±0.5 diopters (D) of the targeted correction in 13 (68 %) eyes and 1.0 in 18 (95 %) eyes. The refractive astigmatism was significantly decreased from -1.92 ± 1.73 D preoperatively to -0.70 ± 0.60 D postoperatively (p = 0.006). The corneal astigmatism changed from 2.89 ± 1.30 D preoperatively to 2.98 ± 1.09 D postoperatively (p = 0.492), which was not statistically significant. The corneal HOAs for a 4-mm pupil was changed from 0.47 ± 0.23 µm preoperatively to 0.52 ± 0.26 µm postoperatively (p = 0.211), which was not statistically significant. According to our experience, toric IOL implantation for mild keratoconic patients having rigid gas-permeable lens intolerance appears to be effective for reducing refractive astigmatism without a significant induction of corneal HOAs.

  1. Comparison of the predictability of refractive cylinder correction by laser in situ keratomileusis in eyes with low or high ocular residual astigmatism.

    PubMed

    Archer, Timothy J; Reinstein, Dan Z; Piñero, David P; Gobbe, Marine; Carp, Glenn I

    2015-07-01

    To compare the manifest refractive cylinder (MRC) predictability of myopic astigmatism laser in situ keratomileusis (LASIK) between eyes with low and high ocular residual astigmatism (ORA). London Vision Clinic, London, United Kingdom. Retrospective case study. The ORA was considered the vector difference between the MRC and the corneal astigmatism. The index of success (IoS), difference vector ÷ MRC, was analyzed for different groups as follows: stage 1, low ORA (ORA ÷ MRC <1), high ORA (ORA ÷ MRC ≥1); stage 2, low ORA group reduced to match the high ORA group for MRC; stage 3, grouped by ORA magnitude with low ORA (<0.50 diopters [D]), mid ORA (0.50 to 1.24 D), and high ORA (≥1.25 D); stage 4, high ORA group subdivided into low (<0.75 D) and high (≥0.75 D) corneal astigmatism. For stage 1, the mean preoperative MRC and mean IoS were -1.32 D ± 0.65 (SD) (range -0.55 to -3.77 D) and 0.27, respectively, for low ORA and -0.79 ± 0.20 D (range -0.56 to -2.05 D) and 0.37, respectively, for high ORA. For stage 2, the mean IoS increased to 0.32 for low ORA. For stage 3, the mean IoS was 0.28, 0.29, and 0.31 for low ORA, mid ORA, and high ORA, respectively. For stage 4, the mean IoS was 0.20 for high ORA/low corneal astigmatism and 0.35 for high ORA/high corneal astigmatism. The MRC predictability was slightly worse in eyes with high ORA when grouped by the ORA ÷ MRC. Matching for the MRC and grouping by ORA magnitude resulted in similar predictability; however, eyes with high ORA and high corneal astigmatism were less predictable. Dr. Reinstein is a consultant to Carl Zeiss Meditec AG, has a proprietary interest in the Artemis technology (Arcscan, Inc.), and is an author of patents related to very-high-frequency digital ultrasound administered by the Center for Technology Licensing at Cornell University, Ithaca, New York, USA. No other author has a financial or proprietary interest in any material or method mentioned. Copyright © 2015 ASCRS and ESCRS

  2. Comparison of Visian toric collamer lens and toric acrylic intraocular lens implantation for the treatment of myopia with astigmatism

    PubMed Central

    Ammar, Hatem; Anbar, Mohamed; Abdellah, Marwa M

    2017-01-01

    Purpose To compare the efficacy and outcome of phakic toric implantable collamer lens (TICL) and refractive clear lens extraction with AcrySof Toric intraocular lens (TIOL) implantation for the treatment of myopic astigmatism. Patients and methods This study assessed eyes with myopic astigmatism >−1 D and ≤−4 D with a spherical equivalent >10 D or <10 D if the patients were unsuitable for corneal refractive surgery. These eyes were divided into group A, in which Visian Toric ICL™ Phakic TICL was implanted, and group B, which involved clear lens extraction with implantation of an AcrySof IQ toric SN60T3-9™ IOL. The outcome and complications were evaluated. Results This study enrolled 63 eyes of 38 patients with a follow-up period of at least 6 months. The mean postoperative spherical equivalent was −0.19±0.31 D in group A and −0.21±0.28 D in group B (P=0.69). The mean postoperative cylinder value was −0.46±0.53 D in group A and −0.32±0.41 D in group B (P=0.35). Postoperative cylinder was <1 D in 76.47% and 79.31% of eyes in groups A and B, respectively. The mean endothelial cell count was reduced by 4.32% in group A and by 5.32% in group B (P=0.003). The mean postoperative intraocular pressure increased insignificantly in group A (P=0.22) and reduced significantly in group B (P=0.004). The complication rate was 11.76% in group A and 6.90% in group B. Conclusion Both procedures showed predictable results and good visual results. However, the loss of accommodation and risk of retinal complications in the TIOL group suggest that the use of TICL for myopic astigmatism is a better choice in younger patients. PMID:28096654

  3. Clinical evaluation of surgery-induced astigmatism in cataract surgery using 2.2 mm or 1.8 mm clear corneal micro-incisions

    PubMed Central

    Yang, Jun; Wang, Xiu; Zhang, Hong; Pang, Yi; Wei, Rui-Hua

    2017-01-01

    AIM To evaluate corneal astigmatism after phacoemulsification using 2.2 mm or 1.8 mm clear corneal micro-incisions and its effects on visual function. METHODS Sixty cases (60 eyes) with cataract were randomly divided into groups A (n=30) and B (n=30) respectively underwent 2.2 mm and 1.8 mm clear corneal tunnel incision phacoemulsification combined with folding intraocular lens implantation from the time direction of 11:00. On day 1 and at 1, 4, and 6wk after operation, patients' vision was measured and both the corneal curvature and corneal thickness (CT) were recorded using Pentacam. RESULTS The measured surgery-induced astigmatism (SIA) in both groups A and B peaked on day 1 after operation, and then gradually decreased and eventually stabilized in week 4. No statistically significant difference was found in corneal astigmatism between two groups (P>0.05). The measured corneal astigmatism at 4wk and 6wk postoperatively were 0.28±0.09 D and 0.27±0.10 D for groups A and 0.27±0.09 D and 0.25±0.10 D for groups B without statistically significant difference (P>0.05). In addition, no significant differences in visual acuity and CT were found between groups A and B before or after operation. CONCLUSION Both 2.2 mm and 1.8 mm micro-incision cataract surgeries result in relatively small SIA with no difference in visual function and corneal astigmatism between two surgery approaches. Thus, the two types of surgical systems are safe and efficient for cataract treatment, by which satisfactory uncorrected visual acuity can be regained early postoperatively. PMID:28149779

  4. Comparative analysis of the efficacy of astigmatic correction after wavefront-guided and wavefront-optimized LASIK in low and moderate myopic eyes

    PubMed Central

    Khalifa, Mounir A.; Alsahn, Mahmoud F.; Shaheen, Mohamed Shafik; Pinero, David P.

    2017-01-01

    AIM To evaluate and compare the efficacy of the astigmatic correction achieved with laser in situ keratomileusis (LASIK) in eyes with myopic astigmatism using wavefront-guided (WFG) and wavefront-optimized (WFO) ablation profiles. METHODS Prospective study included 221 eyes undergoing LASIK: 99 and 122 eyes with low and moderate myopic astigmatism (low and moderate myopia groups). Two subgroups were differentiated in each group according to the ablation profile: WFG subgroup, 109 eyes (45/64, low/moderate myopia groups) treated using the Advanced CustomVue platform (Abbott Medical Optics Inc.), and WFO subgroup, 112 eyes (54/58, low/moderate myopia groups) treated using the EX-500 platform (Alcon). Clinical outcomes were evaluated during a 6-month follow-up, including a vector analysis of astigmatic changes. RESULTS Significantly better postoperative uncorrected visual acuity and efficacy index was found in the WFG subgroups of each group (P≤0.041). Postoperative spherical equivalent and cylinder were significantly higher in WFO subgroups (P≤0.003). In moderate myopia group, a higher percentage of eyes with a postoperative cylinder ≤0.25 D was found in the WFG subgroup (90.6% vs 65.5%, P=0.002). In low and moderate myopia groups, the difference vector was significantly higher in the WFO subgroup compared to WFG (P<0.001). In moderate myopia group, the magnitude (P=0.008) and angle of error (P<0.001) were also significantly higher in the WFO subgroup. Significantly less induction of high order aberrations were found with WFG treatments in both low and moderate myopia groups (P≤0.006). CONCLUSION A more efficacious correction of myopic astigmatism providing a better visual outcome is achieved with WFG LASIK compared to WFO LASIK. PMID:28251090

  5. Comparative evaluation of aspheric toric intraocular lens implantation and limbal relaxing incisions in eyes with cataracts and ≤3 dioptres of astigmatism.

    PubMed

    Lam, Douglas K T; Chow, Vanissa W S; Ye, Cong; Ng, Paul Ka-Fai; Wang, Zheng; Jhanji, Vishal

    2016-02-01

    To compare the visual outcomes of aspheric toric intraocular lens (IOL) implantation and limbal relaxing incisions (LRI) for management of coexisting age-related cataracts and astigmatism. In this prospective study, sixty eyes of 60 patients with visually significant cataract and coexisting corneal astigmatism ≤3 dioptres (D) were randomised to undergo phacoemulsification with either aspheric toric IOL or aspheric monofocal IOL with LRI. The main outcome measures were postoperative 3-month uncorrected visual acuity (UCVA), contrast sensitivity, rotational stability of the toric IOL and spectacle independence. The postoperative UCVA, contrast sensitivity and refractive astigmatism were significantly better than the baseline measurements for both groups (p≤0.001). There was no significant difference detected for these parameters between LRI and toric IOL groups postoperatively (p≥0.119). At both postoperative month 1 and 3, the percentages of eyes in need of spectacles were lower in toric group than LRI group (p≤0.030). IOL misalignment was noted in three eyes in the toric IOL group (mean misalignment 7.67±4.04°). On vector analysis, magnitude of error (ME) was negative in the LRI group indicating undercorrection, whereas the ME was close to zero for toric group. Both toric IOL implantation and LRI were effective in correcting corneal astigmatism ≤3 D during phacoemulsification, while LRI tended to undercorrect astigmatism. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

  6. Methods for calculating the vergence of an astigmatic ray bundle in an optical system that contains a freeform surface

    NASA Astrophysics Data System (ADS)

    Shirayanagi, Moriyasu

    2016-10-01

    A method using the generalized Coddington equations enables calculating the vergence of an astigmatic ray bundle in the vicinity of a skew ray in an optical system containing a freeform surface. Because this method requires time-consuming calculations, however, there is still room for increasing the calculation speed. In addition, this method cannot be applied to optical systems containing a medium with a gradient index. Therefore, we propose two new calculation methods in this paper. The first method, using differential ray tracing, enables us to shorten computation time by using simpler algorithms than those used by conventional methods. The second method, using proximate rays, employs only the ray data obtained from the rays exiting an optical system. Therefore, this method can be applied to an optical system that contains a medium with a gradient index. We show some sample applications of these methods in the field of ophthalmic optics.

  7. Associations between Anisometropia, Amblyopia, and Reduced Stereoacuity in a School-Aged Population with a High Prevalence of Astigmatism

    PubMed Central

    Miller, Joseph M.; Clifford-Donaldson, Candice E.; Harvey, Erin M.

    2008-01-01

    PURPOSE To describe the relation between magnitude of anisometropia and interocular acuity difference (IAD), stereoacuity (SA), and the presence of amblyopia in school-aged members of a Native American tribe with a high prevalence of astigmatism. METHODS Refractive error (cycloplegic autorefraction confirmed by retinoscopy), best corrected monocular visual acuity (VA; Early Treatment Diabetic Retinopathy Study logMAR charts), and best corrected SA (Randot Preschool Stereoacuity Test) were measured in 4- to 13-year-old Tohono O'odham children (N = 972). Anisometropia was calculated in clinical notation (spherical equivalent and cylinder) and in two forms of vector notation that take into account interocular differences in both axis and cylinder magnitude. RESULTS Astigmatism ≥ 1.00 D was present in one or both eyes of 415 children (42.7%). Significant increases in IAD and presence of amblyopia (IAD ≥ 2 logMAR lines) occurred, with ≥ 1 D of hyperopic anisometropia and ≥2 to 3 D of cylinder anisometropia. Significant decreases in SA occurred with ≥0.5 D of hyperopic, myopic, or cylinder anisometropia. Results for vector notation depended on the analysis used, but also showed disruption of SA at lower values of anisometropia than were associated with increases in IAD and presence of amblyopia. CONCLUSIONS Best corrected IAD and presence of amblyopia are related to amount and type of refractive error difference (hyperopic, myopic, or cylindrical) between eyes. Disruption of best corrected random dot SA occurs with smaller interocular differences than those producing an increase in IAD, suggesting that the development of SA is particularly dependent on similarity of the refractive error between eyes. PMID:18539935

  8. Aspheric Micro-monovision LASIK in Correction of Presbyopia and Myopic Astigmatism: Early Clinical Outcomes in a Chinese Population.

    PubMed

    Zhang, Ting; Sun, Yuan; Weng, Shengbei; Liu, Manli; Zhou, Yugui; Yang, Xiaonan; Stojanovic, Aleksandar; Liu, Quan

    2016-10-01

    To analyze early clinical outcomes of aspheric micro-monovision LASIK for correction of presbyopia and myopia with or without astigmatism. Prospective, non-comparative case series of 80 eyes of 40 patients with a mean age of 43.4 ± 4.9 years (range: 38 to 63 years) treated bilaterally using an aspheric micro-monovision protocol. The target refraction was plano for the distance eye and between -0.75 and -2.25 diopters (D) for the near eye. Visual acuity, ocular aberrations, contrast sensitivity, corneal topography, amplitude of accommodation, binocular sensorial function, and satisfaction score questionnaires were evaluated at 3 months after surgery. Three months after surgery, the mean spherical equivalent (SE) refraction in the distance eye was -0.08 ± 0.27 D, whereas the attempted and achieved SE in the near eye were -1.41 ± 0.28 and -1.32 ± 0.35 D, respectively. Ninety-three percent of eyes were within ±0.50 D of target correction of SE. The uncorrected distance visual acuity (UDVA) after surgery was -0.10 ± 0.06 logMAR (20/15.5), 0.22 ± 0.12 logMAR (20/34), and -0.11 ± 0.06 logMAR (20/15), for distance eyes, near eyes, and binocularly, respectively. Ninety-five percent of patients achieved simultaneously uncorrected distance visual acuity 0.0 logMAR (20/20) or better and uncorrected near visual acuity J2 (20/25) or better. Stability was achieved from 1 week of follow-up. The overall satisfaction score for surgery was 92 ± 6. The aspheric micro-monovision protocol provided a well-tolerated and effective means for treating myopic astigmatism and alleviating presbyopic symptoms simultaneously. [J Refract Surg. 2016;32(10):680-685.]. Copyright 2016, SLACK Incorporated.

  9. Evaluation of the diagnostic ability of vector parameters characterizing the corneal astigmatism and regularity in clinical and subclinical keratoconus.

    PubMed

    Martínez-Abad, Antonio; Piñero, David P; Ruiz-Fortes, Pedro; Artola, Alberto

    2017-04-01

    To evaluate the diagnostic ability of the vector parameters ocular residual astigmatism (ORA), topography disparity (TD) and topographic astigmatism CorT (anterior and total) for the detection of clinical and subclinical keratoconus, and to develop a detection model based on them. This study comprised a total of 61 keratoconus eyes (KC group), 19 eyes with subclinical keratoconus (SKC group) and 100 healthy eyes (control group). In all cases, a complete eye exam was performed including an analysis of the corneal structure with the Sirius system (Costruzione Strumenti Oftalmici, CSO). Likewise, the iASSORT software (ASSORT Pty) was used to calculate in all cases the vector parameters ORA, TD and CorT. Significant differences among groups were found in ORA, TD and CorT (anterior and total) (p<0.001). The diagnostic ability of ORA (cutoff 1.255 D, sensitivity/specificity 82%/92%) and TD (cutoff 1.035 D, sensitivity/specificity 78.5%/86%) for the detection of keratoconus was good, whereas anterior and total CorT showed a poorer diagnostic ability. ORA (cutoff 0.925 D, sensitivity/specificity 63.2%/77%) and TD (cutoff 0.710 D, sensitivity/specificity 74%/68%) showed an acceptable diagnostic ability for the detection of subclinical keratoconus, but anterior and total CorT did not. A detection model for subclinical keratoconus was obtained by logistic regression analysis involving TD, anterior corneal spherical aberration and posterior high order aberrations. The vector parameters ORA and TD are useful for the diagnosis of clinical and subclinical keratoconus. In this last condition, the combination of TD with corneal aberrometric data provides a consistent detection model. Copyright © 2016 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

  10. Analysis of focusing error signals by differential astigmatic method under off-center tracking in the land-groove-type optical disk

    NASA Astrophysics Data System (ADS)

    Shinoda, Masahisa; Nakatani, Hidehiko

    2015-04-01

    We theoretically calculate the behavior of the focusing error signal in the land-groove-type optical disk when the objective lens traverses on out of the radius of the optical disk. The differential astigmatic method is employed instead of the conventional astigmatic method for generating the focusing error signals. The signal behaviors are compared and analyzed in terms of the gain difference of the slope sensitivity of the focusing error signals from the land and the groove. In our calculation, the format of digital versatile disc-random access memory (DVD-RAM) is adopted as the land-groove-type optical disk model, and advantageous conditions for suppressing the gain difference are investigated. The calculation method and results described in this paper will be reflected in the next generation land-groove-type optical disks.

  11. An auto-tuning method for focusing and astigmatism correction in HAADF-STEM, based on the image contrast transfer function.

    PubMed

    Baba, N; Terayama, K; Yoshimizu, T; Ichise, N; Tanaka, N

    2001-01-01

    An auto-tuning method for high-angle annular detector dark field scanning transmission electron microscopy (HAADF-STEM) is proposed which corrects the defocus to the optimum Scherzer focus and compensates the astigmatism. Because the method is based on the image contrast transfer function formulated for the HAADF-STEM, the defocus and the astigmatism are accurately measured from input of two different defocus images. The method is designed to work independent of object function in the linear imaging model by analysing the spectral ratio between two Fourier spectra of their images, which is useful for cases where the spectrum of object function is not uniformly spread out over the reciprocal space. The method was preliminarily tested in a Hitachi HD-2000 STEM, and successful results of the auto-tunings from the viewpoint of verification of the algorithm were obtained using general specimens of Au fine particles and a thin section of a semiconductor device.

  12. Induced Higher-order aberrations after Laser In Situ Keratomileusis (LASIK) Performed with Wavefront-Guided IntraLase Femtosecond Laser in moderate to high Astigmatism.

    PubMed

    Al-Zeraid, Ferial M; Osuagwu, Uchechukwu L

    2016-03-22

    Wavefront-guided Laser-assisted in situ keratomileusis (LASIK) is a widespread and effective surgical treatment for myopia and astigmatic correction but whether it induces higher-order aberrations remains controversial. The study was designed to evaluate the changes in higher-order aberrations after wavefront-guided ablation with IntraLase femtosecond laser in moderate to high astigmatism. Twenty-three eyes of 15 patients with moderate to high astigmatism (mean cylinder, -3.22 ± 0.59 dioptres) aged between 19 and 35 years (mean age, 25.6 ± 4.9 years) were included in this prospective study. Subjects with cylinder ≥ 1.5 and ≤2.75 D were classified as moderate astigmatism while high astigmatism was ≥3.00 D. All patients underwent a femtosecond laser-enabled (150-kHz IntraLase iFS; Abbott Medical Optics Inc) wavefront-guided ablation. Uncorrected (UDVA), corrected (CDVA) distance visual acuity in logMAR, keratometry, central corneal thickness (CCT) and higher-order aberrations (HOAs) over a 6 mm pupil, were assessed before and 6 months, postoperatively. The relationship between postoperative change in HOA and preoperative mean spherical equivalent refraction, mean astigmatism, and postoperative CCT were tested. At the last follow-up, the mean UDVA was increased (P < 0.0001) but CDVA remained unchanged (P = 0.48) and no eyes lost ≥2 lines of CDVA. Mean spherical equivalent refraction was reduced (P < 0.0001) and was within ±0.50 D range in 61% of eyes. The average corneal curvature was flatter by 4 D and CCT was reduced by 83 μm (P < 0.0001, for all), postoperatively. Coma aberrations remained unchanged (P = 0.07) while the change in trefoil (P = 0.047) postoperatively, was not clinically significant. The 4th order HOAs (spherical aberration and secondary astigmatism) and the HOA root mean square (RMS) increased from -0.18 ± 0.07 μm, 0.04 ± 0.03 μm and 0.47 ± 0.11 μm, preoperatively, to 0.33 ± 0

  13. Dynamical measurements of motion behavior of free fluorescent sphere using the wide field temporal focusing microscopy with astigmatism method (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Lien, Chi-Hsiang; Lin, Chun-Yu; Chen, Shean-Jen; Chien, Fan-Ching

    2017-02-01

    A three-dimensional (3D) single fluorescent particle tracking strategy based on temporal focusing multiphoton excitation microscopy (TFMPEM) combined with astigmatism imaging is proposed for delivering nanoscale-level axial information that reveals 3D trajectories of single fluorospheres in the axially-resolved multiphoton excitation volume without z-axis scanning. It provides the dynamical ability by measuring the diffusion coefficient of fluorospheres in glycerol solutions with a position standard deviation of 14 nm and 21 nm in the lateral and axial direction and a frame rate of 100 Hz. Moreover, the optical trapping force based on the TFMPEM is minimized to avoid the interference in the tracing measurements compared to that in the spatial focusing MPE approaches. Therefore, we presented a three dimensional single particle tracking strategy to overcome the limitation of the time resolution of the multiphoton imaging using fast frame rate of TFMPEM, and provide three dimensional locations of multiple particles using an astigmatism method.

  14. Efficacy of Wavefront-guided Photorefractive Keratectomy with Iris Registration for Management of Moderate to High Astigmatism by Advanced Personalized Treatment Nomogram

    PubMed Central

    Mohammadpour, Mehrdad; Hashemi, Hassan; Jabbarvand, Mahmoud; Rahmatnejad, Kamran; Sabet, Fatemeh Alsadat

    2016-01-01

    Purpose: To evaluate the efficacy of photorefractive keratectomy (PRK) using the advanced personalized treatment (APT) nomogram for correction of moderate to high astigmatism. Methods: This prospective interventional case series included 60 consecutive eyes of 30 patients undergoing wavefront-guided PRK (Zyoptix 217 Z100 excimer laser, Bausch & Lomb, Munich, Germany) using the APT nomogram and iris registration for myopic astigmatism. Mitomycin-C was applied intraoperatively in all eyes. Ophthalmic examination was performed preoperatively and 1, 3 and 6 months postoperatively. Results: Preoperatively, mean sphere was -1.68 ± 2.08 diopters (D), mean refractive astigmatism was -3.04 ± 1.05 D and mean spherical equivalent (SE) was -3.12 ± 1.77 D. Six months postoperatively, mean sphere was + 0.60 ± 0.64 D (P < 0.005), mean cylinder was -0.43 ± 0.46 D (P < 0.005) and mean SE was + 0.28 ± 0.48 D (P < 0.005). Hyperopic overcorrection (≥ +1.0 D) occurred in 3 (5%) eyes. Postoperatively, root mean square (RMS) of higher order aberrations (HOAs) was significantly increased (P = 0.041). RMS of spherical aberration (Z [4, 0]) showed no significant change after surgery (P = 0.972). Conclusion: Considering the acceptable residual refractive error, low rate of hyperopic overcorrection, acceptable uncorrected visual acuity, and low risk of postoperative corneal haze, PRK using the APT nomogram with iris registration and mitomycin-C use is a safe and effective modality for treatment of moderate to high astigmatism. PMID:27413491

  15. Refractive astigmatism acts predominantly as a source of high spatial frequency image distortion: the associated lineal distortions can be overcome by using a low pass spatial filter!

    PubMed

    Enoch, J M; Lakshminarayanan, V; Kono, M; Shih, P; Strata, E

    Surprisingly, an important characteristic of astigmatism has been overlooked by ophthalmic and clinical scientists. Apparently, refractive astigmatism is due largely to a form of high spatial frequency image distortion. Characteristic astigmatic image distortion can be minimized or eliminated by using a low-pass spatial filter (here, a ground glass plate was employed for this purpose). The ground glass is placed a short distance in front of a visual acuity chart, or it may be used with other tests, such as vernier acuity. This test has been performed by us on large numbers of patients and test subjects. A clinician can try this test for himself/herself. Place a +2.00 D.C. (any axis) lens in front of the eye; the usual distortions will be observed. Locate the ground glass plate as described. The usual distortions associated with the conoid of Stürm will not be visible or will be virtually eliminated, although some image blur will remain. This technique has significance, e.g., in visual screening programs in developing nations, or in assessing patients with media disorders prior to ophthalmic surgery.

  16. Comparison of endothelial cell loss and surgically induced astigmatism following conventional extracapsular cataract surgery, manual small-incision surgery and phacoemulsification.

    PubMed

    George, Ronnie; Rupauliha, Pankaj; Sripriya, A V; Rajesh, P S; Vahan, P Vishnu; Praveen, Smita

    2005-10-01

    To compare the surgically induced astigmatism (SIA) and endothelial cell loss following conventional extracapsular cataract surgery (ECCE), manual small-incision cataract surgery (Blumenthal technique)(SICS) and phacoemulsification (PE) with non-foldable intraocular lens implantation. 186 cataractous eyes with nuclear sclerosis grade 3 or less were randomized to undergo ECCE, SICS or PE with intraocular lens (non-foldable) implantation after a detailed pre-operative assessment. Keratometry and specular microscopy were performed pre-operatively and 6 weeks postoperatively. Surgically induced astigmatism was calculated using the rectangular coordinate method (Holladay et al.). Mean endothelial cell loss was similar for all three groups (p = 0.855); ECCE induced a loss of 4.72% (SD: 13.07); SICS 4.21% (SD: 10.29) and PE 5.41% (SD: 10.99). Mean SIA was 1.77D (1.61D) for the ECCE group, 1.17D (0.95D) for the SICS group and 0.77D (0.65D) for the PE group (p = 0.001). The magnitude of the difference between the SICS and the PE group was 0.4D. PE induced less astigmatism than SICS and ECCE in this study but the magnitude of the difference between SICS and PE was small. There was no significant difference in endothelial cell loss between the three groups.

  17. Anti-drift and auto-alignment mechanism for an astigmatic atomic force microscope system based on a digital versatile disk optical head.

    PubMed

    Hwu, E-T; Illers, H; Wang, W-M; Hwang, I-S; Jusko, L; Danzebrink, H-U

    2012-01-01

    In this work, an anti-drift and auto-alignment mechanism is applied to an astigmatic detection system (ADS)-based atomic force microscope (AFM) for drift compensation and cantilever alignment. The optical path of the ADS adopts a commercial digital versatile disc (DVD) optical head using the astigmatic focus error signal. The ADS-based astigmatic AFM is lightweight, compact size, low priced, and easy to use. Furthermore, the optical head is capable of measuring sub-atomic displacements of high-frequency AFM probes with a sub-micron laser spot (~570 nm, FWHM) and a high-working bandwidth (80 MHz). Nevertheless, conventional DVD optical heads suffer from signal drift problems. In a previous setup, signal drifts of even thousands of nanometers had been measured. With the anti-drift and auto-alignment mechanism, the signal drift is compensated by actuating a voice coil motor of the DVD optical head. A nearly zero signal drift was achieved. Additional benefits of this mechanism are automatic cantilever alignment and simplified design.

  18. Genome-wide association study for refractive astigmatism reveals genetic co-determination with spherical equivalent refractive error: the CREAM consortium.

    PubMed

    Li, Qing; Wojciechowski, Robert; Simpson, Claire L; Hysi, Pirro G; Verhoeven, Virginie J M; Ikram, Mohammad Kamran; Höhn, René; Vitart, Veronique; Hewitt, Alex W; Oexle, Konrad; Mäkelä, Kari-Matti; MacGregor, Stuart; Pirastu, Mario; Fan, Qiao; Cheng, Ching-Yu; St Pourcain, Beaté; McMahon, George; Kemp, John P; Northstone, Kate; Rahi, Jugnoo S; Cumberland, Phillippa M; Martin, Nicholas G; Sanfilippo, Paul G; Lu, Yi; Wang, Ya Xing; Hayward, Caroline; Polašek, Ozren; Campbell, Harry; Bencic, Goran; Wright, Alan F; Wedenoja, Juho; Zeller, Tanja; Schillert, Arne; Mirshahi, Alireza; Lackner, Karl; Yip, Shea Ping; Yap, Maurice K H; Ried, Janina S; Gieger, Christian; Murgia, Federico; Wilson, James F; Fleck, Brian; Yazar, Seyhan; Vingerling, Johannes R; Hofman, Albert; Uitterlinden, André; Rivadeneira, Fernando; Amin, Najaf; Karssen, Lennart; Oostra, Ben A; Zhou, Xin; Teo, Yik-Ying; Tai, E Shyong; Vithana, Eranga; Barathi, Veluchamy; Zheng, Yingfeng; Siantar, Rosalynn Grace; Neelam, Kumari; Shin, Youchan; Lam, Janice; Yonova-Doing, Ekaterina; Venturini, Cristina; Hosseini, S Mohsen; Wong, Hoi-Suen; Lehtimäki, Terho; Kähönen, Mika; Raitakari, Olli; Timpson, Nicholas J; Evans, David M; Khor, Chiea-Chuen; Aung, Tin; Young, Terri L; Mitchell, Paul; Klein, Barbara; van Duijn, Cornelia M; Meitinger, Thomas; Jonas, Jost B; Baird, Paul N; Mackey, David A; Wong, Tien Yin; Saw, Seang-Mei; Pärssinen, Olavi; Stambolian, Dwight; Hammond, Christopher J; Klaver, Caroline C W; Williams, Cathy; Paterson, Andrew D; Bailey-Wilson, Joan E; Guggenheim, Jeremy A

    2015-02-01

    To identify genetic variants associated with refractive astigmatism in the general population, meta-analyses of genome-wide association studies were performed for: White Europeans aged at least 25 years (20 cohorts, N = 31,968); Asian subjects aged at least 25 years (7 cohorts, N = 9,295); White Europeans aged <25 years (4 cohorts, N = 5,640); and all independent individuals from the above three samples combined with a sample of Chinese subjects aged <25 years (N = 45,931). Participants were classified as cases with refractive astigmatism if the average cylinder power in their two eyes was at least 1.00 diopter and as controls otherwise. Genome-wide association analysis was carried out for each cohort separately using logistic regression. Meta-analysis was conducted using a fixed effects model. In the older European group the most strongly associated marker was downstream of the neurexin-1 (NRXN1) gene (rs1401327, P = 3.92E-8). No other region reached genome-wide significance, and association signals were lower for the younger European group and Asian group. In the meta-analysis of all cohorts, no marker reached genome-wide significance: The most strongly associated regions were, NRXN1 (rs1401327, P = 2.93E-07), TOX (rs7823467, P = 3.47E-07) and LINC00340 (rs12212674, P = 1.49E-06). For 34 markers identified in prior GWAS for spherical equivalent refractive error, the beta coefficients for genotype versus spherical equivalent, and genotype versus refractive astigmatism, were highly correlated (r = -0.59, P = 2.10E-04). This work revealed no consistent or strong genetic signals for refractive astigmatism; however, the TOX gene region previously identified in GWAS for spherical equivalent refractive error was the second most strongly associated region. Analysis of additional markers provided evidence supporting widespread genetic co-susceptibility for spherical and astigmatic refractive errors.

  19. Hard x-ray spectroscopy and imaging by a reflection zone plate in the presence of astigmatism

    DOE PAGES

    Braig, Christoph; Lochel, Heike; Firsov, Alexander; ...

    2015-12-17

    Here, the feasibility of an off-axis x-ray reflection zone plate to perform wavelength-dispersive spectroscopy, on-axis point focusing, and two-dimensional imaging is demonstrated by means of one and the same diffractive optical element (DOE) at a synchrotron radiation facility. The resolving power varies between 3 × 101 and 4 × 102 in the range of 7.6 keV to 9.0 keV, with its maximum at the design energy of 8.3 keV. This result is verified using an adjustable entrance slit, by which horizontal (H) and vertical (V) focusing to 0.85 μm(H) and 1.29 μm(V) is obtained near the sagittal focal plane ofmore » the astigmatic configuration. An angular and axial scan proves an accessible field of view of at least 0.6 arcmin × 0.8 arcmin and a focal depth of ±0.86 mm. Supported by the grating efficiency of around 17.5% and a very short pulse elongation, future precision x-ray fluorescence and absorption studies of transition metals at their K-edge on an ultrashort timescale could benefit from our findings.« less

  20. Hard x-ray spectroscopy and imaging by a reflection zone plate in the presence of astigmatism

    SciTech Connect

    Braig, Christoph; Lochel, Heike; Firsov, Alexander; Brzhezinskaya, Maria; Hafner, Aljosa; Rehanek, Jens; Wojcik, Michael; Macrander, Albert; Assoufid, Lahsen; Erko, Alexei

    2015-12-17

    Here, the feasibility of an off-axis x-ray reflection zone plate to perform wavelength-dispersive spectroscopy, on-axis point focusing, and two-dimensional imaging is demonstrated by means of one and the same diffractive optical element (DOE) at a synchrotron radiation facility. The resolving power varies between 3 × 101 and 4 × 102 in the range of 7.6 keV to 9.0 keV, with its maximum at the design energy of 8.3 keV. This result is verified using an adjustable entrance slit, by which horizontal (H) and vertical (V) focusing to 0.85 μm(H) and 1.29 μm(V) is obtained near the sagittal focal plane of the astigmatic configuration. An angular and axial scan proves an accessible field of view of at least 0.6 arcmin × 0.8 arcmin and a focal depth of ±0.86 mm. Supported by the grating efficiency of around 17.5% and a very short pulse elongation, future precision x-ray fluorescence and absorption studies of transition metals at their K-edge on an ultrashort timescale could benefit from our findings.

  1. A numerical-experimental protocol to characterize corneal tissue with an application to predict astigmatic keratotomy surgery.

    PubMed

    Ariza-Gracia, M Á; Ortillés, Á; Cristóbal, J Á; Rodríguez Matas, J F; Calvo, B

    2017-10-01

    Tonometers are intended to determine the intraocular pressure (IOP) and the quality of corneal tissue. In contrast to the physiological state of stress of the cornea, tonometers induce non-physiological bending stress. Recently, the use of a single experiment to calibrate a set of corneal mechanical properties was suggested to be an ill-posed problem. Thus, we propose a numerical-experimental protocol that uses inflation and indentation experiments simultaneously, restricting the optimization space to circumvent the ambiguity of the fitting. For the first time, both corneal behaviors, i.e., biaxial tension (physiological) and bending (non-physiological), are taken into account. The experimental protocol was performed using an animal model (New Zealand rabbit's cornea). The patient-specific geometry and IOP were registered using a MODI topographer (CSO, Italy) and an applanation tonometer, respectively. The mechanical response was evaluated using inflation and indentation experiments. Subsequently, the optimal set of material properties is identified via an inverse finite element method. To validate the methodology, an in vivo incisional refractive surgery (astigmatic keratotomy, AK) is performed on four animals. The optical outcomes showed a good agreement between the real and simulated surgeries, indicating that the protocol can provide a reliable set of mechanical properties that enables further applications and simulations. After a reliable ex vivo database of inflation experiments is built, our protocol could be extended to humans. Copyright © 2017 Elsevier Ltd. All rights reserved.

  2. Ultra-high-speed 3D astigmatic particle tracking velocimetry: application to particle-laden supersonic impinging jets

    NASA Astrophysics Data System (ADS)

    Buchmann, N. A.; Cierpka, C.; Kähler, C. J.; Soria, J.

    2014-11-01

    The paper demonstrates ultra-high-speed three-component, three-dimensional (3C3D) velocity measurements of micron-sized particles suspended in a supersonic impinging jet flow. Understanding the dynamics of individual particles in such flows is important for the design of particle impactors for drug delivery or cold gas dynamic spray processing. The underexpanded jet flow is produced via a converging nozzle, and micron-sized particles ( d p = 110 μm) are introduced into the gas flow. The supersonic jet impinges onto a flat surface, and the particle impact velocity and particle impact angle are studied for a range of flow conditions and impingement distances. The imaging system consists of an ultra-high-speed digital camera (Shimadzu HPV-1) capable of recording rates of up to 1 Mfps. Astigmatism particle tracking velocimetry (APTV) is used to measure the 3D particle position (Cierpka et al., Meas Sci Technol 21(045401):13, 2010) by coding the particle depth location in the 2D images by adding a cylindrical lens to the high-speed imaging system. Based on the reconstructed 3D particle positions, the particle trajectories are obtained via a higher-order tracking scheme that takes advantage of the high temporal resolution to increase robustness and accuracy of the measurement. It is shown that the particle velocity and impingement angle are affected by the gas flow in a manner depending on the nozzle pressure ratio and stand-off distance where higher pressure ratios and stand-off distances lead to higher impact velocities and larger impact angles.

  3. LASER BEAMS: Amplitude—phase mode structure of an astigmatic Gaussian beam in ring lasers with a nonplanar four-mirror cavity and an aperture

    NASA Astrophysics Data System (ADS)

    Broslavets, Yu Yu; Zaitseva, T. E.; Kazakov, A. A.; Fomichev, A. A.

    2006-05-01

    The structure of the fundamental mode field in a nonplanar ring four-mirror resonator with an aperture is determined taking into account rotations of the amplitude and phase distributions of an astigmatic Gaussian beam. The rotation angles of the axes of these distributions are calculated upon variations in the characteristic aperture size and the angle of curvature (nonplanarity) of the resonator. The effect of the resonator aperture and nonplanarity on the intensity distribution of the interference pattern behind a mixer is studied. It is shown that interference fringes have a slope depending on the orientations of the amplitude and phase distributions of the mode.

  4. Repeatability and comparability of corneal power and corneal astigmatism obtained from a point-source color light-emitting diode topographer, a Placido-based corneal topographer, and a low-coherence reflectometer.

    PubMed

    Ventura, Bruna V; Al-Mohtaseb, Zaina; Wang, Li; Koch, Douglas D; Weikert, Mitchell P

    2015-10-01

    To assess the repeatability and agreement of corneal power and astigmatism obtained from the Cassini point-source color light-emitting diode (LED) topographer, Humphrey Atlas 9000 Placido-based corneal topographer, and Lenstar LS-900 low-coherence reflectometer in normal eyes. Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Evaluation of diagnostic test or technology. Consecutively enrolled patients with normal corneas were enrolled. Three sets of measurements were obtained using the color-LED topographer, the Placido topographer, and the reflectometer. Vector analysis was used in the astigmatism analysis. The repeatability was evaluated using the within-subject standard deviation, coefficient of variation (CoV), and intraclass correlation coefficient (ICC). Agreement was verified using Bland-Altman plots. The paired Student t test was used to assess statistical significance. Thirty-two eyes (32 patients) were evaluated. All devices provided highly repeatable corneal power and astigmatism measurements (ICC > 0.9) except for the Placido topographer with regard to J45 (ICC = 0.721). The color-LED topographer and the reflectometer obtained similar mean values of corneal power, astigmatism magnitude, J0, and J45 (P > .05), which was also true when comparing the color-LED topographer and the Placido topographer, except for the mean corneal power (P = .0007). The Bland-Altman plots showed a wide data spread for all analyzed variables. The color-LED topographer provided highly repeatable corneal power and astigmatism measurements. Even though it obtained values similar to those of the reflectometer and the Placido topographer, the wide data spread discourages their interchangeable use to assess corneal power and astigmatism. Drs. Wang, Koch, and Weikert are consultants to Ziemer USA, Inc. Dr. Koch is a consultant to Abbott Medical Optics, Inc., Alcon Surgical, Inc., and i-Optics, Corp. Drs. Ventura and Al-Mohtaseb have no financial or proprietary

  5. Artisan iris-fixated toric phakic and aphakic intraocular lens implantation for the correction of astigmatic refractive error after radial keratotomy.

    PubMed

    Tahzib, Nayyirih G; Eggink, Fred A G J; Odenthal, Monica T P; Nuijts, Rudy M M A

    2007-03-01

    We report 2 patients who had radial keratotomy (RK) to correct myopia. The first patient developed a postoperative hyperopic shift and cataract. Nine years post RK, she had intracapsular cataract extraction and implantation of an Artisan aphakic intraocular lens (IOL). Twenty years post RK, hyperopia and astigmatism progressed to +7.0 -5.75 x 100 with a best corrected visual acuity (BCVA) of 20/20. Due to contact lens intolerance, the Artisan aphakic IOL was exchanged for an Artisan toric aphakic IOL. Three months later, the BCVA was 20/20 with +1.0 -0.50 x 130. The second patient demonstrated residual myopic astigmatism 6 years after bilateral RK and had become contact-lens intolerant. An Artisan toric phakic IOL was implanted in both eyes. Four months later, the BCVA was 20/25 with a refraction of +0.25 -1.0 x 135 and 20/20 with a refraction of -1.0 x 40. Both patients were satisfied with the visual outcomes.

  6. Mini-incision cataract surgery and toric lens implantation for the reduction of high myopic astigmatism in patients with pellucid marginal degeneration

    PubMed Central

    Balestrazzi, A; Baiocchi, S; Balestrazzi, A; Cartocci, G; Tosi, G M; Martone, G; Michieletto, P

    2015-01-01

    Purpose To evaluate the clinical outcomes, safety, and efficacy of cataract surgery with the implantation of a toric intraocular lens (IOL) in eyes with stable pellucid marginal degeneration (PMD). Methods Eleven eyes (eight patients) diagnosed as stable PMD and cataract underwent mini-incision 2.2 mm cataract surgery followed by the implantation of hydrophobic toric aspheric IOL (AcrySof IQ Toric IOL, Alcon, Fort Worth, TX, USA). Perioperative variables of interest included uncorrected (UDVA) and corrected (CDVA) distance visual acuities, manifest refraction, and corneal topography. Paired samples t-tests were used to analyze preoperative and postoperative visual acuity, astigmatism, and spherical equivalent (SE) parameters. Follow-up was 6 months. Results The mean CDVA was 0.62±0.26 logMAR preoperatively and 0.07±0.07 logMAR postoperatively. The mean preoperative sphere and cylinder was −3.14±3.58D and −4.84±2.02D, respectively. The mean postoperative manifest refractive sphere and cylinder was −0.30±0.51D and −0.81±1.51D, respectively. There was a significant reduction in refractive astigmatism after toric IOL implantation (P<0.002). The toric IOL axis rotation was <5° in all cases at the final follow-up. Conclusions Implantation of hydrophobic toric IOL was a safe and effective surgical procedure to correct mild to moderate stable PMD. PMID:25721517

  7. Facts about Astigmatism

    MedlinePlus

    ... visual function, preservation of sight, and the special health problems and requirements of the blind.” News & Events Events Calendar NEI Press Releases News from NEI Grantees Spokesperson bios Statistics and ... Frequently asked questions Clinical Studies Publications Catalog ...

  8. Simultaneous three-dimensional temperature and velocity field measurements using astigmatic imaging of non-encapsulated thermo-liquid crystal (TLC) particles.

    PubMed

    Segura, Rodrigo; Rossi, Massimiliano; Cierpka, Christian; Kähler, Christian J

    2015-02-07

    A combination of cutting edge developments is presented to characterize three-dimensional (3D) temperature and velocity fields in microscopic flows. An emulsion of non-encapsulated thermo-liquid crystal (TLC) micro spheres, with a narrow size distribution is used to track the flow's motion and temperature distribution. A state-of-the-art light engine, which combines the spectrum of six light pipes, provides a balanced illumination which allows for strong and detectable color patterns across the TLC's temperature response range. Lastly, the ability of the TLC material to reflect select wavelength bands with an unchanging and independent circular polarization chirality is exploited by a filter that blocks background noise, while exclusively transmitting the color signal of the TLC particles. This approach takes advantage of the peculiar physical properties of TLCs to allow the estimation of individual TLC particle's 3D position, for the first time, using Astigmatism Particle Tracking Velocimetry (APTV).

  9. Reconstruction of an astigmatic hard X-ray beam and alignment of K-B mirrors from ptychographic coherent diffraction data.

    PubMed

    Kewish, Cameron M; Guizar-Sicairos, Manuel; Liu, Chian; Qian, Jun; Shi, Bing; Benson, Christa; Khounsary, Ali M; Vila-Comamala, Joan; Bunk, Oliver; Fienup, James R; Macrander, Albert T; Assoufid, Lahsen

    2010-10-25

    We have used coherent X-ray diffraction experiments to characterize both the 1-D and 2-D foci produced by nanofocusing Kirkpatrick-Baez (K-B) mirrors, and we find agreement. Algorithms related to ptychography were used to obtain a 3-D reconstruction of a focused hard X-ray beam waist, using data measured when the mirrors were not optimally aligned. Considerable astigmatism was evident in the reconstructed complex wavefield. Comparing the reconstructed wavefield for a single mirror with a geometrical projection of the wavefront errors expected from optical metrology data allowed us to diagnose a 40 μrad misalignment in the incident angle of the first mirror, which had occurred during the experiment. Good agreement between the reconstructed wavefront obtained from the X-ray data and off-line metrology data obtained with visible light demonstrates the usefulness of the technique as a metrology and alignment tool for nanofocusing X-ray optics.

  10. Academic and Workplace-related Visual Stresses Induce Detectable Deterioration Of Performance, Measured By Basketball Trajectories and Astigmatism Impacting Athletes Or Students In Military Pilot Training.

    NASA Astrophysics Data System (ADS)

    Mc Leod, Roger D.

    2004-03-01

    Separate military establishments across the globe can confirm that a high percentage of their prospective pilots-in-training are no longer visually fit to continue the flight training portion of their programs once their academic coursework is completed. I maintain that the visual stress induced by those intensive protocols can damage the visual feedback mechanism of any healthy and dynamic system beyond its usual and ordinary ability to self-correct minor visual loss of acuity. This deficiency seems to be detectable among collegiate and university athletes by direct observation of the height of the trajectory arc of a basketball's flight. As a particular athlete becomes increasingly stressed by academic constraints requiring long periods of concentrated reading under highly static angular convergence of the eyes, along with unfavorable illumination and viewing conditions, eyesight does deteriorate. I maintain that induced astigmatism is a primary culprit because of the evidence of that basketball's trajectory! See the next papers!

  11. Analysis of behavior of focusing error signals generated by astigmatic method when a focused spot moves beyond the radius of a land-groove-type optical disk

    NASA Astrophysics Data System (ADS)

    Shinoda, Masahisa; Nakatani, Hidehiko; Nakai, Kenya; Ohmaki, Masayuki

    2015-09-01

    We theoretically calculate behaviors of focusing error signals generated by an astigmatic method in a land-groove-type optical disk. The focusing error signal from the land does not coincide with that from the groove. This behavior is enhanced when a focused spot of an optical pickup moves beyond the radius of the optical disk. A gain difference between the slope sensitivities of focusing error signals from the land and the groove is an important factor with respect to stable focusing servo control. In our calculation, the format of digital versatile disc-random access memory (DVD-RAM) is adopted as the land-groove-type optical disk model, and the dependences of the gain difference on various factors are investigated. The gain difference strongly depends on the optical intensity distribution of the laser beam in the optical pickup. The calculation method and results in this paper will be reflected in newly developed land-groove-type optical disks.

  12. Clinical outcomes of posterior chamber toric phakic intraocular lens implantation for the correction of high myopic astigmatism in eyes with keratoconus: 6-month follow-up.

    PubMed

    Kamiya, Kazutaka; Shimizu, Kimiya; Kobashi, Hidenaga; Komatsu, Mari; Nakamura, Akio; Nakamura, Tomoaki; Ichikawa, Kazuo

    2011-07-01

    To assess the early clinical outcomes of toric implantable collamer lenses (toric ICL™, STAAR Surgical) for the correction of high myopic astigmatism with keratoconus. This study evaluated 27 eyes of 14 patients with spherical equivalents of -10.11 ± 2.46 D (mean ± standard deviation) and astigmatism of -3.03 ± 1.58 D who underwent toric ICL implantation for mild keratoconus. Before, and 1, 3 and 6 months after surgery, we assessed the safety, efficacy, predictability, stability, and adverse events of the surgery. LogMAR uncorrected visual acuity (UCVA) and LogMAR best spectacle-corrected visual acuity (BSCVA) were -0.09 ± 0.16 and -0.15 ± 0.09 respectively, 6 months after surgery. The safety and efficacy indices were 1.12 ± 0.18 and 1.01 ± 0.25. At 6 months, 85% and 96% of the eyes were within ±0.5 and ±1.0 D respectively of the targeted correction. Manifest refraction changes of 0.00 ± 0.35 D occurred from 1 week to 6 months. No vision-threatening complications occurred during the observation period. Toric ICL implantation was good in all measures of safety, efficacy, predictability, and stability for the correction of spherical and cylindrical errors in eyes with early keratoconus throughout the 6-month follow-up period, suggesting its viability as a surgical option for the treatment of such eyes.

  13. Refinement of Intraocular Pressure Measurements made by Ocular Response Analyzer following Laser in Situ Keratomileusis using M2 90 Moria Microkeratome for Egyptian Myopic and Astigmatic Patients

    PubMed Central

    Refai, Tamer Adel; Hassanin, Olfat A.

    2016-01-01

    Introduction The Goldmann applanation tonometer readings were noted to be markedly reduced after Lasik surgery using a thin flap technique which is widely used nowadays, to correct a wide range of myopia and astigmatism. The Ocular Response Analyzer (ORA) is considered one of the important tools for refinement of Intraocular Pressure (IOP) measurements. The aim of this study is to evaluate and refine ORA measurements for IOP changes post- M2 90 Moria microkeratome Lasik procedure for Egyptian myopic and astigmatic patients trying to aid in glaucoma diagnosis and management. Methods Thirty-five eyes of nineteen Egyptian patients with myopia or myopic astigmatism who had undergone Lasik procedure using M2 90 Moria microkeratome were included in this consecutive case series study. All cases were subjected to full ophthalmological examination including uncorrected and best corrected visual acuity, refraction, slit lamp examination, Scheimpflug imaging and ORA (Reichert Ophthalmic Instruments, Inc., Buffalo, NY, USA). The refractive errors were measured using an auto refractometer and were confirmed by trial. For the ocular response analyzer, the Goldmann-correlated IOP measurement (IOPg) which simulates IOP measured by Goldmann tonometer and the Corneal-Compensated Intraocular Pressure (IOPcc) that takes corneal biomechanical properties into consideration were reported as well as the Corneal Hysteresis (CH) and the Corneal Resistance Factor (CRF). Cases were examined preoperatively and again about one month after Lasik, after stabilization of eye condition. The collected data were tabulated and analysed with the suitable statistical methods. The mean values and standard deviation were calculated for quantitative data. Comparison tests (t-test) and correlation tests (Pearson) were also performed. Results In our study, involving M2 90 Moria microkeratome Lasik procedure, a highly significant post-Lasik reduction in IOPg (t-test = 8.62 (p<0.01), and a statistically

  14. Photorefractive keratectomy for myopia and myopic astigmatism correction using the WaveLight Allegretto Wave Eye-Q excimer laser system.

    PubMed

    Costa, Esmeralda; Franqueira, Nuno; Rosa, Andreia M; Tavares, Cristina; Quadrado, Maria J; Lobo, Conceição; Murta, Joaquim N

    2014-06-01

    To analyze photorefractive keratectomy (PRK) outcomes in myopia and myopic astigmatism correction using the WaveLight Allegretto Wave Eye-Q(®) excimer laser system (WaveLight Laser Technologie AG, Erlangen, Germany). 222 eyes of 151 patients underwent PRK (mean age 33.5 ± 6.8 years). Pre-operative best spectacle-corrected visual acuity (BSCVA) ranged from 0.4 to -0.1 logMAR (mean -0.03 ± 0.06). Mean spherical equivalent (SE) was -3.29 ± 1.20 D. Efficacy, predictability and safety were evaluated. Minimum follow-up was 3 months. Accountability at 3 and 6 months was 100 and 54 %, respectively (median follow-up 5 months, mean 5.2 ± 2.6 months). At 3 months, mean uncorrected visual acuity (UCVA) was -0.02 ± 0.07 logMAR, BSCVA -0.03 ± 0.05 logMAR, efficacy index 0.98 and safety index 1.02. UCVA was ≥20/16 in 40.1 %, ≥20/20 in 86.5 % and ≥20/25 in 98.2 %. Mean SE was -0.02 ± 0.20 D. Residual refractive error was ± 0.13 D in 81.5 %, ± 0.25 D in 88.7 % and ± 0.50 D in 97.7 %. At 6 months, outcomes were similar: mean UCVA was -0.02 ± 0.07 logMAR, BSCVA -0.03 ± 0.06 logMAR, efficacy index 1.00 and safety index 1.03. UCVA was ≥20/16 in 43.7 %, ≥20/20 in 86.6 % and ≥20/25 in 96.6 %. Mean SE was -0.02 ± 0.17 D. Residual refractive error was ± 0.13 D in 86.6 %, ± 0.25 D in 93.3 % and ± 0.50 D in 98.3 %. Refractive stability was achieved at 3 months. No patient lost more than one line of BSCVA. There were no retreatments. The WaveLight Allegretto Wave Eye-Q is effective, predictable and safe in low-to-moderate myopia and myopic astigmatism PRK correction.

  15. Comparison of surgically induced astigmatism after coaxial phacoemulsification through 1.8 mm microincision and bimanual phacoemulsification through 1.7 mm microincision.

    PubMed

    Wilczynski, Michal; Supady, Ewa; Piotr, Loba; Synder, Aleksandra; Palenga-Pydyn, Dorota; Omulecki, Wojciech

    2009-09-01

    To compare surgically induced astigmatism (SIA) after coaxial 1.8 mm microincision cataract surgery (MICS) and bimanual 1.7 mm MICS calculated with 3 mathematical methods. Department of Ophthalmology, Medical University of Lodz, Lodz, Poland. Study comprised a nonrandomized prospective consecutive series of 58 eyes of 58 patients who had uneventful coaxial MICS with implantation of an Akreos MI60 foldable intraocular lens (IOL) using a 1.8 mm temporal clear corneal incision. Fifty eyes of 50 patients who had uneventful bimanual MICS through a 1.7 mm clear corneal incision for a sleeveless phaco tip and a 1.5 mm side port for an irrigating chopper with implantation of an Acri.Smart 48S foldable IOL served as a comparison group. All surgery was performed by 2 experienced surgeons. Surgically induced astigmatism was calculated using 3 methods. The patients were examined preoperatively and 2 weeks to 1 month postoperatively. No intraoperative or postoperative complications were seen in any patient. The corrected distance visual acuity improved significantly in both groups after surgery (P<.01); the visual outcomes were not significantly different (P>.05). In vector analysis, the mean SIA was 0.42 +/- 0.29 in the coaxial MICS group and 0.50 +/- 0.24 in the bimanual group; the difference was not statistically significant (P>.05). In vector decomposition, the mean SIA (C90) coaxial MICS group was 0.23 +/- 0.29 in the coaxial MICS group and 0.23 +/- 0.22 in the bimanual MICS group; the difference was not significant. Using the Naeser method, DeltaKP-90 was calculated, amounting to 0.05 +/- 0.44 in the coaxial MICS group and -0.04 +/- 0.42 in the bimanual MICS group; the difference was not significant. The amount of SIA induced by bimanual MICS and coaxial MICS phacoemulsification was very small. The bimanual MICS induced a slightly higher degree of SIA; however, according to all methods of SIA analysis, there was no significant difference in the mean SIA induced by both

  16. Neck/shoulder discomfort due to visually demanding experimental near work is influenced by previous neck pain, task duration, astigmatism, internal eye discomfort and accommodation

    PubMed Central

    Forsman, Mikael; Richter, Hans O.

    2017-01-01

    Visually demanding near work can cause eye discomfort, and eye and neck/shoulder discomfort during, e.g., computer work are associated. To investigate direct effects of experimental near work on eye and neck/shoulder discomfort, 33 individuals with chronic neck pain and 33 healthy control subjects performed a visual task four times using four different trial lenses (referred to as four different viewing conditions), and they rated eye and neck/shoulder discomfort at baseline and after each task. Since symptoms of eye discomfort may differ depending on the underlying cause, two categories were used; internal eye discomfort, such as ache and strain, that may be caused by accommodative or vergence stress; and external eye discomfort, such as burning and smarting, that may be caused by dry-eye disorders. The cumulative performance time (reflected in the temporal order of the tasks), astigmatism, accommodation response and concurrent symptoms of internal eye discomfort all aggravated neck/shoulder discomfort, but there was no significant effect of external eye discomfort. There was also an interaction effect between the temporal order and internal eye discomfort: participants with a greater mean increase in internal eye discomfort also developed more neck/shoulder discomfort with time. Since moderate musculoskeletal symptoms are a risk factor for more severe symptoms, it is important to ensure a good visual environment in occupations involving visually demanding near work. PMID:28832612

  17. Wavefront-Guided Photorefractive Keratectomy with the Use of a New Hartmann-Shack Aberrometer in Patients with Myopia and Compound Myopic Astigmatism

    PubMed Central

    Schallhorn, Steven C.; Venter, Jan A.; Hannan, Stephen J.; Hettinger, Keith A.

    2015-01-01

    Purpose. To assess refractive and visual outcomes and patient satisfaction of wavefront-guided photorefractive keratectomy (PRK) in eyes with myopia and compound myopic astigmatism, with the ablation profile derived from a new Hartmann-Shack aberrometer. Methods. In this retrospective study, 662 eyes that underwent wavefront-guided PRK with a treatment profile derived from a new generation Hartmann-Shack aberrometer (iDesign aberrometer, Abbott Medical Optics, Inc., Santa Ana, CA) were analyzed. The preoperative manifest sphere ranged from −0.25 to −10.75 D, and preoperative manifest cylinder was between 0.00 and −5.25 D. Refractive and visual outcomes, vector analysis of the change in refractive cylinder, and patient satisfaction were evaluated. Results. At 3 months, 91.1% of eyes had manifest spherical equivalent within 0.50 D. The percentage of eyes achieving uncorrected distance visual acuity 20/20 or better was 89.4% monocularly and 96.5% binocularly. The mean correction ratio of refractive cylinder was 1.02 ± 0.43, and the mean error of angle was 0.00 ± 14.86° at 3 months postoperatively. Self-reported scores for optical side effects, such as starburst, glare, halo, ghosting, and double vision, were low. Conclusion. The use of a new Hartmann-Shack aberrometer for wavefront-guided photorefractive keratectomy resulted in high predictability, efficacy, and patient satisfaction. PMID:26504595

  18. Spatial distribution measurement of atomic radiation with an astigmatism-corrected Czerny-Turner-type spectrometer in the Large Helical Device

    SciTech Connect

    Goto, Motoshi; Morita, Shigeru

    2006-10-15

    Emission lines in the visible/UV wavelength ranges are observed with 80 lines of sight which cover an entire poloidal cross section of the plasma in the Large Helical Device. The emitted light is received with optical fibers having 100 {mu}m diameter and is guided into a 1.33 m Czerny-Turner-type spectrometer based on spherical mirrors for collimating and focusing. A charge-coupled device having 13.3x13.3 mm{sup 2} area size is used as the detector and the spectra from all the lines of sight are recorded perpendicularly to the wavelength dispersion. The spectrometer is equipped with optics located in front of the entrance slit to correct the difference between the meridional and sagittal focal points, and thus the astigmatism, which otherwise causes severe cross talk between adjacent optical fiber images on the detector, is corrected. Consequently, simultaneous spectral measurement with 80 lines of sight is realized. The Zeeman splitting of a neutral helium line, {lambda}667.8 nm (2 {sup 1}P-3 {sup 1}D), which is caused by the magnetic field for plasma confinement, is measured with the spectrometer. Though the obtained line profile is in general a superposition of several components on the same line of sight, they can be separated according to their different splitting widths. The two-dimensional poloidal distribution of the helium line intensity is obtained with the help of a tomographic technique.

  19. Transmissive liquid-crystal device for correcting primary coma aberration and astigmatism in biospecimen in two-photon excitation laser scanning microscopy

    NASA Astrophysics Data System (ADS)

    Tanabe, Ayano; Hibi, Terumasa; Ipponjima, Sari; Matsumoto, Kenji; Yokoyama, Masafumi; Kurihara, Makoto; Hashimoto, Nobuyuki; Nemoto, Tomomi

    2016-12-01

    All aberrations produced inside a biospecimen can degrade the quality of a three-dimensional image in two-photon excitation laser scanning microscopy. Previously, we developed a transmissive liquid-crystal device to correct spherical aberrations that improved the image quality of a fixed-mouse-brain slice treated with an optical clearing reagent. In this study, we developed a transmissive device that corrects primary coma aberration and astigmatism. The motivation for this study is that asymmetric aberration can be induced by the shape of a biospecimen and/or by a complicated refractive-index distribution in a sample; this can considerably degrade optical performance even near the sample surface. The device's performance was evaluated by observing fluorescence beads. The device was inserted between the objective lens and microscope revolver and succeeded in improving the spatial resolution and fluorescence signal of a bead image that was originally degraded by asymmetric aberration. Finally, we implemented the device for observing a fixed whole mouse brain with a sloping surface shape and complicated internal refractive-index distribution. The correction with the device improved the spatial resolution and increased the fluorescence signal by ˜2.4×. The device can provide a simple approach to acquiring higher-quality images of biospecimens.

  20. 3-Month experience in presbyopic correction with bi-aspheric multifocal central presbyLASIK treatments for hyperopia and myopia with or without astigmatism

    PubMed Central

    Luger, Michiel H.A.; Ewering, Tobias; Arba-Mosquera, Samuel

    2012-01-01

    Purpose To analyze simultaneous vision (distance and near) 3-month after bi-aspheric multifocal central presbyLASIK treatments for hyperopia and myopia with or without astigmatism. Methods Retrospective study analyzing patients that had been treated for correcting distance ametropiae and alleviating presbyopic symptoms simultaneously. All patients had been treated in Presby Aspheric mode using FemtoLASIK. No eye had previous corneal refractive surgery. Preoperative corneal curvature ranged between 40 D and 48 D, with pachymetry thicker than 500 μm. Preoperative best distance corrected visual acuity (CDVA) was 0.1 LogMAR or better, with best corrected near vision (CNVA) of 0.2 LogRAD or better. Results 66 patients treated using PresbyMAX software (SCHWIND eye-tech-solutions GmbH and Co. KG, Kleinostheim, Germany) were reviewed. For 24 patients, 3-month follow-up was completed. At 3 months, 71% of patients achieved UDVA 0.1 LogMAR or better, 79% patients obtained UNVA 0.1 LogRAD or better, and 83% of eyes were within 0.75 diopters (D) of defocus. Postoperative mean spherical equivalent refraction was −0.15 ± 0.50 D. Stability was achieved from the 6-week follow-up. 92% of patients achieved UDVA 0.2 LogMAR or better and UNVA 0.2 LogRAD or better. No statistical differences between myopes/hyperopes or between males/females were found. Conclusions Patient selection and expectation management are essential to achieve patient satisfaction. Even though optically the results are quite predictable, some patients find it difficult to adapt to the compromise between far and near vision, and others are dissatisfied by the minor loss of distance VA.

  1. Heritability of corneal refraction and corneal astigmatism: a population-based twin study among 66- to 79-year-old female twins.

    PubMed

    Pärssinen, Olavi; Kauppinen, Markku; Kaprio, Jaakko; Koskenvuo, Markku; Rantanen, Taina

    2013-03-01

    To examine the heritability of corneal refraction power (CR) and corneal astigmatism (AST) in older women. Corneal refraction and AST were measured by IOL master in 52 monozygotic (MZ) and 47 dizygotic (DZ) female twin pairs aged 66-79 years. The relative contribution of genetic and environmental factors to individual differences in CR was estimated by applying an independent pathway model to the twin data and AST by intraclass correlations (ICC). For the right eye, mean CR was 44.58 dioptres (D) (standard deviation (SD) ±1.28) When comparing CR of the right and left eye between MZ and DZ, no significant difference was found. Mean AST was 0.77 D (SD ±0.44) with no differences observed either between the MZ and the DZ individuals, or between the left and the right eyes. ICCs between the sisters for CR were, for the right eye, 0.882 and 0.378 for MZ and DZ, respectively, and for the left eye 0.855 and 0.358. For AST of the right eye, the ICCs were 0.533 and 0.096 for the MZ and DZ pairs, respectively, and for the left eye, the MZ and DZ correlations were 0.396 and 0.299. Quantitative genetic modelling showed that 81% of the variance in CR could be explained by genetic factors, additive genetic factors explaining 62% (95% confidence interval [CI] 44% -86%) and dominant genetic effect 19% (95% CI 7-49%) of the variance in CR. Different models were constructed to explain the heredity of AST. None of these models gave meaningful results, although the ICC values for MZ were higher than those for DZ. Most of the variance in CR among older Finnish women could be explained by genetic factors. © 2012 The Authors. Acta Ophthalmologica © 2012 Acta Ophthalmologica Scandinavica Foundation.

  2. Comparison of corneal power, astigmatism, and wavefront aberration measurements obtained by a point-source color light-emitting diode-based topographer, a Placido-disk topographer, and a combined Placido and dual Scheimpflug device.

    PubMed

    Ventura, Bruna V; Wang, Li; Ali, Shazia F; Koch, Douglas D; Weikert, Mitchell P

    2015-08-01

    To evaluate and compare the performance of a point-source color light-emitting diode (LED)-based topographer (color-LED) in measuring anterior corneal power and aberrations with that of a Placido-disk topographer and a combined Placido and dual Scheimpflug device. Cullen Eye Institute, Baylor College of Medicine, Houston, Texas USA. Retrospective observational case series. Normal eyes and post-refractive-surgery eyes were consecutively measured using color-LED, Placido, and dual-Scheimpflug devices. The main outcome measures were anterior corneal power, astigmatism, and higher-order aberrations (HOAs) (6.0 mm pupil), which were compared using the t test. There were no statistically significant differences in corneal power measurements in normal and post-refractive surgery eyes and in astigmatism magnitude in post-refractive surgery eyes between the color-LED device and Placido or dual Scheimpflug devices (all P > .05). In normal eyes, there were no statistically significant differences in 3rd-order coma and 4th-order spherical aberration between the color-LED and Placido devices and in HOA root mean square, 3rd-order coma, 3rd-order trefoil, 4th-order spherical aberration, and 4th-order secondary astigmatism between the color-LED and dual Scheimpflug devices (all P > .05). In post-refractive surgery eyes, the color-LED device agreed with the Placido and dual-Scheimpflug devices regarding 3rd-order coma and 4th-order spherical aberration (all P > .05). In normal and post-refractive surgery eyes, all 3 devices were comparable with respect to corneal power. The agreement in corneal aberrations varied. Drs. Wang, Koch, and Weikert are consultants to Ziemer Ophthalmic Systems AG. Dr. Koch is a consultant to Abbott Medical Optics, Inc., Alcon Surgical, Inc., and i-Optics Corp. Copyright © 2015 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  3. Corneal astigmatism measuring module for slit lamps

    NASA Astrophysics Data System (ADS)

    Ventura, L.; Riul, C.; Sousa, S. J. F.; DeGroote, J. G. S.; Rosa Filho, A. B.; Oliveira, G. C. D.

    2006-06-01

    We have developed an automatic keratometer module for slit lamps that provides automatic measurements of the radii of the corneal curvature. The system projects 72 light spots displayed in a precise circle at the examined cornea. The displacement and deformation of the reflected image of these light spots are analysed providing the keratometry. Measurements in the range of 26.8-75 D can be obtained and a self-calibration system has been specially designed in order to keep the system calibrated. Infrared LEDs indicate automatically which eye is being examined. Volunteer patients (492) have been submitted to the system and the results show that our system has a high correlation factor with the commercially available manual keratometers and the keratometry measurements from a topographer. Our developed system is 95% in agreement with the corneal topographer (Humphrey—Atlas 995 CZM) and the manual keratometer (Topcon OM-4). The system's nominal precision is 0.05 mm for the radii of curvature and 1° for the associated axis. This research has been supported by Fundação de Apoio à Pesquisa do Estado de São Paulo (FAPESP).

  4. Paraxial ocular rotation with astigmatic lenses.

    PubMed

    Flores, Jose Ramon

    2010-12-01

    To obtain analytical formulas for calculating the ocular rotation and the prismatic effect with a general lens, centered or decentered, with particular reference to thick spherotoric spectacle lenses. Linear theory is used, using the symplectic properties of optical matrices, to derive the desired formulas. By applying the general formulas to particular cases, the corresponding formulas are obtained, sometimes recovering formulas already known. Two examples serve to illustrate the use of the formulas obtained and to compare the results they provide with the ones obtained by exact ray tracing. The linear formulas derived allow to find, in a rather easy way, quite accurate values of the ocular rotation and the prismatic effect in the paraxial region.

  5. Cancellation of RF Coupler-Induced Emittance Due to Astigmatism

    SciTech Connect

    Dowell, David

    2016-12-11

    It is well-known that the electron beam quality required for applications such as FEL’s and ultra-fast electron diffraction can be degraded by the asymmetric fields introduced by the RF couplers of superconducting linacs. This effect is especially troublesome in the injector where the low energy beam from the gun is captured into the first high gradient accelerator section. Unfortunately modifying the established cavity design is expensive and time consuming, especially considering that only one or two sections are needed for an injector. Instead, it is important to analyze the coupler fields to understand their characteristics and help find less costly solutions for their cancellation and mitigation. This paper finds the RF coupler-induced emittance for short bunches is mostly due to the transverse spatial sloping or tilt of the field, rather than the field’s time-dependence. It is shown that the distorting effects of the coupler can be canceled with a static (DC) quadrupole lens rotated about the z-axis.

  6. Geometric phases in astigmatic optical modes of arbitrary order

    SciTech Connect

    Habraken, Steven J. M.; Nienhuis, Gerard

    2010-08-15

    The transverse spatial structure of a paraxial beam of light is fully characterized by a set of parameters that vary only slowly under free propagation. They specify bosonic ladder operators that connect modes of different orders, in analogy to the ladder operators connecting harmonic-oscillator wave functions. The parameter spaces underlying sets of higher-order modes are isomorphic to the parameter space of the ladder operators. We study the geometry of this space and the geometric phase that arises from it. This phase constitutes the ultimate generalization of the Gouy phase in paraxial wave optics. It reduces to the ordinary Gouy phase and the geometric phase of nonastigmatic optical modes with orbital angular momentum in limiting cases. We briefly discuss the well-known analogy between geometric phases and the Aharonov-Bohm effect, which provides some complementary insights into the geometric nature and origin of the generalized Gouy phase shift. Our method also applies to the quantum-mechanical description of wave packets. It allows for obtaining complete sets of normalized solutions of the Schroedinger equation. Cyclic transformations of such wave packets give rise to a phase shift, which has a geometric interpretation in terms of the other degrees of freedom involved.

  7. Increase in velocimeter depth of focus through astigmatism

    SciTech Connect

    Erskine, D.J.

    1996-05-01

    Frequently, velocimeter targets are illuminated by a laser beam passing through a hole in a mirror. This mirror is responsible for diverting returning light from a target lens to a velocity interferometer system for any reflector (VISAR). This mirror is often a significant distance from the target lens. Consequently, at certain target focus positions the returning light is strongly vignetted by the hole, causing a loss of signal. We find that we can prevent loss of signal and greatly increase the useful depth of focus by attaching a cylindrical lens to the target lens. {copyright} {ital 1996 American Institute of Physics.}

  8. Increase in velocimeter depth of focus through astigmatism

    SciTech Connect

    Erskine, D.J.

    1995-11-01

    Frequently, velocimeter targets are illuminated by a laser beam passing through a hole in a mirror. This mirror is responsible for diverting returning light from a target lens to a velocity interferometer system for any reflector. This mirror is often a significant distance from the target lens. Consequently, at certain target focus positions the returning light is strongly vignetted by the hole, causing a loss of signal. This note finds that the loss of signal can be prevented and that the useful depth can be greatly increased by attaching a cylindrical lens to the target lens. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  9. Mode locking with a compensated space--time astigmatism

    SciTech Connect

    Christov, I.P.; Stoev, V.D.; Murnane, M.M.; Kapteyn, H.C.

    1995-10-15

    We present what is to our knowledge the first full spatial plus temporal model of a self-mode-locked titanium-doped sapphire laser. The self-consistent evolution of the pulse toward steady state imposes strong space--time focusing in the crystal, where both the space and time foci are located. This combined focusing significantly improves the discrimination properties of the nonlinear resonator for shorter pulses and reduces the transient stage of pulse formation. Our theoretical results are in very good agreement with experiment. {copyright} {ital 1995} {ital Optical} {ital Society} {ital of} {ital America}.

  10. Controlling astigmatism and polarization in a stripe heterojunction laser

    SciTech Connect

    Boroshnev, A.V.; Gorshkova, O.A.; Kobyakova, M.S.; Okhotnikov, O.G.; Pak, G.T.; Shavvo, I.A.

    1985-02-01

    It is shown that it is possible to change the waveguide properties of a heterojunction laser and to control its optical characteristics in a single heterostructure fabricated on a substrate with a terraced profile. (AIP)

  11. Increase in velocimeter depth of focus through astigmatism. Revision 1

    SciTech Connect

    Erskine, D.J.

    1995-09-26

    Frequently, velocimeter targets are illuminated by a laser beam passing through a hole in a mirror. This mirror is responsible for diverting returning light from a target lens to a velocity interferometer system for any reflector (VISAR). This mirror is often a significant distance from the target lens. Consequently, at certain target focus positions the returning light is strongly vignetted by the hole, causing a loss of signal. The authors find that they can prevent loss of signal and greatly increase the useful depth of focus by attaching a cylindrical lens to the target lens.

  12. 3D holographic head mounted display using holographic optical elements with astigmatism aberration compensation.

    PubMed

    Yeom, Han-Ju; Kim, Hee-Jae; Kim, Seong-Bok; Zhang, HuiJun; Li, BoNi; Ji, Yeong-Min; Kim, Sang-Hoo; Park, Jae-Hyeung

    2015-12-14

    We propose a bar-type three-dimensional holographic head mounted display using two holographic optical elements. Conventional stereoscopic head mounted displays may suffer from eye fatigue because the images presented to each eye are two-dimensional ones, which causes mismatch between the accommodation and vergence responses of the eye. The proposed holographic head mounted display delivers three-dimensional holographic images to each eye, removing the eye fatigue problem. In this paper, we discuss the configuration of the bar-type waveguide head mounted displays and analyze the aberration caused by the non-symmetric diffraction angle of the holographic optical elements which are used as input and output couplers. Pre-distortion of the hologram is also proposed in the paper to compensate the aberration. The experimental results show that proposed head mounted display can present three-dimensional see-through holographic images to each eye with correct focus cues.

  13. High-speed atomic force microscope based on an astigmatic detection system

    SciTech Connect

    Liao, H.-S.; Chen, Y.-H.; Hwu, E.-T.; Chang, C.-S.; Hwang, I.-S.; Ding, R.-F.; Huang, H.-F.; Wang, W.-M.; Huang, K.-Y.

    2014-10-15

    High-speed atomic force microscopy (HS-AFM) enables visualizing dynamic behaviors of biological molecules under physiological conditions at a temporal resolution of 1s or shorter. A small cantilever with a high resonance frequency is crucial in increasing the scan speed. However, detecting mechanical resonances of small cantilevers is technically challenging. In this study, we constructed an atomic force microscope using a digital versatile disc (DVD) pickup head to detect cantilever deflections. In addition, a flexure-guided scanner and a sinusoidal scan method were implemented. In this work, we imaged a grating sample in air by using a regular cantilever and a small cantilever with a resonance frequency of 5.5 MHz. Poor tracking was seen at the scan rate of 50 line/s when a cantilever for regular AFM imaging was used. Using a small cantilever at the scan rate of 100 line/s revealed no significant degradation in the topographic images. The results indicate that a smaller cantilever can achieve a higher scan rate and superior force sensitivity. This work shows the potential for using a DVD pickup head in future HS-AFM technology.

  14. Epithelial Thickness Profile Changes Following Small Incision Refractive Lenticule Extraction (SMILE) for Myopia and Myopic Astigmatism.

    PubMed

    Ganesh, Sri; Brar, Sheetal; Relekar, Kirti J

    2016-07-01

    To evaluate the epithelial thickness profile changes following small incision refractive lenticule extraction (SMILE) and study their correlation with the amount of myopia corrected. Epithelial thickness was measured in nine zones with spectral-domain anterior segment optical coherence tomography (SD-OCT) across a 6-mm diameter preoperatively and at 1 day, 2 weeks, and 3 months postoperatively. The observed changes were correlated with the degree of myopia corrected. The study included 100 eyes from 50 eligible patients (32 females, 18 males) with a mean age of 24.4 ± 2.8 years. Thirty-eight eyes underwent SMILE for low (spherical equivalent [SE] < -4.00 diopters [D]), 44 eyes for moderate (SE -4.00 to -6.00 D), and 18 eyes for high (SE > -6.00 to -10.00 D) myopia with 6.71 ± 1.65, 6.82 ± 0.21, and 6.44 ± 0.2 mm optical zones, respectively. At 3 months, a statistically significant epithelial thickness increase was observed in the central zone (6.83% for low, 9.26% for moderate, and 12.7% for high myopia, P < .05 for all groups) and superior zone (3.98% for low, 7.82% for moderate, and 9.87% for high myopia) across all three groups, which correlated positively with the degree of myopia corrected (r(2) = 0.723 for central zone, r(2) = 0.585 for superior zone, P < .001 for both zones). None of the other zones showed any statistically significant changes at 3 months. Four eyes of two patients with high myopia (SE > -8.00 D) had regression due to significant epithelial thickening. Preliminary results suggest that epithelial thickness profile changes after SMILE may have an impact on the refractive outcome in the long-term postoperative period, especially in higher degrees of myopia. [J Refract Surg. 2016;32(7):473-478.]. Copyright 2016, SLACK Incorporated.

  15. High-speed atomic force microscope based on an astigmatic detection system

    NASA Astrophysics Data System (ADS)

    Liao, H.-S.; Chen, Y.-H.; Ding, R.-F.; Huang, H.-F.; Wang, W.-M.; Hwu, E.-T.; Huang, K.-Y.; Chang, C.-S.; Hwang, I.-S.

    2014-10-01

    High-speed atomic force microscopy (HS-AFM) enables visualizing dynamic behaviors of biological molecules under physiological conditions at a temporal resolution of 1s or shorter. A small cantilever with a high resonance frequency is crucial in increasing the scan speed. However, detecting mechanical resonances of small cantilevers is technically challenging. In this study, we constructed an atomic force microscope using a digital versatile disc (DVD) pickup head to detect cantilever deflections. In addition, a flexure-guided scanner and a sinusoidal scan method were implemented. In this work, we imaged a grating sample in air by using a regular cantilever and a small cantilever with a resonance frequency of 5.5 MHz. Poor tracking was seen at the scan rate of 50 line/s when a cantilever for regular AFM imaging was used. Using a small cantilever at the scan rate of 100 line/s revealed no significant degradation in the topographic images. The results indicate that a smaller cantilever can achieve a higher scan rate and superior force sensitivity. This work shows the potential for using a DVD pickup head in future HS-AFM technology.

  16. Electromagnetic Resonance of Astigmatic Gaussian Beam to the High Frequency Gravitational Waves

    NASA Astrophysics Data System (ADS)

    Zhong, Yuan-Hong; Li, Jin; Zhou, Yao; Lei, Qi-Lun

    2016-10-01

    Not Available Supported by the National Natural Science Foundation of China under Grant Nos 11205254 and 61501069, and the Fundamental Research Funds for the Central Universities under Grant No 106112016CDJXY300002.

  17. Quantifying Assessments of Vision Improvements for Myopes, Hypermetropes, Presbyopes, and Astigmats, in Brazil and Elsewhere.

    NASA Astrophysics Data System (ADS)

    Lopes, Demetriou; D. M., D.; Niemi, Paul N.; D., O.; Mc Leod, Roger D.

    2007-10-01

    Vision can safely, rapidly, and significantly be improved among nearsighted, far-sighted, presbyopic, and astigmatatic individuals, using methods developed for Mc Leod's patent-pending Naturoptics. We hope to calibrate and apply the method in South America, particularly Brazil, using metric standards accessible from ordinary vision assessment charts as used there. This precursor for extension into Hispanic-speaking areas, especially Chile, Guatemala, Honduras, Mexico, Paraguay, Peru, and Puerto Rico, is to establish property-rights protected licensed teaching agreements. Initially, visually impaired potential students of to-be-established not-for-profit Naturopathic medical, surgical, dental, law, science, and arts schools, perhaps named Metocantins or Metaquaratinga University, if in Brazil, will learn to correct their vision; training and licensing them can provide earnings for the self-funding of all associated activities and expenses. We will publish established results that refute claims relating to vision. Mc Leod's spatial Fourier transform model for retinal focal surface electric field amplitude vision explains all phenomena and Land's two-wavelength interval color vision results.

  18. Topography-guided photorefractive keratectomy for irregular astigmatism after small incision lenticule extraction.

    PubMed

    Ivarsen, Anders; Hjortdal, Jesper Ø

    2014-06-01

    To report the outcome of topography-guided photorefractive keratectomy (PRK) after complicated small incision lenticule extraction (SMILE). Retrospective case series of 5 eyes with irregular topography and ghost images after complicated SMILE. All eyes received transepithelial topography-guided PRK. Two eyes were treated with 0.02% mitomycin C. Patients were examined after a minimum of 3 months with evaluation of uncorrected (UDVA) and corrected (CDVA) distance visual acuity, Pentacam tomography (Oculus Optikgeräte, Wetzlar, Germany), and whole-eye aberrometry. In 3 eyes, subjective symptoms were diminished and UDVA, CDVA, topography, and corneal wavefront aberrations were improved. The remaining 2 eyes developed significant haze with worsened topography and wavefront aberrations. One eye experienced a two-line reduction in CDVA. Eyes with haze development had not been treated with mitomycin C. Transepithelial topography-guided PRK may reduce visual symptoms after complicated SMILE if postoperative haze can be controlled. To reduce the risk of haze development, application of mitomycin C may be considered. Copyright 2014, SLACK Incorporated.

  19. Mitochondria-rich cells in the astigmatic mites, Diplaegidia columbae (Buchholz) (Analgidae) and Falculifer rostratus (Buchholz) (Falculiferidae) (Acari: Astigmata).

    PubMed

    Witaliński, Wojciech; Liana, Marcin

    2010-09-01

    Mitochondria are well-characterized intracellular organelles usually concentrated in locations of high energy consumption. Light microscopic and transmission electron microscopic observations of the internal anatomy of the feather mites Diplaegidia columbae and Falculifer rostratus were conducted. In the anterior half of the bodies of the mites, we found several dozen of distinctive mitochondria-rich (MR) cells filled with abundant, large mitochondria. Mitochondria are placed individually or enclosed in small groups within an elaborated lamellar system forming a mitochondria-lamellae complex (MLC). The role of the MLC as well as the MR cells is not clear at present, but their involvement in heat generation is hypothesized and briefly discussed.

  20. Comparison of visual and refractive outcomes following femtosecond laser- assisted lasik with smile in patients with myopia or myopic astigmatism.

    PubMed

    Ganesh, Sri; Gupta, Rishika

    2014-09-01

    To compare the visual and refractive out-comes of femtosecond laser-assisted LASIK with small-incision lenticule extraction (SMILE) in terms of visual acuity, contrast sensitivity, aberrations, and dry eye. A single-center prospective randomized study in which patients diagnosed as having myopia presenting for refractive correction were allocated to either a LASIK or SMILE group. The primary outcome measures were refractive efficacy, predictability, and safety, postoperative contrast sensitivity, aberrations, and dry eye status. Patients were followed up at days 1 and 15 and 3 months; postoperative uncorrected visual acuity (UCVA), aberrations, dry eye, and contrast sensitivity were recorded and compared to preoperative data. Two postoperative subjective questionnaires were used to assess pain, pricking sensation, redness, glare, and overall patient satisfaction. At day 1 postoperatively, 48 (96%) of 50 eyes in the SMILE group achieved a UCVA of 20/20 compared with 46 (92%) of 50 eyes in the LASIK group. At day 15 postoperatively, contrast sensitivity was similar in the two groups (P = .15), but by 3 months, it was better in the SMILE group than the LASIK group at all spatial frequencies (P < .0001). At 3 months postoperatively, 42 (84%) eyes in each group achieved a UCVA of 20/20, with 6 (12%) eyes in the SMILE group and 2 (4%) eyes in the LASIK group achieving 20/15. Higher-order aberrations at 3 months postoperatively were significantly higher in the LASIK group (0.437 + 0.103 pm) than in the SMILE group (0.267 + 0.07 pm; P < .001). Postoperative dry eye and glare were significantly more common following LASIK (P < .001). Three-month results demonstrate that refractive accuracy, dry eye, contrast, and induced aberrations are better following SMILE rather than LASIK.

  1. Management of Extreme Ametropia after Penetrating Keratoplasty: A Series of Surgical Procedures for High Myopia and Astigmatism

    PubMed Central

    Valdez-Garcia, Jorge E.; Cueto-Gómez, Juan J.; Lozano-Ramírez, Juan F.; Tamez-Peña, Alejandro E.

    2014-01-01

    A series of surgical interventions – relaxing corneal incisions, intraocular lens, and intrastromal rings – were used to correct a case of extreme ametropia in a thin cornea after a penetrating keratoplasty in an 18-year-old patient who presented with a −10.25 −8.50 × 120 preoperative refraction and 20/200 best-corrected visual acuity (BCVA). After a series of surgical procedures, the patient's BCVA in his left eye improved to 20/30 with +0.50 −1.00 × 170, the slit lamp examination showed no significant findings, and the patient's visual complaints disappeared. At the 1-year follow-up, the BCVA was 20/25, without visual complaints. The process of individualizing the surgical procedure in the present case was employed in an outcome-based approach, that is, the next surgical procedure was defined after the surgery and postoperative evaluation. The patient did not present complications during the follow-up period of 2.5 years. PMID:25232339

  2. Long-term Visual and Refractive Outcomes After LASIK for High Myopia and Astigmatism From -8.00 to -14.25 D.

    PubMed

    Reinstein, Dan Z; Carp, Glenn I; Archer, Timothy J; Lewis, Tariq A; Gobbe, Marine; Moore, Johnny; Moore, Tara

    2016-05-01

    To evaluate outcomes of high myopic LASIK using the MEL 80 excimer laser (Carl Zeiss Meditec, Jena, Germany). Retrospective analysis of 479 consecutive high myopic LASIK procedures (318 patients) using the MEL 80 excimer laser and VisuMax femtosecond laser (Carl Zeiss Meditec) in 77% of cases or zero compression Hansatome microkeratome (Bausch & Lomb, Rochester, NY) in 23% of cases. Inclusion criteria were preoperative spherical equivalent refraction (SEQ) of between -8.00 and -14.25 diopters (D) and corrected distance visual acuity (CDVA) of 20/20 or better. Patients were observed for a minimum of 1 year. Flap thickness was between 80 and 160 µm and optical zone was between 5.75 and 6.50 mm. Standard outcomes analysis was performed. Mean attempted SEQ was -9.39 ± 1.22 D (range: -8.00 to -14.18 D) and mean cylinder was -1.03 ± 0.84 D (range: 0.00 to -4.50 D). Mean age was 37 ± 9 years (range: 21 to 60 years) with 54% female patients. Postoperative SEQ was ±0.50 D in 55% and ±1.00 D in 83% of eyes after primary treatment. After re-treatment, 69% of eyes were within ±0.50 D and 95% were within ±1.00 D. UDVA was 20/20 or better in 89% of eyes after final treatment. One line of CDVA was lost in 3% of eyes and no eyes lost two or more lines. Statistically significant increases (P < .001) were measured in contrast sensitivity (CSV-1000) at 12 and 18 cycles per degree. The MEL 80 excimer laser was found to achieve high efficacy and safety for treatment of high myopia between -8.00 and -14.25 D and up to -4.50 D of cylinder. [J Refract Surg. 2016;32(5):290-297.]. Copyright 2016, SLACK Incorporated.

  3. Posterior Corneal Characteristics of Cataract Patients with High Myopia

    PubMed Central

    Jing, Qinghe; Tang, Yating; Qian, Dongjin; Lu, Yi; Jiang, Yongxiang

    2016-01-01

    Purpose To evaluate the characteristics of the posterior corneal surface in patients with high myopia before cataract surgery. Methods We performed a cross-sectional study at the Eye and ENT Hospital of Fudan University, Shanghai, China. Corneal astigmatism and axial length were measured with a rotating Scheimpflug camera (Pentacam) and partial coherence interferometry (IOLMaster) in a high-myopia study group of 167 eyes (axial length ≥ 26 mm) and a control group of 150 eyes (axial length > 20 mm and < 25 mm). Results Total corneal astigmatism and anterior corneal astigmatism values were higher in the high-myopia group than in the control group. There was no significant difference in posterior corneal astigmatism between the high-myopia study group and the control group. In the study group, the mean posterior corneal astigmatism (range 0 – −0.9 diopters) was –0.29 diopters (D) ± 0.17 standard deviations (SD). The steep corneal meridian was aligned vertically (60°–120°) in 87.43% of eyes for the posterior corneal surface, and did not change with increasing age. There was a significant correlation (r = 0.235, p = 0.002) between posterior corneal astigmatism and anterior corneal astigmatism, especially when the anterior corneal surface showed with-the-rule (WTR) astigmatism (r = 0.452, p = 0.000). There was a weak negative correlation between posterior corneal astigmatism and age (r = –0.15, p = 0.053) in the high-myopia group. Compared with total corneal astigmatism values, the anterior corneal measurements alone overestimated WTR astigmatism by a mean of 0.27 ± 0.18 D in 68.75% of eyes, underestimated against-the-rule (ATR) astigmatism by a mean of 0.41 ± 0.28 D in 88.89% of eyes, and underestimated oblique astigmatism by a mean of 0.24 ± 0.13 D in 63.64% of eyes. Conclusions Posterior corneal astigmatism decreased with age and remained as ATR astigmatism in most cases of high myopia. There was a significant correlation between posterior corneal

  4. Posterior Corneal Characteristics of Cataract Patients with High Myopia.

    PubMed

    Jing, Qinghe; Tang, Yating; Qian, Dongjin; Lu, Yi; Jiang, Yongxiang

    2016-01-01

    To evaluate the characteristics of the posterior corneal surface in patients with high myopia before cataract surgery. We performed a cross-sectional study at the Eye and ENT Hospital of Fudan University, Shanghai, China. Corneal astigmatism and axial length were measured with a rotating Scheimpflug camera (Pentacam) and partial coherence interferometry (IOLMaster) in a high-myopia study group of 167 eyes (axial length ≥ 26 mm) and a control group of 150 eyes (axial length > 20 mm and < 25 mm). Total corneal astigmatism and anterior corneal astigmatism values were higher in the high-myopia group than in the control group. There was no significant difference in posterior corneal astigmatism between the high-myopia study group and the control group. In the study group, the mean posterior corneal astigmatism (range 0 - -0.9 diopters) was -0.29 diopters (D) ± 0.17 standard deviations (SD). The steep corneal meridian was aligned vertically (60°-120°) in 87.43% of eyes for the posterior corneal surface, and did not change with increasing age. There was a significant correlation (r = 0.235, p = 0.002) between posterior corneal astigmatism and anterior corneal astigmatism, especially when the anterior corneal surface showed with-the-rule (WTR) astigmatism (r = 0.452, p = 0.000). There was a weak negative correlation between posterior corneal astigmatism and age (r = -0.15, p = 0.053) in the high-myopia group. Compared with total corneal astigmatism values, the anterior corneal measurements alone overestimated WTR astigmatism by a mean of 0.27 ± 0.18 D in 68.75% of eyes, underestimated against-the-rule (ATR) astigmatism by a mean of 0.41 ± 0.28 D in 88.89% of eyes, and underestimated oblique astigmatism by a mean of 0.24 ± 0.13 D in 63.64% of eyes. Posterior corneal astigmatism decreased with age and remained as ATR astigmatism in most cases of high myopia. There was a significant correlation between posterior corneal astigmatism and anterior corneal astigmatism

  5. Proposed classification for topographic patterns seen after penetrating keratoplasty

    PubMed Central

    Karabatsas, C.; Cook, S.; Sparrow, J.

    1999-01-01

    AIMS—To create a clinically useful classification for post-keratoplasty corneas based on corneal topography.
METHODS—A total of 360 topographic maps obtained with the TMS-1, from 95 eyes that had undergone penetrating keratoplasty (PKP), were reviewed independently by two examiners in a masked fashion, and were categorised according to a proposed classification scheme.
RESULTS—A high interobserver agreement (88% in the first categorisation) was achieved. At 12 months post-PKP, a regular astigmatic pattern was observed in 20/85 cases (24%). This was subclassified as oval in three cases (4%), oblate symmetric bow tie in six cases (7%), prolate asymmetric bow tie in six cases (7%), and oblate asymmetric bow tie in five cases (6%). An irregular astigmatic pattern was observed in 61/85 cases (72%), subclassified as prolate irregular in five cases (6%), oblate irregular in four cases (5%), mixed in seven cases (8%), steep/flat in 11 cases (13%), localised steepness in 16 cases (19%), and triple pattern in three cases (4%). Regular astigmatic patterns were associated with significantly higher astigmatism measurements. The surface asymmetry index was significantly lower in the regular astigmatic patterns.
CONCLUSIONS—In post-PKP corneas, the prevalence of irregular astigmatism is about double that of regular astigmatism, with a trend for increase of the irregular patterns over time.

 Keywords: keratoplasty; corneal topography; astigmatism PMID:10434860

  6. Which image parameter(s) for the automation of the electron microscope?

    PubMed

    Bonnet, N; Zinzindohoue, P

    1989-03-01

    Experiments on automating the transmission electron microscope rely on the search for minimum variance. This image parameter gives satisfactory results for automatic focusing, astigmatism correction, and beam alignment. We investigate here the different image descriptors that might also be used; we conclude that texture parameters, which are directional, would be better candidates correcting astigmatism and beam tilt.

  7. Beam Characteristics of Mid-IR Quantum Cascade Lasers

    SciTech Connect

    Krishnaswami, Kannan; Bernacki, Bruce E.; Cannon, Bret D.; Phillips, Mark C.; Ho, Nicolas; Allen, Paul J.; Anheier, Norman C.

    2007-12-31

    We report divergence, astigmatism and M2 measurements for 8.77gm quantum cascade lasers. Measurements showed divergence of 62° by 32A° FWHM ± 2A° and M2 values of 1.81 and 1.22 for the fast and slow axes respectively. Astigmatism at source was ~4gm, less than half a wave.

  8. Surgical Treatment of Corneal Ectasia with Motowa's Trephine and Selective Suturing Technique

    PubMed Central

    Al-Motowa, Saeed; Al-Harby, Mosa

    2016-01-01

    A 40-year-old male presented with bilateral ectasia, contact lens intolerance, and astigmatism >10 D in both eyes. The patient had end-stage pellucid marginal degeneration that warranted surgical treatment. We present a unique surgical technique to stabilize the cornea, minimize astigmatism, improve vision and corneal status, and avoid penetrating keratoplasty. PMID:27994396

  9. Investigation of the 2-m telescope optics and seeing at the Terskol Peak Observatory

    NASA Astrophysics Data System (ADS)

    Butenko, G. Z.; Kuznetsov, V. I.; Snezhko, L. I.; Andruk, V. M.; Parusimov, V. G.; Sergeev, A. V.; Ivanov, Yu. S.

    2000-09-01

    We present the Hartmann images to attestate the Cassegrain focus optics of the 2-m telescope of the Peak Terskol Observatory of the International Center for Astronomical and Medico-Ecological Research of the NASU/RAS. The Cassegrain focus optics is a classical Ritchey-Chretien system with compensated coma and spherical aberration. The astigmatism corrector compensates for the system field astigmatism. Star images formed by the system with the astigmatism corrector are characterized by d0.8=1.''3, which does not meet the present-day requirements. The constant coma followed by the spherical aberration are dominating. The astigmatism is the least distortion of the image. Eliminating the Zeidel aberrations gives d0.8=0.''7, which coincides with manufacturer attestation. An additional adjustment should be made to achieve this image quality. Local wavefront errors including triangular astigmatism are small, which testifies that the unloading and fastening of the mirrors are of a high quality.

  10. Fourier analysis of videokeratography data: Clinical usefulness in grade I and subclinical keratoconus.

    PubMed

    Sideroudi, Haris; Labiris, Georgios; Georgatzoglou, Kimon; Ditzel, Fienke; Siganos, Charalambos; Kozobolis, Vassilios

    2016-05-01

    To evaluate the contribution of Fourier analysis of videokeratographic data in the diagnosis of subclinical keratoconus and keratoconus. Eye Institute of Thrace, Democritus University, Alexandroupolis, Greece. Observational case series. The following Pentacam-derived parameters, resulting from Fourier decomposition of keratometric data, were evaluated for their diagnostic capacity using receiver operating curves: spherical component and eccentricity, maximum decentration, regular astigmatism in the center and in the periphery, mean astigmatism, irregularities, regular astigmatism in the center plus the irregularities, and total astigmatism. Logistic regression was performed to identify a combined diagnostic model. The study comprised 80 keratoconus eyes, 55 eyes diagnosed with subclinical keratoconus, and 50 normal eyes. Significant differences were detected in spherical eccentricity, maximum decentration, irregularities, regular astigmatism in the center and in the periphery, regular astigmatism in the center plus the irregularities, mean astigmatism, and total astigmatism parameters between the groups. Almost all parameters had high diagnostic ability in both study groups (area under the curve >90%). Among individual parameters, those with the highest predictive accuracy were the regular astigmatism in the center plus the irregularities (subclinical keratoconus 97.6%, keratoconus 98.8%) and the maximum decentration (subclinical keratoconus 91.4%, keratoconus 98.5%). Sufficient predictive accuracy (subclinical keratoconus 99.4, keratoconus 100%) was identified in a diagnostic model that combined the regular astigmatism in the center plus the irregularities and the maximum decentration. Fourier decomposition of keratometric data provided parameters with high accuracy in differentiating corneas with subclinical keratoconus from normal corneas and should be included to allow prompt diagnosis of keratoconus. None of the authors has a financial or proprietary interest

  11. [3 1/2 years experiences with ECCE with tunnel incision].

    PubMed

    Häberle, H; Anders, N; Antoni, H J; Pham, D T; Wollensak, J

    1997-01-01

    Since January 1992 planned extracapsular cataract extraction (ECCE) is performed routinely with the no-stitch technique at our clinic. To minimize surgically induced astigmatism further, modified wound constructions for planned ECCE with on 1.1-mm tunnel width were evaluated. The follow-up time was up to 3 years postoperatively. For 250 eyes wound closure was performed prospectively either sutureless (n = 70), with a single perpendicular suture (n = 100) or cross sutures (n = 40) at the 12 o'clock position or sutureless in the temporal position (n = 40). The complication rate was 4% (filtering bleb, iris prolapse or transient hypotonia). There were no wound ruptures, but once endophthalmitis was observed. Late mean astigmatism after up to 3 years follow-up for vertical incision was 2.05 +/- 1.16 D (1.01 +/- 0.96 D preoperatively) for sutureless wound closure, 1.63 +/- 1.08 D (0.86 +/- 0.95 D) for perpendicular and 1.76 +/- 0.88 D (0.73 +/- 0.55 D) for cross-sutures. A temporal incision resulted in 0.78 +/- 0.52 D (1.0 +/- 0.69 D) of astigmatism and was only performed on eyes with against the rule astigmatism preoperatively. Surgically induced astigmatism was stabilized early. For with the rule astigmatism preoperatively, a 12 o'clock incision with a perpendicular single suture is recommended and for against the rule astigmatism, a temporal incision.

  12. Causes of subnormal vision in patients following cataract surgery at a tertiary hospital in Kashmir.

    PubMed

    Ahangar, Andleeb; Sufi, Aalia Rasool; Nabi, Mushood; Rather, Muddasar Hassan

    2014-10-01

    Cataract surgery is aimed at restoring sight to near normal vision. This study, conducted at the Department of Ophthalmology, Government Medical College, Srinagar, is an attempt to determine the causes of subnormal vision in patients following cataract surgery at a tertiary hospital in Kashmir. One hundred patients who underwent cataract surgery with an unaided visual acuity of <6/9 at 16 weeks postoperatively were included in the study. Postoperative follow-up examinations were conducted until the 16th week. Intraoperative and postoperative complications were recorded to determine the cause of subnormal vision. Of 100 patients, 40 underwent extracapsular cataract extraction (ECCE), 30 underwent small incision cataract surgery (SICS) and 30 underwent phacoemulsification. Seventy-five percent of the patients who underwent ECCE had postoperative astigmatism with a mean astigmatism of 2.2 ± 0.81 diopters at 16 weeks, with the majority having with-the-rule astigmatism. In the SICS group, 17 (56.6 %) patients had a mean postoperative astigmatism of 0.75 ± 0.40 diopters, with the majority (82.3 %) having against-the-rule (ATR) astigmatism. In the phacoemulsification group, 13 (43.3 %) of the patients had a mean postoperative astigmatism of 0.48 ± 0.23 diopters with the majority having ATR astigmatism. Other causes of subnormal vision were pseudophakic ametropia, posterior capsular opacity and intraoperative complications like posterior capsular rent and vitreous loss. Postoperative astigmatism was the major cause of subnormal vision with greater astigmatism seen in the ECCE group. Therefore, procedures like smaller incision sutureless surgery and careful biometry are advocated to improve visual outcome and patient satisfaction.

  13. Accuracy and validity of IK4 handheld video keratometer measurements in children

    PubMed Central

    Harvey, Erin M.; Miller, Joseph M.; Schwiegerling, Jim; Clifford-Donaldson, Candice E.; Green, Tina K.; Messer, Dawn H.; Dobson, Velma

    2011-01-01

    The Infant Keratometer (IK4) is a custom handheld instrument that was designed specifically to allow measurement of corneal astigmatism in infants as young as 6 months of age. In this study, accuracy of IK4 measurements using standard toric surfaces was within 0.25 D. Validity measurements obtained in 860 children aged 3–7 years demonstrated slightly higher astigmatism measurements in the IK4 than in the Retinomax K+. Measurement success was 98% using the IK4. The IK4 may prove to be clinically useful for screening children as young as 3 years of age at high risk for corneal astigmatism. PMID:21907130

  14. Cyanoacrylate glue treatment for persistent aqueous leak following postkeratoplasty relaxing incisions with compression sutures.

    PubMed

    Karabatsas, C H; Easty, D L

    In spite of improvements in surgical techniques, donor materials and postoperative care, high astigmatism remains a quite common problem following penetrating keratoplasty [1]. Whenever the residual astigmatism cannot be corrected with spectacles or contact lenses, surgical treatment is required. Relaxing incisions combined with compression sutures is one of the most common methods used for this purpose [2, 3]. We report herein a case of persistent aqueous leak following relaxing incisions for the correction of postkeratoplasty astigmatism. The leak failed to respond to a bandage contact lens and resuturing and was eventually successfully treated with the use of cyanoacrylate glue. A marked regression of the surgical effect was observed in this case.

  15. Ring lens focusing and push-pull tracking scheme for optical disk systems

    NASA Technical Reports Server (NTRS)

    Gerber, R.; Zambuto, J.; Erwin, J. K.; Mansuripur, M.

    1993-01-01

    An experimental comparison of the ring lens and the astigmatic techniques of generating focus-error-signal (FES) in optical disk systems reveals that the ring lens generates a FES over two times steeper than that produced by the astigmat. Partly due to this large slope and, in part, because of its diffraction-limited behavior, the ring lens scheme exhibits superior performance characteristics. In particular the undesirable signal known as 'feedthrough' (induced on the FES by track-crossings during the seek operation) is lower by a factor of six compared to that observed with the astigmatic method. The ring lens is easy to align and has reasonable tolerance for positioning errors.

  16. Comparison of designs of off-axis Gregorian telescopes for millimeter-wave large focal-plane arrays.

    PubMed

    Hanany, Shaul; Marrone, Daniel P

    2002-08-01

    We compare the diffraction-limited field of view (FOV) provided by four types of off-axis Gregorian telescopes: the classical Gregorian, the aplanatic Gregorian, and the designs that cancel astigmatism and both astigmatism and coma. The analysis is carried out with telescope parameters that are appropriate for satellite and balloonborne millimeter- and submillimeter-wave astrophysics. We find that the design that cancels both coma and astigmatism provides the largest flat FOV, approximately 21 square deg. We also find that the FOV can be increased by approximately 15% by means of optimizing the shape and location of the focal surface.

  17. Take Steps to Keep Your Sight | NIH MedlinePlus the Magazine

    MedlinePlus

    ... any warning signs. Fast Facts Many causes of blindness are preventable through timely treatment. Protect your eyesight ... far-sightedness, and astigmatism. The leading causes of blindness are cataracts, glaucoma, macular degeneration, and diabetic retinopathy. ...

  18. How to Keep Your Sight for Life

    MedlinePlus

    ... page please turn Javascript on. Fast Facts Most blindness is preventable through timely treatment. Protect your eyesight ... related blurriness, and astigmatism. The leading causes of blindness are cataracts, glaucoma, macular degeneration, and diabetic retinopathy. ...

  19. Contact Lens Visual Rehabilitation in Keratoconus and Corneal Keratoplasty

    PubMed Central

    Ozkurt, Yelda; Atakan, Mehmet; Gencaga, Tugba; Akkaya, Sezen

    2012-01-01

    Keratoconus is the most common corneal distrophy. It's a noninflammatory progressive thinning process that leads to conical ectasia of the cornea, causing high myopia and astigmatism. Many treatment choices include spectacle correction and contact lens wear, collagen cross linking, intracorneal ring segments implantation and finally keratoplasty. Contact lenses are commonly used to reduce astigmatism and increase vision. There are various types of lenses are available. We reviewed soft contact lenses, rigid gas permeable contact lenses, piggyback contact lenses, hybrid contact lenses and scleral-semiscleral contact lenses in keratoconus management. The surgical option is keratoplasty, but even after sutur removal, high astigmatism may stil exists. Therefore, contact lens is an adequate treatment option to correct astigmatism after keratoplasty. PMID:22292112

  20. Multifocal Toric Intraocular Lens for Traumatic Cataract in a Child

    PubMed Central

    Zeng, Yanfeng; Fan, Licheng; Lu, Peirong

    2016-01-01

    A child suffering from traumatic cataract and corneal astigmatism of 2.14 D had a phacoemulsification operation and implantation of a ReSTOR Toric intraocular lens (IOL) to correct the astigmatism. The primary outcome measurements were the uncorrected distance visual acuity (UDVA), uncorrected near vision at 40 cm, intraocular pressure, spherical equivalent refraction, residual astigmatism, corneal astigmatism, presence of unusual optical phenomena, and use of spectacles. At 7 months postoperatively, UDVA was maintained between 16/20 and 24/20, near vision was between J1 and J3, residual spherical refraction was 0–0.37 D, and residual refractive cylinder was between 0 and 0.67 D. A multifocal toric IOL can provide the possibility of satisfactory vision for both distant and near conditions without the use of spectacles to meet children's needs when studying and doing sports. Additionally, binocular vision can be reconstructed. This intervention, therefore, seems to be a satisfactory alternative. PMID:28101039

  1. NEW APPROACHES: Capriole (somersaults)

    NASA Astrophysics Data System (ADS)

    Ferraro, Pietro

    1998-11-01

    The optics of astigmatism can be explained by using a cylindrical lens and a coarse grating to demonstrate capriole, an apparent rotation caused by the magnification along orthogonal axes being different.

  2. Ptosis - infants and children

    MedlinePlus

    ... children; Congenital ptosis; Eyelid drooping - children; Eyelid drooping - amblyopia; Eyelid drooping - astigmatism ... is needed right away to prevent "lazy eye" (amblyopia) . The provider will also treat any eye problems ...

  3. Effects of an asymmetrically molded plastic objective lens on the push-pull tracking-error signal in an optical disk drive.

    PubMed

    Hung, K M

    2000-03-10

    The effects of a plastic objective lens's astigmatism on the push-pull tracking-error signal (TES) of an optical disk data storage system were investigated theoretically and experimentally. Astigmatism of plastic objective lenses arises commonly from the asymmetric deviation from their designed shape during the molding process. By carefully studying the aberration characteristics of the objective lens and including the astigmatism of the laser diode in the analysis, we can calculate the combined effects of astigmatism of these two components on the push-pull TES. It is found, from both the simulations and the experiments, that, by rotation of the objective lens about the optical axis, the peak-to-peak value of the push-pull TES varies with the lens's rotation angle, and a change as great as 340% in its value was observed in a given optical pickup.

  4. National Ignition Facility Beamline Pupil Relay Plane Location and Imaging

    SciTech Connect

    Korniski, R J; Lawson, J K

    2002-01-29

    Axial astigmatism can be introduced into the nominal design of an optical system by tilted and tilted-wedged plates. The pupil images in the National Ignition Facility experience many such components. Some ramifications will be explored.

  5. Measurement of the M² beam propagation factor using a focus-tunable liquid lens.

    PubMed

    Niederriter, Robert D; Gopinath, Juliet T; Siemens, Mark E

    2013-03-10

    We demonstrate motion-free beam quality M² measurements of stigmatic, simple astigmatic, and general astigmatic (twisted) beams using only a focus-tunable liquid lens and a CCD camera. We extend the variable-focus technique to the characterization of general astigmatic beams by measuring the 10 second-order moments of the power density distribution for the twisted beam produced by passage through multimode optical fiber. Our method measures the same M² values as the traditional variable-distance method for a wide range of laser beam sources, including nearly TEM(00) (M²≈1) and general astigmatic multimode beams (M²≈8). The method is simple and compact, with no moving parts or complex apparatus and measurement precision comparable to the standard variable-distance method.

  6. A method for the prescription of inexpensive spectacles by non-specialist healthcare workers: S-Glasses.

    PubMed

    Treacy, M P; Treacy, M G; Dimitrov, B D; Seager, F E; Stamp, M A; Murphy, C C

    2013-04-01

    Globally, 153 million people are visually impaired from uncorrected refractive error. The aim of this research was to verify a method whereby autorefractors could be used by non-specialist health-workers to prescribe spectacles, which used a small stock of preformed lenses that fit frames with standardised apertures. These spectacles were named S-Glasses (Smart Glasses). This prospective, single-cohort exploratory study enrolled 53 patients with 94 eligible eyes having uncorrected vision of 6/18 or worse. Eyes with best-corrected vision worse than 6/12 were excluded. An autorefractor was used to obtain refractions, which were adjusted so that eyes with astigmatism less than 2.00 dioptres (D) received spherical equivalent lenses, and eyes with more astigmatism received toric lenses with a 2.50 D cylindrical element set at one of four meridians. The primary outcome was to compare S-Glasses vision with the WHO definition of visual impairment (6/18). Where astigmatism was 2.00 D or greater, comparison with spherical equivalent was made. Mixed-model analysis with repeated effect was used to account for possible correlation between the vision of fellow eyes of the same individual. S-Glasses corrected 100% of eyes with astigmatism less than 3.00 D and 69% of eyes with astigmatism of 3.00 D or greater. Spherical equivalent lenses corrected 25% of eyes with astigmatism of 2.00-2.99 D and 11% with astigmatism of at least 3.00 D. S-Glasses could be beneficial to resource-poor populations without trained refractionists. This novel approach, using approximate toric lenses, results in superior vision for astigmatic patients compared with the practice of providing spherical equivalent alone.

  7. [Pitfalls in the determination of distance glasses].

    PubMed

    Lachenmayr, B

    2011-04-01

    The correct determination of distance glasses depends on a correct objective refraction and a subject determination of power and axis of a possible astigmatism in both a coarse and fine manner. In suitable cases a binocular fine refraction under polarized conditions with a red-green test should be performed. Special considerations have to be taken into account in cases of high unilateral congenital or acquired astigmatism as well as in case of congenital or acquired anisometropia or aniseiconia.

  8. Optical Design of Adaptive Optics Confocal Scanning Laser Ophthalmoscope with Two Deformable Mirrors.

    PubMed

    Yang, Jinsheng; Wang, Yuanyuan; Rao, Xuejun; Wei, Ling; Li, Xiqi; He, Yi

    2017-01-01

    We describe the optical design of a confocal scanning laser ophthalmoscope with two deformable mirrors. Spherical mirrors are used for pupil relay. Defocus aberration of the human eye is corrected by a Badal focusing structure and astigmatism aberration is corrected by a deformable mirror. The main optical system achieves a diffraction-limited performance through the entire scanning field (6 mm pupil, 3 degrees on pupil plane). The performance of the optical system, with correction of defocus and astigmatism, is also evaluated.

  9. AFOSR Technical Report Summaries, April-June 1986,

    DTIC Science & Technology

    1986-06-01

    One example which reveals this energy levels property is meridional amblyopia , an abnormal dependence of visual contrast sensitivity on orientation; it...Contrary to the generalization that meridional amblyopia is only founld in continuing astigmats. this cFe sugCests the potency of transient infant...astigmatism to include permianent neural anisotropy reywnrds: Visual anisotropy Matusrational plasticity, Meridional amblyopia , 20 modulatioi transfer AD AIG

  10. LASER BEAMS: Use of the fractional Fourier transform in π/2 converters of laser modes

    NASA Astrophysics Data System (ADS)

    Malyutin, A. A.

    2004-02-01

    The possibility of using the fractional Fourier transform (FrFT) in optical schemes for astigmatic π/2 converters of Hermite—Gaussian modes to donut Laguerre—Gaussian modes is considered. Several schemes of converters based on the FrFT of the half-integer and irrational orders are presented. The lowest FrFT order than can be used in astigmatic mode converters is found. The properties of converters based on the fractional and ordinary Fourier transforms are compared.

  11. Introduction of a Toric Intraocular Lens to a Non-Refractive Cataract Practice: Challenges and Outcomes

    PubMed Central

    Kirwan, Clare; Nolan, John M; Stack, Jim; Dooley, Ian; Moore, Johnny; Moore, Tara CB; Beatty, Stephen

    2016-01-01

    Aim To identify challenges inherent in introducing a toric intraocular lens (IOL) to a non-refractive cataract practice, and evaluate residual astigmatism achieved and its impact on patient satisfaction. Methods Following introduction of a toric IOL to a cataract practice with all procedures undertaken by a single, non-refractive, surgeon (SB), pre-operative, intra-operative and post-operative data was analysed. Attenuation of anticipated post-operative astigmatism was examined, and subjectively perceived visual functioning was assessed using validated questionnaires. Results Median difference vector (DV, the induced astigmatic change [by magnitude and axis] that would enable the initial surgery to achieve intended target) was 0.93D; median anticipated DV with a non-toric IOL was 2.38D. One eye exhibited 0.75D residual astigmatism, compared to 3.8D anticipated residual astigmatism with a non-toric IOL. 100% of respondents reported satisfaction of ≥ 6/10, with 37.84% of respondents entirely satisfied (10/10). 17 patients (38.63%) reported no symptoms of dysphotopsia (dysphoptosia score 0/10), only 3 respondents (6.8%) reported a clinically meaningful level of dysphotopsia (≥ 4/10). Mean post-operative NEI VF-11 score was 0.54 (+/-0.83; scale 0 – 4). Conclusion Use of a toric IOL to manage astigmatism during cataract surgery results in less post-operative astigmatism than a non-toric IOL, resulting in avoidance of unacceptable post-operative astigmatism. PMID:27830188

  12. Aberrations of sphero-cylindrical ophthalmic lenses.

    PubMed

    Malacara, Z; Malacara, D

    1990-04-01

    The authors have presented in two previous articles the graphic solutions resembling Tscherning ellipses, for spherical as well as for aspherical ophthalmic lenses free of astigmatism or power error. These solutions were exact, inasmuch as they were based on exact ray tracing, and not third-order theory as frequently done. In this paper sphero-cylindrical lenses are now analyzed, also using exact ray tracing. The functional dependence of the astigmatism and the power error for these lenses is described extensively.

  13. Cost analysis of a mini-facet heliostat

    NASA Astrophysics Data System (ADS)

    Hall, Colin; Pratt, Rodney; Farrant, David; Corsi, Clotilde; Pye, John; Coventry, Joe

    2017-06-01

    A significant problem with conventional heliostats is off-axis astigmatism, which increases the spot size at the central receiver, limiting the temperature and efficiency of solar thermal systems. Inspired by low-cost mini-actuators used for car wing mirrors, we examine the economic feasibility of a heliostat with individually adjustable mini-facets to correct astigmatic effects, and we compare three alternative tracking configurations.

  14. Collimation of Fast Wide-Field Telescopes

    NASA Astrophysics Data System (ADS)

    McLeod, Brian A.

    1996-02-01

    In this paper, I present a simple technique for collimating the secondary mirror of fast focal ratio wide-field Cassegrain telescopes. This technique minimizes both coma and astigmatism across the field. Because astigmatism is nearly zero on-axis even in a misaligned system, it is necessary to make measurements off-axis. This technique is useful on telescopes corrected for off-axis coma such as Ritchey-Cretien designs and classical Cassegrains with refractive correctors. Proper alignment for astigmatism is especially important in the latter type of telescope where there is no astigmatism across the field in a properly aligned system. The tools required for collimation are a camera that can examine images at several locations at the edge of the field and a secondary mirror that can be controlled in five axes. Also presented are analytic expressions for the amount of field-dependent astigmatism due to miscollimation. The technique is robust enough to collimate telescopes with fixed astigmatism in the telescope primary. (SECTION: Astronomical Instrumentation)

  15. Factors Influencing Efficacy of Peripheral Corneal Relaxing Incisions during Cataract Surgery

    PubMed Central

    Hirnschall, Nino; Wiesinger, Jörg; Draschl, Petra; Findl, Oliver

    2015-01-01

    Purpose. To evaluate influencing factors on the residual astigmatism after performing peripheral corneal relaxing incisions (PCRIs) during cataract surgery. Methods. This prospective study included patients who were scheduled for cataract surgery with PCRIs. Optical biometry (IOLMaster 500, Carl Zeiss Meditec AG, Germany) was taken preoperatively, 1 week, 4 months, and 1 year postoperatively. Additionally, corneal topography (Atlas model 9000, Carl Zeiss Meditec AG, Germany), ORA (Ocular Response Analyzer, Reichert Ophthalmic Instruments, USA), and autorefraction (Autorefractometer RM 8800 Topcon) were performed postoperatively. Results. Mean age of the study population (n = 74) was 73.5 years (±9.3; range: 53 to 90) and mean corneal astigmatism preoperatively was −1.82 D (±0.59; 1.00 to 4.50). Mean corneal astigmatism was reduced to 1.14 D (±0.67; 0.11 to 3.89) 4 months postoperatively. A partial least squares regression showed that a high eccentricity of the cornea, a large deviation between keratometry and topography, and a high preoperative astigmatism resulted in a larger postoperative error concerning astigmatism. Conclusions. PCRI causes a reduction of preoperative astigmatism, though the prediction is difficult but several factors were found to be a relevant source of error. PMID:26199739

  16. Resultant vertical prism in toric soft contact lenses.

    PubMed

    Sulley, Anna; Hawke, Ryan; Lorenz, Kathrine Osborn; Toubouti, Youssef; Olivares, Giovanna

    2015-08-01

    Rotational stability of toric soft contact lenses (TSCLs) is achieved using a range of designs. Designs utilising prism or peripheral ballast may result in residual prism in the optic zone. This study quantifies the vertical prism in the central 6mm present in TSCLs with various stabilisation methods. Vertical prism was computed using published refractive index and vertical thickness changes in the central optic zone on a full lens thickness map. Thickness maps were measured using scanning transmission microscopy. Designs tested were reusable, silicone hydrogel and hydrogel TSCLs: SofLens(®) Toric, PureVision(®)2 for Astigmatism, PureVision(®) Toric, Biofinity(®) Toric, Avaira(®) Toric, clariti(®) toric, AIR OPTIX(®) for ASTIGMATISM and ACUVUE OASYS(®) for ASTIGMATISM; with eight parameter combinations for each lens (-6.00DS to +3.00DS, -1.25DC, 90° and 180° axes). All TSCL designs evaluated had vertical prism in the optic zone except one which had virtually none (0.01Δ). Mean prism ranged from 0.52Δ to 1.15Δ, with three designs having prism that varied with sphere power. Vertical prism in ACUVUE OASYS(®) for ASTIGMATISM was significantly lower than all other TSCLs tested. TSCL designs utilising prism-ballast and peri-ballast for stabilisation have vertical prism in the central optic zone. In monocular astigmats fitted with a TSCL or those wearing a mix of toric designs, vertical prism imbalance could create or exacerbate disturbances in binocular vision function. Practitioners should be aware of this potential effect when selecting which TSCL designs to prescribe, particularly for monocular astigmats with pre-existing binocular vision anomalies, and when managing complaints of asthenopia in monocular astigmats. Copyright © 2015 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

  17. Shack-Hartmann sensor based optical quality testing of whole slide imaging systems for digital pathology

    NASA Astrophysics Data System (ADS)

    Shakeri, S. M.; Hulsken, Bas; van Vliet, Lucas J.; Stallinga, Sjoerd

    2015-03-01

    Whole Slide Imaging (WSI) systems are used in the emerging field of digital pathology for capturing high-resolution images of tissue slides at high throughput. We present a technique to measure the optical aberrations of WSI systems using a Shack-Hartmann wavefront sensor as a function of field position. The resulting full-field aberration maps for the lowest order astigmatism and coma are analyzed using nodal aberration theory. According to this theory two coefficients describe the astigmatism and coma inherent to the optical design and another six coefficients are needed to describe the cumulative effects of all possible misalignments on astigmatism and coma. The nodal aberration theory appears to fit well to the experimental data. We have measured and analyzed the full-field aberration maps for two different objective lens-tube lens assemblies and found that only the optical design related astigmatism coefficient differed substantially between the two cases, but in agreement with expectations. We have also studied full-field aberration maps for intentional decenter and tilt and found that these affect the misalignment coefficient for constant coma (decenter) and the misalignment coefficient for linear astigmatism (tilt), while keeping all other nodal aberration theory coefficients constant.

  18. [Pre- and postoperative corneal topography after combined single suture and running suture in ECCE. An analysis using the video keratoscope].

    PubMed

    Schickel, B; Holschbach, A; Strobel, J

    1993-12-01

    In a prospective study with 45 patients undergoing extracapsular cataract extraction (ECCE) with implantation of posterior chamber lens, curvature measurements of the cornea by means of computerized videokeratoscope were taken postoperatively. Analysis of the corneal shape on color-coded topographic maps of astigmatism showed an hourglass-shaped formation in all patients with a main axis in the sense of general astigmatism. Within a 3-mm zone (optical zone) the steepest meridian in all eyes was 96.1 +/- 13.3 degrees with an astigmatism of +4.4 +/- 2.1 D (1st postoperative day). Postoperatively we found that 35.6% of the patients examined had irregular astigmatism that could not be corroborated by the readings from the Javal ophthalmometer. An irregular astigmatism, corneal topographic analysis reveals regions peripheral to the center with a peak corneal refractive power of +43.8 +/- 1.4 D. In contrast to the conventional methods (for example, Javal ophthalmometer, autokeratometer), computerized videokeratoscope analysis provides additional and useful information on the corneal topography after intraocular operations.

  19. Effect of incision types for Artisan phakic intraocular lens implantation on ocular higher order aberrations

    PubMed Central

    Park, Young Min; Choi, Bong Joon; Lee, Jong Soo

    2016-01-01

    AIM To evaluate the effect of incision types for Artisan phakic intraocular lens (PIOL) implantation on ocular higher-order aberrations (HOAs). METHODS A retrospective review was conducted of the patients who had undergone Artisan PIOL implantation for the correction of myopia and followed up for at least 6mo. Patients are classified into 2 groups considering the incision type: cornea group with patients undergone clear corneal incision; sclera group with patients undergone sclera tunnel incision. All patients with postoperative astigmatism of under 1 diopter (D) were included to minimize the effect of residual astigmatism on postoperative HOAs. Visual acuity, special equivalents, astigmatism, predictability (±1 D from target refraction), HOAs (coma, trefoil, spherical aberration), and corneal endothelial counts were analyzed preoperatively and 6mo postoperatively. RESULTS At the postoperative 6mo, all patients of both groups achieved uncorrected visual acuity of 16/20 or better, and significantly decreased the spherical equivalents compared with preoperative values. The predictability of refractive correction was 96% in the former, and 94% in the latter. Unlike the sclera group, preoperative astigmatism decreased significantly in cornea group at postoperative 6mo. The HOAs increased significantly at postoperative 6mo compared to the preoperative values in both groups, and the root mean square (RMS) total and trefoil wavefront aberration of cornea group were significantly higher than those of sclera group. CONCLUSION Although corneal incision significantly reduces preexisting astigmatism, the postoperative 6mo of total RMS and trefoil aberration change may deteriorate the visual quality after Artisan PIOL implantation. PMID:28003980

  20. [ECCE with self-sealing cataract incision. Technique and clinical results].

    PubMed

    Pham, D T; Wollensak, J; Drosch, S

    1995-06-01

    We present of modified technique for sutureless ECCE with a trapezoidal tunnel incision of 11 mm. The operation can be performed in a closed system because of the self-sealing wound construction. Compared to the sutured corneoscleral ECCE the new procedure has important advantages: the procedure is safe even during the critical phase following nucleus extraction. The procedure is therefore safer, faster, more economical and suture-induced astigmatism is avoided. Clinical experience after 2 years showed that postoperative complications were reduced significantly. Iris prolapse, wound dehiscens and hyphema occurred at a rate of 2%. The astigmatism (Jaffe analysis) was at a rate of 2 D, stable within 4 weeks after surgery, and did not change up to 2 years postoperatively. The astigmatism induced was then reduced about 0.5 D by a radical suture.

  1. Optical design of systems with off-axis spherical mirrors

    NASA Astrophysics Data System (ADS)

    Malacara-Hernández, Daniel; Gomez-Vieyra, Armando

    2011-09-01

    The astigmatism in reflective imaging systems can be eliminated by a proper configuration. However, the spherical and coma are the main residual aberrations in third order theory, but the behavior of all aberrations is not yet fully The main aberration of classical off-axis reflecting systems is primary astigmatism. The astigmatism in off-axis spherical understood. Expressions for the wavefront aberrations in an off-axis spherical mirror are presented. These formulas are derived from the optical path difference between an ellipsoid and a sphere, assuming a relatively small pupil and a small angle of incidence as it will be described with detail. Using the principle of the optical path difference, we developed the mathematical expressions that describe the third order wavefront aberrations in a two spherical mirror system when the object is finite.

  2. Results of initial phase conjugation experiments in CS/sub 2/ and CCl/sub 4/

    SciTech Connect

    Milam, D.; Marshall, C.; Vercimak, C.; Moore, T.

    1988-05-17

    A liquid with lower nonlinear refractive index, CCl/sub 4/, provided conjugated beams with clean near field distribution, unless astigmatism was added to the input beam. Astigmatism caused fringing on the conjugated beam. The tendency toward fringing was diminished in our more recent experiments in glass and methane. Measured thresholds and reflectances for both CS/sub 2/ and CC1/sub 4/ agreed with published results. Waveforms of pulses produced by SBS are different from those of the input pulse. Except for tansients observed on the leading edge, all aspects of the SBS wave form can be explained. Correction by conjugation in CC1/sub 4/for up to 4.5 waves of astigmatism provided beams with divergence not greater than twice the diffraction limit. Experimental error may account for some of the apparent divergence. 12 refs., 12 figs.

  3. Focused high-intensity proton beam from a lithium source by using an E times B stigmatic selector

    SciTech Connect

    Leal-Quiros, E.; Prelas, M.A. )

    1990-01-01

    This article describes the design and operation of a system that produces a high-intensity proton beam. The system consists of a lithium proton source and an {bold E}{times}{bold B} stigmatic selector that produces a stigmatic proton beam at the mass focus. The protons are produced by bombarding electrons against a lithium surface. These protons are accelerated toward a special tilted-pole Wien filter (stigmatic selector), which eliminates astigmatism in the proton beam at the mass focus. The stigmatic {bold E}{times}{bold B} selector was also tested with electron beams, and their astigmatism was also eliminated. A classical {bold E}{times}{bold B} Wien filter with parallel poles (astigmatic selector) was used for comparison. The experimental spectral curves of both the proton current and the electron current, each using both types of selectors, are shown.

  4. Impact of Posterior Corneal Surface on Toric Intraocular Lens (IOL) Calculation.

    PubMed

    Preussner, Paul-Rolf; Hoffmann, Peter; Wahl, Jochen

    2015-01-01

    To quantify the impact of posterior cornea on toric IOL calculation accuracy using Placido-topography of anterior corneal surface and Scheimpflug measurements of corneal thickness. Three-hundred seventy-nine non-selected eyes undergoing cataract surgery with non-toric intraocular lens (IOL) implantation were measured with TMS-5 (Tomey, Japan), IOLMaster (Zeiss, Germany) and Lenstar (Haag-Streit, Switzerland). Anterior, posterior and total measured corneal astigmatisms were compared with astigmatisms from postoperative refraction by calculating vector differences. The average absolute vector difference between anterior astigmatism and total astigmatism combining the measurements of anterior and posterior cornea was only 0.3 ± 0.2 D, with a median of only 0.27 D, but a maximum of 1.5 D. Measurements of anterior cornea alone show a systematic difference from refractive cylinder of 0.3-6 D at 90, 0.38 D at 89° and 0.28 D at 91° (IOLMaster, Lenstar and anterior TMS5), whereas the total TMS5 cylinder differs on average by only 0.14D at 81° from the refractive cylinder. With-the-rule (WTR) corneal astigmatism is slightly reduced and against-the-rule (ATR) astigmatism slightly increased on average when posterior corneal surface is taken into account additionally. This could also be confirmed by the calculation of an average pachymetry of all eyes in which the thinnest central part shows an ellipsoidal shape with horizontally long axis. Measurements of posterior cornea have on average only a small but significant impact on the outcome of toric IOL calculation, however, they are nevertheless recommended to detect outliers in which corneal irregularities (e.g. beginning keratokonus) may be overlooked.

  5. Comparison of intraocular pressure measurement using 4 different instruments following penetrating keratoplasty.

    PubMed

    Chou, Chi-Ying; Jordan, Charlotte A; McGhee, Charles N J; Patel, Dipika V

    2012-03-01

    To compare intraocular pressure (IOP) measurements after penetrating keratoplasty (PK) using Goldmann applanation tonometry (GAT; Haag-Streit USA), TonoPen XL (Reichert Inc), Pascal Dynamic Contour tonometer (PDCT; Swiss Microtechnology AG), and Ocular Response Analyzer (ORA; Reichert Inc) and to analyze effects and correlation of corneal thickness and curvature on these measurements. Prospective, cross-sectional study. Departments of Ophthalmology, University of Auckland and Auckland District Health Board, New Zealand. Thirty-one eyes of 31 participants with previous PK. IOP measured using GAT, TonoPen, PDCT, and ORA. Central corneal thickness (CCT) and corneal astigmatism were assessed by Pentacam rotating Scheimpflug tomography. Degree of agreement in IOP measures and correlation with CCT and corneal astigmatism. Mean age was 44.5 ± 21.0 years and mean time since PK was 27.7 ± 28.2 months (range 3.0-122.4 months). Mean CCT was 585 ± 149 μm and mean corneal astigmatism 5.5 ± 3.8 diopters. There was no significant difference in IOP measured by GAT and TonoPen; however, both PDCT (2.12 mm Hg, P < .01) and ORA (6.29 mm Hg, P < .01) measured significantly higher IOPs compared to GAT. ORA showed the least agreement with GAT. Significant correlation was identified between each pair of measurement techniques. No instruments correlated significantly with CCT. Only PDCT showed no significant correlation with corneal astigmatism. However, no IOP measures correlated with corneal astigmatism if sutures in situ or less than 1 year post-PK. TonoPen or PDCT are the most suitable alternatives for measuring IOP in PK eyes where GAT readings are difficult to obtain. PDCT also offers the advantage of being independent of both CCT and corneal astigmatism. Copyright © 2012 Elsevier Inc. All rights reserved.

  6. Unveiling orbital angular momentum and acceleration of light beams and electron beams

    NASA Astrophysics Data System (ADS)

    Arie, Ady

    Special beams, such as the vortex beams that carry orbital angular momentum (OAM) and the Airy beam that preserves its shape while propagating along parabolic trajectory, have drawn significant attention recently both in light optics and in electron optics experiments. In order to utilize these beams, simple methods are needed that enable to easily quantify their defining properties, namely the OAM for the vortex beams and the nodal trajectory acceleration coefficient for the Airy beam. Here we demonstrate a straightforward method to determine these quantities by astigmatic Fourier transform of the beam. For electron beams in a transmission electron microscope, this transformation is easily realized using the condenser and objective stigmators, whereas for light beam this can be achieved using a cylindrical lens. In the case of Laguerre-Gauss vortex beams, it is already well known that applying the astigmatic Fourier transformation converts them to Hermite-Gauss beams. The topological charge (and hence the OAM) can be determined by simply counting the number of dark stripes of the Hermite-Gauss beam. We generated a series of electron vortex beams and managed to determine the topological charge up to a value of 10. The same concept of astigmatic transformation was then used to unveil the acceleration of an electron Airy beam. The shape of astigmatic-transformed depends only on the astigmatic measure and on the acceleration coefficient. This method was experimentally verified by generating electron Airy beams with different known acceleration parameters, enabling direct comparison to the deduced values from the astigmatic transformation measurements. The method can be extended to other types of waves. Specifically, we have recently used it to determine the acceleration of an optical Airy beams and the topological charge of so-called Airy-vortex light beam, i.e. an Airy light beam with an embedded vortex. This work was supported by DIP and the Israel Science

  7. Symbolic algebra approach to the calculation of intraocular lens power following cataract surgery

    NASA Astrophysics Data System (ADS)

    Hjelmstad, David P.; Sayegh, Samir I.

    2013-03-01

    We present a symbolic approach based on matrix methods that allows for the analysis and computation of intraocular lens power following cataract surgery. We extend the basic matrix approach corresponding to paraxial optics to include astigmatism and other aberrations. The symbolic approach allows for a refined analysis of the potential sources of errors ("refractive surprises"). We demonstrate the computation of lens powers including toric lenses that correct for both defocus (myopia, hyperopia) and astigmatism. A specific implementation in Mathematica allows an elegant and powerful method for the design and analysis of these intraocular lenses.

  8. Modes of a twisted optical cavity

    SciTech Connect

    Habraken, Steven J. M.; Nienhuis, Gerard

    2007-03-15

    An astigmatic optical resonator consists of two astigmatic mirrors facing each other. The resonator is twisted when the symmetry axes of the mirrors are nonparallel. We present an algebraic method to obtain the complete set of the paraxial eigenmodes of such a resonator. Basic ingredients are the complex eigenvectors of the four-dimensional transfer matrix that describes the transformation of a ray of light over a roundtrip of the resonator. The relation between the fundamental mode and the higher-order modes is expressed in terms of raising operators in the spirit of the ladder operators of the quantum harmonic oscillator.

  9. Design Rules For Holographic Optical Scanning Elements

    NASA Astrophysics Data System (ADS)

    Herzig, H. P.; Dandliker, R.

    1987-10-01

    An analytical method for the design of holographic optical elements (HOE) for focussing laser scanners with minimum aberrations and optimum scan line definition is reported. It can be shown analytically, using second order (paraxial) approximation, that a circular motion of the HOE cannot generate a straight line in space without astigmatism of the focal spot. Accepting a slightly curved scan line, the astigmatism can be compensated. Experimental results for HOE with a wavelength shift between recording and reconstruction are demonstrated. The required aspherical wavefronts for the recording are realized with the help of computer generated holograms (CGH).

  10. Wound construction in manual small incision cataract surgery

    PubMed Central

    Haldipurkar, S S; Shikari, Hasanain T; Gokhale, Vishwanath

    2009-01-01

    The basis of manual small incision cataract surgery is the tunnel construction for entry to the anterior chamber. The parameters important for the structural integrity of the tunnel are the self-sealing property of the tunnel, the location of the wound on the sclera with respect to the limbus, and the shape of the wound. Cataract surgery has gone beyond just being a means to get the lens out of the eye. Postoperative astigmatism plays an important role in the evaluation of final outcome of surgery. Astigmatic consideration, hence, forms an integral part of incisional considerations prior to surgery. PMID:19075401

  11. Thermal lens shaping for stigmatic Brewster-cut diode-pumped solid-state lasers

    NASA Astrophysics Data System (ADS)

    Rimington, Nathan

    By combining an elliptical-shaped diode laser pump spot with the one-dimensional heat flow in a laser slab, the thermal lens can be shaped to compensate for astigmatism. The intrinsic astigmatism in a Brewster slab was compensated for in two different laser crystals---Nd:YAG and Nd:GdVO4---using this thermal lens-shaping technique. The modeling of the lens allowed the estimation of the thermo-optic coefficient of Nd:GdVO4, and it was found to be 4 (+/-1) x 10-6/K.

  12. Adjustable fluidic lenses for ophthalmic corrections.

    PubMed

    Marks, Randall; Mathine, David L; Peyman, Gholam; Schwiegerling, Jim; Peyghambarian, Nasser

    2009-02-15

    We report on two fluidic lenses that have been developed for ophthalmic applications. The lenses use a circular aperture to demonstrate optical powers between -20 and +20 D and a rectangular aperture to demonstrate astigmatism with values ranging from 0 to 8 D. Measurements of image quality were made with the fluidic lens using a model eye. Both lenses were variable and controllable by adjusting the fluid volume of the lens. To the best of our knowledge this is the first demonstration of a continuously variable lens for control of astigmatism.

  13. Link between diffraction losses and light beam cross section in laser with telescopic resonator

    SciTech Connect

    Dmitriev, A.K.; Nekrasov, Yu.V.

    1987-06-01

    The light beam cross section change in a laser and its link with the diffraction losses during the telescopic converter defocusing is discussed. In addition, the measurements of the resonator astigmatism compensation by the Brewster window are carried out. It is demonstrated that in the resonator stability region, the light beam cross section is well described by the expression using the transmission matrix elements, the simplified model for the diffraction qualitatively correlates with the test data, and the mirror astigmatism due to the inclined light beam incidence is compensated for by Brewster's window.

  14. Diffraction analysis and evaluation of several focus- and track-error detection schemes for magneto-optical disk systems

    NASA Technical Reports Server (NTRS)

    Bernacki, Bruce E.; Mansuripur, M.

    1992-01-01

    A commonly used tracking method on pre-grooved magneto-optical (MO) media is the push-pull technique, and the astigmatic method is a popular focus-error detection approach. These two methods are analyzed using DIFFRACT, a general-purpose scalar diffraction modeling program, to observe the effects on the error signals due to focusing lens misalignment, Seidel aberrations, and optical crosstalk (feedthrough) between the focusing and tracking servos. Using the results of the astigmatic/push-pull system as a basis for comparison, a novel focus/track-error detection technique that utilizes a ring toric lens is evaluated as well as the obscuration method (focus error detection only).

  15. Pinhole Glasses

    ERIC Educational Resources Information Center

    Colicchia, Giuseppe; Hopf, Martin; Wiesner, Hartmut; Zollman, Dean

    2008-01-01

    Eye aberrations are commonly corrected by lenses that restore vision by altering rays before they pass through the cornea. Some modern promoters claim that pinhole glasses are better than conventional lenses in correcting all kinds of refractive defects such as myopia (nearsighted), hyperopia (farsighted), astigmatisms, and presbyopia. Do pinhole…

  16. Tscherning ellipses and ray tracing in ophthalmic lenses.

    PubMed

    Malacara, Z; Malacara, D

    1985-07-01

    In this paper the exact shape of the solutions to the equations for lenses free of oblique astigmatism, as well as those free from curvature of field or peripheral focus error, are presented. These solutions, as expected, resemble the Tscherning ellipses, but strongly deformed.

  17. Laser-induced scleral shrinkage for refractive surgery

    NASA Astrophysics Data System (ADS)

    Ren, Qiushi; Simon, Gabriel; Parel, Jean-Marie A.; Shen, Jin-Hui

    1994-06-01

    We investigate the laser refractive scleroplasty (LRS) as a potential minimal-invasive method for correcting post-operative astigmatism. The scleral shrinkage near limbus was induced on 6 cadaver eyes using a 200 micrometers fiber optic probe coupled to a pulsed Ho:YAG laser. The diameter of the treatment spot was 0.8 mm. The output energy measured at tip was 60.2+/- 0.6 mJ. The treatments consisted of multiple sector patterns placed along the major axis of astigmatism parallel to the limbus, and round patterns placed along the limbus. Three treatment spots were applied on each side of the sector. The separation among sectors and limbus is 1 mm. Keratometry and topography of the cornea were measured after each sector or round pattern treatment. Effect of 5 and 10 pulses at each treatment spot were compared. Histology was performed to evaluate laser tissue damage. The major axis of astigmatism was shifted 90 degrees after the sector pattern treatment and amount of dioptric change increased when adding a new treatment or using more treatment pulses. However, the spherical equivalent of the eyes was essentially unchanged. The keratometry of the corneas remained the same after the round pattern treatment. Laser refractive scleroplasty may be applied for the correction of post-operative astigmatism.

  18. VISUAL DEFICIENCIES AND READING DISABILITY.

    ERIC Educational Resources Information Center

    ROSEN, CARL L.

    THE ROLE OF VISUAL SENSORY DEFICIENCIES IN THE CAUSATION READING DISABILITY IS DISCUSSED. PREVIOUS AND CURRENT RESEARCH STUDIES DEALING WITH SPECIFIC VISUAL PROBLEMS WHICH HAVE BEEN FOUND TO BE NEGATIVELY RELATED TO SUCCESSFUL READING ACHIEVEMENT ARE LISTED--(1) FARSIGHTEDNESS, (2) ASTIGMATISM, (3) BINOCULAR INCOORDINATIONS, AND (4) FUSIONAL…

  19. Acquisition, Image and Data Compression.

    DTIC Science & Technology

    1983-04-30

    ELECTRICAL ENGINEERING COMM’, UNICATIONS SYSTEMS LABORATORY ~V 7 SECURITY CLASSIFICATION OF THIS PAGE (When Des Ftered) REPORT DOCUMENTATION PAGE...Lusing an astigmatic processor.2,5 Or one can use a 2-D multiplexed holographic processor to implement di- rectly the space-variant impulse response

  20. Pseudophakic eye with obliquely crossed piggyback toric intraocular lenses.

    PubMed

    Jin, Haiying; Limberger, Il-Joo; Borkenstein, Andreas F M; Ehmer, Angela; Guo, Haike; Auffarth, Gerd U

    2010-03-01

    A 72-year-old man presented with high astigmatism (2.25 -5.0 x 45) induced by long-term rotation of a toric intraocular lens (IOL). Corneal astigmatism was 3.78 diopters (D). The corrected distance visual acuity (CDVA) was 20/32. Because of the risk of repositioning, a secondary toric IOL of -3.0/6.0 D especially designed for sulcus implantation was piggybacked through 3.5 mm sutureless clear-corneal incision with a cylindrical axis obliquely crossed with that of the primary IOL. Eight months postoperatively, the corneal astigmatism was 5.04 D. The CDVA was 20/25 with a refraction of 1.0 -2.5 x 70. No interlenticular opacification or significant rotation or decentration of the secondary toric IOL was observed. The refractive properties of this pseudophakic eye were analyzed using a mathematical approach. The calculated postoperative refraction was 0.84 -1.7 x 47. A piggyback toric IOL can be implanted in an obliquely crossed style that allows a secondary toric IOL to correct astigmatism induced by long-term toric IOL rotation. Copyright 2010 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

  1. Alignment and assembly process for primary mirror subsystem of a spaceborne telescope

    NASA Astrophysics Data System (ADS)

    Lin, Wei-Cheng; Chang, Shenq-Tsong; Chang, Sheng-Hsiung; Chang, Chen-Peng; Lin, Yu-Chuan; Chin, Chi-Chieh; Pan, Hsu-Pin; Huang, Ting-Ming

    2015-11-01

    In this study, a multispectral spaceborne Cassegrain telescope was developed. The telescope was equipped with a primary mirror with a 450-mm clear aperture composed of Zerodur and lightweighted at a ratio of approximately 50% to meet both thermal and mass requirements. Reducing the astigmatism was critical for this mirror. The astigmatism is caused by gravity effects, the bonding process, and deformation from mounting the main structure of the telescope (main plate). This article presents the primary mirror alignment, mechanical ground-supported equipment (MGSE), assembly process, and optical performance test used to assemble the primary mirror. A mechanical compensated shim is used as the interface between the bipod flexure and main plate. The shim was used to compensate for manufacturer errors found in components and differences between local coplanarity errors to prevent stress while the bipod flexure was screwed to the main plate. After primary mirror assembly, an optical performance test method called a bench test with an algorithm was used to analyze the astigmatism caused by the gravity effect and deformation from the mounting or supporter. The tolerance conditions for the primary mirror assembly require the astigmatism caused by gravity and mounting force deformation to be less than P-V 0.02 λ at 632.8 nm. The results demonstrated that the designed MGSE used in the alignment and assembly processes met the critical requirements for the primary mirror assembly of the telescope.

  2. Utility of an open field Shack-Hartmann aberrometer for measurement of refractive error in infants and young children

    PubMed Central

    Harvey, Erin M.; Miller, Joseph M.; Schwiegerling, Jim

    2013-01-01

    PURPOSE To assess the utility of an open-field Shack-Hartmann aberrometer for measurement of refractive error without cycloplegia in infants and young children. METHOD Data included 2698 subject encounters with Native American infants and children aged 6 months to <8 years. We attempted right eye measurements without cycloplegia using the pediatric wavefront evaluator (PeWE) on all participants while they viewed near (50 cm) and distant (2 m) fixation targets. Cycloplegic autorefraction (Rmax [Nikon Retinomax K-plus2]) measurements were obtained for children aged ≥3 years. RESULTS The success rates of noncycloplegic PeWE measurement for near (70%) and distant targets (56%) significantly improved with age. Significant differences in mean spherical equivalent (M) across near versus distant fixation target conditions were consistent with the difference in accommodative demand. Differences in astigmatism measurements for near versus distant target conditions were not clinically significant. Noncycloplegic PeWE and cycloplegic Rmax measurements of M and astigmatism were strongly correlated. Mean noncycloplegic PeWE M was significantly more myopic or less hyperopic and astigmatism measurements tended to be greater in magnitude compared with cycloplegic Rmax. CONCLUSIONS The PeWE tended to overestimate myopia and underestimate hyperopia when cycloplegia was not used. The PeWE is useful for measuring accommodation and astigmatism. PMID:24160970

  3. Airy, Sir George Biddell (1801-92)

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    A brilliant Cambridge mathematician (Senior Wrangler 1823, i.e. leader of the graduating mathematics class), Airy became the seventh Astronomer Royal in 1835 after a brief period as Lucasian Professor at Cambridge. His output was prodigious, and he published nearly 400 scientific papers and 150 reports on various scientific issues, such as the gauge of railways, spectacles to correct astigmatism,...

  4. New optical mountings of the spectral devices with concave diffraction gratings and high entrance slit

    NASA Astrophysics Data System (ADS)

    Sokolova, Elena A.; Reyes Cortes, Santiago D.

    1996-11-01

    The concave diffraction grating is both the dispersive and the focusing element at the same time. It can be the only optical unit of monochromator or polychromator. Using the concave diffraction gratings with nonequidistant and curved grooves gives the possibility for correction of the aberrations in the useful region of spectrum and provides the devices with determined focal surfaces. To increase the height of the entrance slit of the spectroscopic device we have to eliminate the first and the second-order astigmatism aberrations. Consideration of this type of aberration is very important now in view of the new types of spectral devices using fiber optics and multielement detectors being developed. These new elements allow us to register the spectrum of extended objects or a number of spectrums simultaneously. For the case of the double monochromator we noticed, that the second-order astigmatism can be completely eliminated if the second part of the double monochromator is equivalent to its first part, but the ray tracing is inverse. The experiment on the mathematical model of the double monochromator confirms this idea. For the case of polychromator or CCD spectrometer we can compensate that aberrations using the illumination system, consists of the spherical mirror. The angle of incidence of the light to the mirror is calculated such a way, that the astigmatism of the grating is compensated by the astigmatism of the mirror.

  5. Advances in femtosecond laser technology

    PubMed Central

    Callou, Thais Pinheiro; Garcia, Renato; Mukai, Adriana; Giacomin, Natalia T; de Souza, Rodrigo Guimarães; Bechara, Samir J

    2016-01-01

    Femtosecond laser technology has become widely adopted by ophthalmic surgeons. The purpose of this study is to discuss applications and advantages of femtosecond lasers over traditional manual techniques, and related unique complications in cataract surgery and corneal refractive surgical procedures, including: LASIK flap creation, intracorneal ring segment implantation, presbyopic treatments, keratoplasty, astigmatic keratotomy, and intrastromal lenticule procedures. PMID:27143847

  6. RESONATORS, MODES, BEAMS: Gain saturation of laser beams and production and decay of phase dislocations

    NASA Astrophysics Data System (ADS)

    Malyutin, A. A.

    2006-02-01

    The distortion of the distribution of initially pure laser modes caused by the gain saturation is simulated numerically. It is shown that the gain saturation results in a considerable enrichment of the modal spectrum of radiation accompanied by the production and decay of phase dislocations in the far-field domain and at the output of an astigmatic π/2-mode converter.

  7. LASER BEAMS: Rotation of arbitrary laser beams using π/2-mode converters

    NASA Astrophysics Data System (ADS)

    Malyutin, A. A.

    2003-03-01

    Two types of rotators of arbitrary beams based on astigmatic π/2 and π converters of laser modes are described. Unlike traditional rotators of Dove prism type, proposed schemes use exclusively refracting optical components. Numerical simulations of the beam rotators are performed based both on Fresnel theory and ray-tracing method.

  8. Corneal Topographic Changes After Eyelid Ptosis Surgery.

    PubMed

    Savino, Gustavo; Battendieri, Remo; Riso, Monica; Traina, Salvatore; Poscia, Andrea; DʼAmico, Giovanni; Caporossi, Aldo

    2016-04-01

    To evaluate the corneal topography and the topographic changes after ptosis surgery on patients affected by congenital and acquired blepharoptosis. Twenty eyes of 17 patients affected by acquired and congenital ptosis underwent surgical correction through anterior levator complex tightening. Computerized tomography (Syrius Sistem; CSO) was used to analyze any change in corneal astigmatism (CYL), simulated keratometry, anterior corneal symmetry index front, apical keratometry front, and central corneal thickness. Visual acuity, margin reflex distance, and levator function were also measured. After surgical ptosis repair, corneal topography demonstrated a reduction in average keratometry of 0.15 ± 0.47 diopters (D) and in corneal astigmatism of 0.26 ± 1.12 D. Significant differences were found in apical keratometry front (-1.84 ± 1.76 D) and in best-corrected visual acuity (-0.18 ± 0.06 logMAR) in the postoperative examinations. Central corneal thickness did not show significant differences between preoperative and postoperative examinations. Postoperative topographic maps showed a reduction of symmetry index front (0.10 ± 0.64 D). Eyelid ptosis modifies anterior corneal surface inducing refractive errors and modifying corneal astigmatism in patients, thus affecting the quality of vision. The surgical correction of blepharoptosis induces anterior corneal surface modification, restoring corneal symmetry and regular corneal astigmatism. Postoperative corneal topography showed normal corneal contours.

  9. In vivo and in vitro analysis of topographic changes secondary to DSAEK venting incisions

    PubMed Central

    Moshirfar, Majid; Lependu, Monette T; Church, Dane; Neuffer, Marcus C

    2011-01-01

    Introduction Descemet’s stripping automated endothelial keratoplasty (DSAEK) venting incisions may induce irregular corneal astigmatism. The study examines in vivo and in vitro astigmatic effects of venting incisions. Patients and methods In vivo analysis examined eleven eyes of eleven patients who had received DSAEK with venting incisions. A chart review of the eleven eyes including assessment of pre and postoperative refraction and topography was performed. In vitro analysis examined three cadaver eyes which received topographic imaging followed by venting incisions at 4 mm, 6 mm, and 7 mm optical zones. Topographic imaging was then performed again after the incisions. Results Postoperative topographies of eleven eyes demonstrated localized flattening at incision sites and cloverleaf pattern astigmatism. There was a significant difference in corneal irregularity measurement (P = 0.03), but no significant difference in shape factor or change of topographic cylinder. The cloverleaf pattern was found in cadaver eyes with incisions placed at 4 mm and 6 mm optical zones but not at the 7 mm zone. Conclusion DSAEK venting incisions can cause irregular corneal astigmatism that may affect visual outcomes. The authors recommend placement of venting incisions near the 7 mm optical zone. PMID:21966185

  10. In vivo and in vitro analysis of topographic changes secondary to DSAEK venting incisions.

    PubMed

    Moshirfar, Majid; Lependu, Monette T; Church, Dane; Neuffer, Marcus C

    2011-01-01

    Descemet's stripping automated endothelial keratoplasty (DSAEK) venting incisions may induce irregular corneal astigmatism. The study examines in vivo and in vitro astigmatic effects of venting incisions. In vivo analysis examined eleven eyes of eleven patients who had received DSAEK with venting incisions. A chart review of the eleven eyes including assessment of pre and postoperative refraction and topography was performed. In vitro analysis examined three cadaver eyes which received topographic imaging followed by venting incisions at 4 mm, 6 mm, and 7 mm optical zones. Topographic imaging was then performed again after the incisions. Postoperative topographies of eleven eyes demonstrated localized flattening at incision sites and cloverleaf pattern astigmatism. There was a significant difference in corneal irregularity measurement (P = 0.03), but no significant difference in shape factor or change of topographic cylinder. The cloverleaf pattern was found in cadaver eyes with incisions placed at 4 mm and 6 mm optical zones but not at the 7 mm zone. DSAEK venting incisions can cause irregular corneal astigmatism that may affect visual outcomes. The authors recommend placement of venting incisions near the 7 mm optical zone.

  11. Implantation of Artisan toric phakic intraocular lens following Intacs in a patient with keratoconus.

    PubMed

    Kamburoğlu, Günhal; Ertan, Aylin; Bahadir, Mehmet

    2007-03-01

    We report a 24-year-old man with bilateral keratoconus in whom Intacs (Addition Technology, Inc.) were implanted in both eyes. The procedure was followed by Artisan toric phakic intraocular lens (Ophtec) implantation to correct the residual myopic and astigmatic refractive error.

  12. Tetravalent Chromium (Cr(4+)) as Laser-Active Ion for Tunable Solid-State Lasers

    NASA Technical Reports Server (NTRS)

    Seas, A.; Petricevic, V.; Alfano, Robert R.

    1992-01-01

    During 10/31/91 - 3/31/92, the following summarizes are major accomplishments: (1) numerical modeling of the four mirror astigmatically compensated, Z-fold cavity was performed; and (2) the simulation revealed several design parameters to be used for the construction of a femtosecond forsterite laser.

  13. Dipole azimuthons and vortex charge flipping in nematic liquid crystals.

    PubMed

    Izdebskaya, Yana V; Desyatnikov, Anton S; Assanto, Gaetano; Kivshar, Yuri S

    2011-10-24

    We demonstrate self-trapped laser beams carrying phase singularities in nematic liquid crystals. We experimentally observe the astigmatic transformation of vortex beams into spiraling dipole azimuthons accompanied by power-dependent charge-flipping of the on-axis phase singularity. The latter topological reactions involve triplets of vortex lines and resemble pitchfork bifurcations. © 2011 Optical Society of America

  14. [Calculations of mean refraction and variation of refraction using a dioptric space].

    PubMed

    Touzeau, O; Costantini, E; Gaujoux, T; Borderie, V; Laroche, L

    2010-11-01

    Polar notations (sphere, cylinder, and axis) of refraction perfectly characterize a single refraction but are not suitable for statistical analysis or graphic representation. While the spherical component of refraction can be easily analyzed by the spherical equivalent, statistical analysis of astigmatism requires non-polar expressions of refraction. Indeed, the cylinder and axis of astigmatism are not independent data. In addition, axis is a directional data including a non-trigonometric cycle. Refraction can be written in a non-polar notation by three rectangular coordinates (x, y, z), which can also represent the spherocylinder by one point in a dioptric space. These three coordinates constitute three independent (orthogonal) variables that correspond to a sphere-equivalent component and a pair of Jackson cross-cylinder components, oriented at 0°/90° (WTR/ATR astigmatism) and 45°/135° (oblique astigmatism). Statistical analysis and graphical representation become less complicated when using rectangular coordinates of refraction. Rectangular coordinates of the mean refraction are obtained by average rectangular coordinates. Similarly, rectangular coordinates of refraction change are obtained by a single subtraction of rectangular coordinates between the final and initial refractions. After statistical analysis, the rectangular coordinates obtained can be converted into a polar form for a more easily understood result. Finally, non-polar notations includ