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Journal ArticleDOI

Correcting astigmatism with toric intraocular lenses: Effect of posterior corneal astigmatism

01 Dec 2013-Journal of Cataract and Refractive Surgery (Elsevier)-Vol. 39, Iss: 12, pp 1803-1809
TL;DR: Corneal astigmatism was overestimated in WTR by all devices and underestimated in ATR by all except the Placido–dual Scheimpflug analyzer.
Abstract: Purpose To evaluate the impact of posterior corneal astigmatism on outcomes with toric intraocular lenses (IOLs). Setting Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Design Case series. Methods Corneal astigmatism was measured using 5 devices before and 3 weeks after cataract surgery. Toric IOL alignment was recorded at surgery and at the slitlamp 3 weeks postoperatively. The actual corneal astigmatism was calculated based on refractive astigmatism 3 weeks postoperatively and the effective toric power calculated with the Holladay 2 formula. The prediction error was calculated as the difference between the astigmatism measured by each device and the actual corneal astigmatism. Vector analysis was used in all calculations. Results With the IOLMaster, Lenstar, Atlas, manual keratometer, and Galilei (combined Placido–dual Scheimpflug analyzer), the mean prediction errors (D) were, respectively, 0.59 @ 89.7, 0.48 @ 91.2, 0.51 @ 78.7, 0.62 @ 97.2, and 0.57 @ 93.9 for with-the-rule (WTR) astigmatism (60 to 120 degrees), and 0.17 @ 86.2, 0.23 @ 77.7, 0.23 @ 91.4, 0.41 @ 58.4, and 0.12 @ 7.3 for against-the-rule (ATR) astigmatism (0 to 30 degrees and 150 to 180 degrees). In the WTR eyes, there were significant WTR prediction errors (0.5 to 0.6 diopters [D]) by all devices. In ATR eyes, WTR prediction errors were 0.2 to 0.3 D by all devices except the Placido–dual Scheimpflug analyzer (all P Conclusions Corneal astigmatism was overestimated in WTR by all devices and underestimated in ATR by all except the Placido–dual Scheimpflug analyzer. A new toric IOL nomogram is proposed. Financial Disclosure Drs. Koch, Weikert, and Wang received research support from Ziemer USA, Inc. Dr. Koch has a financial interest with Alcon Laboratories, Inc., Abbott Medical Optics, Inc., Optimedica Corp., and Ziemer USA, Inc. No other author has a financial or proprietary interest in any material or method mentioned.
Citations
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Journal ArticleDOI
TL;DR: The purpose of this editorial is to provide guidance to prospective authors conducting precision studies in terms of basic concepts, terminology, statistical methods, sample size considerations, study design, use of 1 eye or 2 eyes, and worked examples.
Abstract: Ophthalmology is a technologically advancing field with the constant production of new instrumentation. Instruments are usually released on the market with manufacturers claiming performance in various data formats, and this is typically followed by clinical evaluation studies by independent users. Ubiquitous issues in this area include, not least, the variety of methods, both practically and statistically, and the various terminology differences. It is becoming exceedingly difficult for clinicians and researchers to make sense of study results that have used nonstandard methodology in addition to confounding terminology. Terms such as consistency, precision, reliability, accuracy, repeatability, reproducibility, and agreement are just some examples of the many terms that frequently appear in the ophthalmic literature with inconsistent definitions and synonymous usage. The purpose of this editorial is to provide guidance to prospective authors conducting precision (repeatability and reproducibility) studies in terms of basic concepts, terminology, statistical methods, sample size considerations, study design, use of 1 eye or 2 eyes, and worked examples. A number of bodies in the scientific world have devised their own terminology and statistical recommendations, some of which are similar and others markedly different. An example is the International Organization for Standardization (ISO), an independent nongovernmental membership organization and the world's largest developer of voluntary International Standards. ISO has published more than 20 500 International Standards covering almost every industry, including ophthalmology. Examples include standards relating to contact lenses, contact lens care products, intraocular lenses, intraocular implants, spectacle lenses, and ophthalmic instruments. The ISO standardsmight differ markedly even within ophthalmic instruments, an example being differing statistical methods for tonometry and topography. A full list is available on the ISOwebsite (www.iso.org). Such ISO standards are developed by following a formal methodology involving a multi-stakeholder process. They are organic and dynamic, and developments might take years. This editorial is not set to replace any of the ISO standards or suggest that a single approach should be applied to every situation but rather provides a practical commentary on precision that draws

147 citations

Journal ArticleDOI
TL;DR: Posterior corneal astigmatism exerts the highest influence on the ERA after toric IOL implantation, and basing calculations on total cornealeastigmatism rather than keratometricAstigmatic data were vectorially described by meridional and torsional powers, which improves the prediction of the residual refractiveAstigmatism.
Abstract: PURPOSE 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. METHODS 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. RESULTS 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. CONCLUSIONS 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.

130 citations


Cites result from "Correcting astigmatism with toric i..."

  • ...Our data show a partial discrepancy with those of a similar study comparing toric IOL outcomes as predicted by KA and TCA.(21) The authors, in fact, found that TCA improved astigmatism prediction only in ATR eyes....

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  • ...Moreover, the repeatability of posterior corneal curvature by Scheimpflug cameras has been shown to be lower than that for anterior corneal curvature.20 Our data show a partial discrepancy with those of a similar study comparing toric IOL outcomes as predicted by KA and TCA.21 The authors, in fact, found that TCA improved astigmatism prediction only in ATR eyes....

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Journal ArticleDOI
TL;DR: Comparing the accuracy of different methods that consider posterior corneal curvature in toric intraocular lens (IOL) calculations found that Residual astigmatism after toric IOL implantation can be reduced by appropriate consideration of the posterior cornea.
Abstract: Purpose To compare the accuracy of different methods that consider posterior corneal curvature in toric intraocular lens (IOL) calculations. Setting Ein-Tal Eye Center, Tel-Aviv, Israel. Design Retrospective comparative case series. Methods Consecutive cases of toric IOL implantation and preoperative measurements by optical biometry with optical low-coherence reflectometry (OLCR) (Lenstar LS 900) and a Scheimpflug camera (Pentacam) were retrospectively reviewed. Five methods of toric IOL calculation were compared as follows: (1) anterior corneal astigmatism using OLCR, (2) application of the Baylor nomogram, (3) posterior tomography combined with anterior corneal measurements using vector summation, (4) the Scheimpflug camera's true net power, and (5) total corneal refractive power. Toric IOL astigmatic power and axis, aiming for the lowest residual astigmatism, were selected according to these methods. Simulated residual refraction was calculated for each method based on manifest refraction and measured IOL alignment more than 3 weeks after surgery. Results The study included 115 eyes of 92 patients. The median simulated residual astigmatism was lower when based on vector summation of anterior and posterior astigmatisms than with calculations based on anterior corneal measurements only, application of the Baylor nomogram, true net power, and total corneal refractive power readings (0.49 diopters [D] versus 0.70 D, 0.60 D, 0.64 D, and 0.76 D, respectively) (P Conclusions Residual astigmatism after toric IOL implantation can be reduced by appropriate consideration of the posterior corneal astigmatism. Using methods that take into account the effect of the posterior cornea in toric IOL calculations is suggested. Financial Disclosures Drs. Assia and Kleinmann are consultants to Hanita Lenses, Israel. Dr. Abulafia received a speaker's fee from Haag-Streit AG. No other author has a financial or proprietary interest in any material or method mentioned.

96 citations


Cites background from "Correcting astigmatism with toric i..."

  • ...Using the recommended 5 scans, this device provides keratometry (K) readings based on 640 reference points.6 Similar to most standard keratometry and topography devices, corneal power is estimated according to anterior corneal curvature measurements with a keratometric index of 1.3375.7 http://dx.doi.org/10.1016/j.jcrs.2015.11.036 217 0886-3350 Recent studies have suggested that the posterior corneal surface also contributes to total corneal astigmatism.7–13 Koch et al.9 proposed that the effect of the posterior cornea astigmatism power in toric IOL selection should be taken into account, and they developed the Baylor toric nomogram as a solution....

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  • ...4 diopter (D).(9) However, the role of the posterior cornea in determining the IOL axis alignment was not addressed....

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  • ...The following methods of calculating preoperative corneal astigmatism and toric IOLs were compared: (1) anterior corneal measurements with the OLCR device, (2) application of the Baylor toric nomogram for the adjustment of posterior astigmatism power as described by Koch et al.,9 (3) integration of posterior corneal surface astigmatism measured by the Scheimpflug camera with the anterior corneal astigmatism measured by the OLCR device using vector summation (vector analysis) as described byHolladay et al.,15,16 (4) Scheimpflug camera–derived true net power calculated by the device using the radii of the anterior and posterior corneal curvatures, and (5) total corneal refractive power calculated using ray tracing by the Scheimpflug camera....

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  • ...Koch et al.(9) proposed that the effect of the posterior cornea astigmatism power in toric IOL selection should be taken into account, and they developed the Baylor toric nomogram as a solution....

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  • ...Koch et al.7 reported that anterior corneal measurements underestimated total corneal astigmatism by a mean vector of 0.22 D. Savini and Næser12 recently found a reduction in the error of refractive astigmatism ranging from 0.25 D (ATR) to 0.46 D (WTR) when total corneal astigmatism was used instead of anterior keratometric astigmatism....

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Journal ArticleDOI
TL;DR: Prediction of astigmatic outcomes with toric IOLs can be improved with appropriate measuring devices and methods to establish the required torica IOL power.
Abstract: Purpose To evaluate and compare the accuracy of different methods to measure and predict postoperative astigmatism with toric intraocular lens (IOL) implantation. Setting Ein-Tal Ophthalmology Center, Tel-Aviv, Israel. Design Retrospective case series. Methods Postoperative corneal astigmatism was measured with 3 devices (IOLMaster 500; optical low-coherence reflectometry [OLCR]–based Lenstar LS 900; Atlas topographer) and compared with the manifest astigmatic refractive outcome in patients with toric IOLs. The error in the predicted residual astigmatism was calculated by vector analysis according to the measurement and calculation method used to predict the required toric IOL cylinder power. Results The centroid errors in predicted residual astigmatism were against the rule with the Alcon and Holladay toric calculators (0.53 to 0.56 diopter [D]), were lower with the Baylor nomogram (0.21 to 0.26 D), and were lowest for the Barrett toric calculator (0.01 to 0.16 D) ( P P Conclusion Prediction of astigmatic outcomes with toric IOLs can be improved with appropriate measuring devices and methods to establish the required toric IOL power. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

95 citations


Cites background or methods or result from "Correcting astigmatism with toric i..."

  • ...Intraocular lens tilt, IOL rotational misalignment,(6) and unexpected surgically induced astigmatism (SIA)(2,7) all contribute to prediction errors; however, correcting for these factors does not always explain the postoperative astigmatic outcome.(4,8) Accurate correction of astigmatism requires accurate measurements....

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  • ...Methods of Calculation The online toric calculator by Alcon and the Holladay toric calculator were evaluated without and with the Baylor toric IOL nomogram adjustment.(8) The online Barrett toric calculator was evaluated without adjustment....

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  • ...The Baylor nomogram for the adjustment of toric IOL power to account for posterior corneal astigmatism is based on regression analysis.(8) The predicted net corneal astigmatism assessment for the Baylor nomogram was calculated using the published regression equations by subtracting (0....

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  • ...The predicted residual astigmatism at the corneal planewas calculated by the sum of the assumed toric IOL cylinder power at the corneal plane and the measured corneal astigmatism taken by each device with or without adjustments for the Baylor nomogram.(8) The error in the predicted residual astigmatism was calculated by subtracting the predicted residual astigmatism at the corneal plane from the postoperative subjective refraction at the corneal plane....

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  • ...These results correlate well with findings by Koch et al.(8) for WTR astigmatism and partially for ATR astigmatism....

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Journal ArticleDOI
TL;DR: Adjustment of commercial toric IOL calculators by the Abulafia‐Koch formula significantly improved the prediction of postoperative astigmatic outcome.
Abstract: Purpose To evaluate and compare the accuracy of 2 toric intraocular lens (IOL) calculators with or without a new regression formula. Setting Ein-Tal Eye Center, Tel-Aviv, Israel, and the Lions Eye Institute, Nedlands, Western Australia, Australia. Design Retrospective case series. Methods A new regression formula (Abulafia-Koch) was developed to calculate the estimated total corneal astigmatism based on standard keratometry measurements. The error in the predicted residual astigmatism was calculated by the Alcon and Holladay toric IOL calculators with and without adjustments by the Abulafia-Koch formula. These results were compared with those of the Barrett toric calculator. Results Data from 78 eyes were evaluated to validate the Abulafia-Koch formula. The centroid errors in predicted residual astigmatism were against-the-rule with the Alcon (0.55 diopter [D]) and Holladay (0.54 D) toric calculators and decreased to 0.05 D ( P x -axis], P = .776 [ y -axis]) and 0.04 D ( P x -axis], P = .726 [ y -axis]) with adjustments by the Abulafia-Koch formula. The Alcon and the Holladay toric calculators had a higher proportion of eyes within ±0.50 D of the predicted residual astigmatism with the Abulafia-Koch formula (76.9% and 78.2%, respectively) than without it (both 30.8%). There were no significant differences between the results of the Abulafia-Koch-modified Alcon and the Holladay toric calculators and those of the Barrett toric calculator. Conclusion Adjustment of commercial toric IOL calculators by the Abulafia-Koch formula significantly improved the prediction of postoperative astigmatic outcome. Financial Disclosure Dr. Abulafia received a speaker's fee from Haag-Streit AG. Dr. Barrett has licensed the Barrett Toric Calculator to Haag-Streit AG. Dr. Koch is a consultant to Alcon Laboratories, Inc., Abbott Medical Optics, Inc., and Revision Optics, Inc. Dr. Hill is a paid consultant to Haag-Streit AG and Alcon Laboratories, Inc. None of the other authors has a financial or proprietary interest in any material or method mentioned.

91 citations

References
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Journal ArticleDOI
TL;DR: Selecting toric intraocular lenses based on anterior corneal measurements could lead to overcor correction in eyes that have with‐the‐rule astigmatism and undercorrection in eyes which have against‐the-ruleAstigmatism.
Abstract: Purpose To determine the contribution of posterior corneal astigmatism to total corneal astigmatism and the error in estimating total corneal astigmatism from anterior corneal measurements only using a dual-Scheimpflug analyzer. Setting Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Design Case series. Methods Total corneal astigmatism was calculated using ray tracing, corneal astigmatism from simulated keratometry, anterior corneal astigmatism, and posterior corneal astigmatism, and the changes with age were analyzed. Vector analysis was used to assess the error produced by estimating total corneal astigmatism from anterior corneal measurements only. Results The study analyzed 715 corneas of 435 consecutive patients. The mean magnitude of posterior corneal astigmatism was −0.30 diopter (D). The steep corneal meridian was aligned vertically (60 to 120 degrees) in 51.9% of eyes for the anterior surface and in 86.6% for the posterior surface. With increasing age, the steep anterior corneal meridian tended to change from vertical to horizontal, while the steep posterior corneal meridian did not change. The magnitudes of anterior and posterior corneal astigmatism were correlated when the steeper anterior meridian was aligned vertically but not when it was aligned horizontally. Anterior corneal measurements underestimated total corneal astigmatism by 0.22 @ 180 and exceeded 0.50 D in 5% of eyes. Conclusions Ignoring posterior corneal astigmatism may yield incorrect estimation of total corneal astigmatism. Selecting toric intraocular lenses based on anterior corneal measurements could lead to overcorrection in eyes that have with-the-rule astigmatism and undercorrection in eyes that have against-the-rule astigmatism. Financial Disclosure The authors received research support from Ziemer Group. In addition, Dr. Koch has a financial interest with Alcon Laboratories, Inc., Abbott Medical Optics, Inc., Calhoun Vision, Inc., NuLens, and Optimedica Corp.

431 citations

Journal ArticleDOI
TL;DR: The shape of the anterior corneal surface provides no definitive basis for knowing the asphericity of the posterior surface and the results show the effective refractive index is 1.329, which is lower than values commonly used.

365 citations

Journal ArticleDOI
TL;DR: Analytical methods for evaluating the results of keratorefractive surgical procedures and emphasize the importance of intraocular astigmatism and the limitations of manual keratometry are demonstrated.
Abstract: Purpose To demonstrate analytical methods for evaluating the results of keratorefractive surgical procedures and emphasize the importance of intraocular astigmatism. Setting University of Texas Medical School, Houston, Texas, USA. Methods A standard data set, provided by an editor of this journal, comprising the preoperative and postoperative keratometric and refractive measurements of 100 eyes that had keratorefractive surgery was evaluated by 2 methods, vector and spheroequivalent (SEQ) analysis. The individual and aggregate surgically induced refractive changes (SIRCs) and prediction errors were determined from the refractive and keratometric measurements using both methods and then compared. The refraction vertex distance, keratometric index of refraction, and corneal asphericity were used to make the results calculated from refractive data directly comparable to those derived from keratometric data. Doubled-angle and equivalency plots as well as frequency and cumulative histograms were used to display the data. Standard descriptive statistics were used to determine the mean and standard deviation of the aggregate induced astigmatism after converting the polar values (cylinder and axis) to Cartesian (x and y) values. Results The preoperative SEQ refractive errors were undercorrected by at least 0.25 diopter (D) in most cases (78%). Six percent were corrected within ± 0.24 D, and 16% were overcorrected by at least 0.25 D SEQ. The mean SEQ was −6.68 D ± 2.49 (SD) before and −0.61 ± 0.82 D after surgery, reflecting a SIRC SEQ of −6.07 ± 2.40 D. The defocus equivalent (DEQ) was 7.41 ± 2.53 D before and 0.96 ± 0.74 D after surgery; for a nominal 3.0 mm pupil, this corresponded to an estimated improvement in uncorrected visual acuity (UCVA) from worse than 20/200 to better than 20/25, respectively. The predictability of the treatment decreased as the attempted refractive correction increased. The average magnitude of the refractive astigmatism was 1.46 ± 0.61 D before and 0.40 ± 0.38 D after surgery. The centroid of the refractive astigmatism was +0.96 × 87.9 ± 0.85 D, ρ = 0.43 before and +0.11 × 83.1 ± 0.37, ρ = 0.49 after surgery. The decrease in the square root of the centroid standard deviation shape factor (ρ1/2) indicated an 8% increase in the amount of oblique astigmatism in the population. The prevalence of preoperative keratometric irregular astigmatism in excess of 0.5 D in this group of patients was 13%. The correlation between keratometric and refractive astigmatism was extremely poor before (r2 = 0.26) and especially after surgery (r2 = 0.02), demonstrating the presence of intraocular astigmatism and the limitations of manual keratometry. The centroid of intraocular astigmatism at the corneal plane was +0.48 × 178 ± 0.49 D, ρ = 0.59, and was compensatory. Conclusions The 2 analytical methods are complimentary and permit thorough and quantitative evaluation of SIRCs and allow valid statistical comparisons within and between data sets. The DEQ allows comparison of refractive and visual results. The decrease in refractive predictability with higher corrections is well demonstrated by the SEQ and doubled-angle plots of the SIRC. Doubled-angle plots were particularly useful in interpreting errors of cylinder treatment amount and errors in alignment. The correlation between refractive and keratometric astigmatism was poor for preoperative, postoperative, and SIRC data, indicating the presence of astigmatic elements beyond the corneal surface (ie, intraocular astigmatism). Sources of error in refractive outcome statistics include the use of multiple lens systems in the phoropter, errors in vertex calculations, difficulty in accurately defining the axis of astigmatism, and failure to consider measurement errors when working with keratometric data. The analysis of this particular data set demonstrates the significant clinical benefits of refractive surgery: an 8-fold increase in UCVA, an 11-fold decrease in SEQ refractive error, as well as a 9-fold and nearly a 2 1/2-fold decrease in the magnitude and distribution of astigmatism, respectively.

293 citations

Journal ArticleDOI
TL;DR: The results indicate that phacoemulsification and posterior chamber AcrySof toric IOL implantation is an effective option to correct preexisting astigmatism in cataract surgery.
Abstract: PURPOSE: To evaluate the results of AcrySof toric intraocular lens (IOL) (Alcon) implantation to correct preexisting astigmatism in patients having cataract surgery. SETTING: Ophthalmology Service, Donostia Hospital, San Sebastian, Spain. METHODS: This prospective observational study included 30 eyes of 15 consecutive patients with more than 1.00 diopter (D) of preexisting corneal astigmatism having cataract surgery. Bilateral implantation of the AcrySof toric IOL was performed after phacoemulsification. The uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), residual refractive sphere, residual keratometric and refractive cylinders, and toric IOL axis were measured. RESULTS: The UCVA was 20/40 or better in 93.3% of eyes and 20/25 or better in 66.6%. All eyes achieved 20/25 or better BCVA. The mean refractive cylinder decreased significantly after surgery from 2.34 D G 1.28 (SD) to 0.72 G 0.43 D (P<.01). Vector analysis of attempted versus achieved correction showed that 100% of eyes were within G1.00 D and 80% and 93.9% were within G0.50 D for J0 and J45, respectively. The mean toric IOL axis rotation was 3.63 G 3.11 degrees, with rotation less than 10 degrees in 96.7% of eyes. CONCLUSIONS: The results indicate that phacoemulsification and posterior chamber AcrySof toric IOL implantation is an effective option to correct preexisting astigmatism in cataract surgery. The AcrySof toric IOL showed good rotational stability.

246 citations


"Correcting astigmatism with toric i..." refers methods in this paper

  • ...Prospectively, patients who were willing to participate in this study and met the following inclusion criteria were enrolled from July 2011 to September 2012: (1) good quality scans with all 5 devices, (2) no previous ocular trauma or surgery, (3) no corneal or other ocular disease, (4) no contact lens wear within 2 weeks before the corneal measurements, and (5) Acrysof toric IOL (models SN6AT3 to SN6AT8, Alcon Laboratories, Inc....

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