Efficacy of segmented axial length and artificial intelligence approaches to intraocular lens power calculation in short eyes.

PURPOSE: In short eyes, to compare the predictive accuracy of newer intraocular lens (IOL) power calculation formulas using traditional and segmented axial length (AL) measurements. SETTING: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas and East Valley Ophthalmology, Mesa, Arizona. DESIGN: Multi-center retrospective case series. METHODS: Measurements from an optical biometer were collected in eyes with AL <22 mm. IOL power calculations were performed with 15 formulas using 2 AL values: (1) machine-reported traditional AL (Td-AL) and (2) segmented AL calculated with the Cooke-modified AL nomogram (CMAL). 1 AL method and 7 formulas were selected for pairwise analysis of mean absolute error (MAE) and root mean square absolute error (RMSAE). RESULTS: The study comprised 278 eyes. Compared with the Td-AL, the CMAL produced hyperopic shifts without differences in RMSAE. The ZEISS AI IOL Calculator (ZEISS AI), K6, Kane, Hill-RBF, Pearl-DGS, EVO, and Barrett Universal II (Barrett) formulas with Td-AL were compared pairwise. The ZEISS AI demonstrated smaller MAE and RMSAE than the Barrett, Pearl-DGS, and Kane. K6 had a smaller RMSAE than the Barrett formula. In 73 eyes with shallow anterior chamber depth, the ZEISS AI and Kane had a smaller RMSAE than the Barrett. CONCLUSIONS: ZEISS AI outperformed Barrett, Pearl-DGS, and Kane. The K6 formula outperformed some formulas in selected parameters. Across all formulas, use of a segmented AL did not improve refractive predictions.

Accuracy of intraocular lens power calculation methods when targeting low myopia in monovision.

PURPOSE: To investigate the accuracy of IOL power calculation methods for refractive targets of myopia compared with emmetropia. SETTING: Lions Eye Institute, Perth, Australia. DESIGN: Retrospective analysis. METHODS: Patients undergoing bilateral, sequential cataract surgery with a plan of modest monovision were analyzed. Target refraction was plano (distance eye) and -1.25 diopters (D) (near eye). Prediction error was determined by comparing the actual postoperative refraction with the predicted postoperative refraction, calculated by the Barrett Universal II (BUII), Hill-RBF version 2.0 (Hill-RBF 2.0), Haigis, Holladay 1, SRK/T, and Hoffer Q formulas. The dataset was divided into distance and near eye subgroups. Mean and median absolute error and percentage of eyes within ±0.25, ±0.50, ±0.75, and ±1.00 D of refractive target were compared. RESULTS: The study included 88 consecutive patients. There was a consistent trend for lower refractive accuracy in the near eyes. BUII and Hill-RBF 2.0 were the most accurate overall and least affected by this phenomenon, with 1 (1.1%) and 4 (4.6%) fewer eyes, respectively, in the near subgroup achieving ±0.50 D of target. Haigis and SRK/T were most affected, with 14 (15.9%) and 11 (12.5%) fewer near eyes achieving ±0.50 D of target (P < .05). Holladay 1 and Hoffer Q occupied the middle ground, with 6 (6.8%) and 9 (10.2%) fewer near eyes achieving ±0.50 D of target. CONCLUSIONS: IOL-power calculation formulas appear to be less accurate when targeting myopia compared with emmetropia. BUII and Hill-RBF 2.0 represented good options when planning pseudophakic monovision as they were least affected by this phenomenon and can be used for both distance and near eyes.

Intraocular Lens Power Calculation in Eyes After Laser In Situ Keratomileusis or Photorefractive Keratectomy for Myopia.

Intraocular power calculation is challenging for patients who have previously undergone corneal refractive surgery. The sources of prediction errors for these eyes are well known; however, the numerous formulas and methods available for calculating intraocular lens power in these cases are eloquent testimony to the absence of a definitive solution. This review discusses some of the available methods for improving the accuracy for predicting the refractive outcome for these patients. It focuses mainly on the methods available on the American Society of Cataract and Refractive Surgery (ASCRS) online calculator and provides some practical guidelines for cataract surgeons who encounter these challenging cases.

New regression formula for toric intraocular lens calculations.

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 < .001 [x-axis], P = .776 [y-axis]) and 0.04 D (P < .001 [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.

Accuracy of the Barrett True-K formula for intraocular lens power prediction after laser in situ keratomileusis or photorefractive keratectomy for myopia.

PURPOSE: To compare the accuracy of the Barrett True-K formula with other methods available on the American Society of Cataract and Refractive Surgery (ASCRS) post-refractive surgery intraocular lens (IOL) power calculator for the prediction of IOL power after previous myopic laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK). SETTING: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, and private practice, Mesa, Arizona, USA. DESIGN: Retrospective case series. METHODS: The accuracy of the Barrett True-K formula was compared with the Adjusted Atlas (4.0 mm zone), Masket, modified-Masket, Wang-Koch-Maloney, Shammas, and Haigis-L methods to calculate IOL power. A separate analysis of 2 no-history methods (Shammas and Haigis-L) was performed and compared with the Barrett True-K no-history option. RESULTS: Eighty-eight eyes were available for analysis. The Barrett True-K formula had a significantly smaller median absolute refraction prediction error than all other formulas except the Masket, smaller variances compared with the Wang-Koch-Maloney, Shammas, and Haigis-L, and a greater percentage of eyes within ±0.50 diopter (D) of predicted error in refraction compared with the Adjusted Atlas, Masket, and modified Masket methods (all P < .05). In eyes with no historical data, the Barrett True-K no-history formula had a significantly smaller median absolute refraction prediction error and a greater percentage of eyes within ±0.50 D of the predicted error in refraction than the Shammas and the Haigis-L formulas (both P < .05). CONCLUSION: The Barrett True-K formula was either equal to or better than alternative methods available on the ASCRS online calculator for predicting IOL power in eyes with previous myopic LASIK or PRK.

Comparison of Methods to Predict Residual Astigmatism After Intraocular Lens Implantation.

PURPOSE: To evaluate and compare the accuracy of three toric intraocular lens (IOL) calculators using keratometry measurements derived from the anterior corneal curvature and direct measurements of the posterior corneal curvature. METHODS: Postoperative corneal astigmatism was measured by the IOLMaster (Carl Zeiss Meditec, Jena, Germany) and Pentacam (Oculus Optikgeräte, Wetzlar, Germany). The data were processed by the Alcon, Holladay, and Barrett toric IOL calculators. The error in predicted residual astigmatism (PredRA) was calculated by subtracting the PredRA from the postoperative subjective refraction by vector analysis. RESULTS: The centroid errors in PredRA were against-the-rule (ATR) with the Alcon (0.56 diopters [D]) and Holladay (0.55 D) toric calculators using the IOLMaster (Carl Zeiss Meditec, Jena, Germany) measurements. The centroid errors in PredRA were lower when Pentacam (Oculus Optikgeräte, Wetzlar, Germany) measurements were used (0.38 D, ATR). The Barrett toric calculator using the IOLMaster measurements had the lowest centroid errors in PredRA (0.02 D, P < .001) and achieved the most accurate results: 75.8% and 92.9% of eyes were within 0.50 and 0.75 D of the PredRA, respectively. CONCLUSIONS: The prediction of the postoperative astigmatic outcome can be improved by using appropriate methods of adjustment for posterior corneal astigmatism.

Optical bench performance of AcrySof(®) IQ ReSTOR(®), AT LISA(®) tri, and FineVision(®) intraocular lenses.

PURPOSE: To compare the resolution and optical quality of the ReSTOR(®) +3.0 D and ReSTOR +2.5 D multifocal intraocular lenses (IOLs) with the AT LISA(®) tri and FineVision(®) trifocal IOLs. METHODS: Resolution, image quality, and photic phenomena were evaluated in the AcrySof(®) IQ ReSTOR +3.0 D and +2.5 D multifocal IOLs and compared with the AT LISA tri 839MP and FineVision Micro F12 trifocal IOLs, using a Badal optometer and a Snellen visual acuity chart. Simulated headlight images were obtained using a modulation transfer function (MTF) bench and a 50 µm pinhole target. MTF values, using vertical and horizontal slits, were determined at far, intermediate, and near distances. RESULTS: Resolution at 20/40 Snellen visual acuity equivalence was attainable over nearly the entire viewing distance range with the AT LISA tri and FineVision IOLs, but background shadows were more prominent with the AT LISA tri and FineVision IOLs than with the ReSTOR IOLs. Distance MTF peaks at 20/20 Snellen-equivalent spatial frequency were greatest for ReSTOR +2.5 D and ReSTOR +3.0 D IOLs. The near MTF peak occurred at 53 cm with ReSTOR +2.5 D and had a 20/20 Snellen-equivalent value that was lower than the near peaks of the other models but higher than the intermediate foci of the trifocal IOLs. CONCLUSION: AT LISA tri and FineVision trifocal IOLs achieved a useful third focus for intermediate vision but were associated with increased background halos and reduced distance visual quality compared with ReSTOR +2.5 D and +3.0 D multifocal IOLs.

Intraocular lens power calculation in eyes with previous hyperopic laser in situ keratomileusis.

PURPOSE: To establish a corneal correction equation for the Shammas post-hyperopic laser in situ keratomileusis (LASIK) (Shammas-PHL) formula and to evaluate its accuracy in cases with and without available pre-LASIK data. SETTING: Private practices, Lynwood, California, and Mesa, Arizona, USA. DESIGN: Retrospective comparative observational study. METHODS: The corrected corneal power (Kc) was calculated in each eye by adding the refractive change at the corneal level to the pre-LASIK keratometric (K) readings. By comparing Kc with the measured post-LASIK K readings (Kpost), the following equation was derived: Kc = 1.0457 Kpost-1.9538. This equation was combined with the Shammas original formula to obtain the Shammas-PHL formula. RESULTS: The new formula was evaluated in 18 eyes with previous LASIK data and in 24 eyes with no previous LASIK data. Using the Shammas-PHL formula, the mean arithmetic prediction error was -0.03 diopter (D) ± 0.72 (SD) (range -1.57 to +1.54 D) and the median absolute error was 0.38 D in 18 eyes with available pre-LASIK data and 0.05 ± 0.58 D (range -0.56 to +1.40 D) and 0.43 D, respectively, in the 24 eyes with no pre-LASIK data. CONCLUSION: The Shammas-PHL formula can be used in post-hyperopic LASIK cases whether or not the pre-LASIK data are available.

Prospective multicenter study of toric IOL outcomes when dual zone automated keratometry is used for astigmatism planning.

PURPOSE: To evaluate clinical outcomes when toric intraocular lens (IOL) calculations are based on the keratometric output from the Lenstar LS-900 dual zone automated keratometer (Haag-Streit AG, Koeniz, Switzerland). METHODS: Eligible subjects presenting for toric IOL implantation at five sites were measured with a dual-zone automated keratometer. The data were used to plan the power and angle of the toric IOL to be implanted. Refractive and visual acuity status were checked at 1 and 3 months postoperatively. RESULTS: A total of 102 eyes had relevant data for analysis. More than 76% of eyes had 0.50 diopter or less of refractive astigmatism at 1 and 3 months, with no difference by level of astigmatism corrected. More than half of the eyes had uncorrected distance visual acuity of 20/20 or better and 78% were 20/25 or better. A new measure of effectiveness of toric correction power is described that suggested lens selection was appropriate. Results appeared better than those obtained in previous studies when the IOL cylinder power and alignment were calculated using manual keratometry. CONCLUSIONS: In this series of eyes from multiple centers, the calculation of toric IOL power using dual-zone automated keratometry measurements produced clinical results that were better than results in the literature where manual keratometry was used.

Matched comparison of rotational stability of 1-piece acrylic and plate-haptic silicone toric intraocular lenses in Asian eyes.

PURPOSE: To evaluate and compare the postoperative rotational stability of a 1-piece acrylic toric intraocular lens (IOL) (Acrysof) and a plate-haptic silicone toric IOL (Staar) in Asian eyes. SETTING: Singapore National Eye Centre, Singapore. DESIGN: Prospective randomized control trial. METHODS: Eyes of Chinese patients having cataract surgery were randomized to receive the acrylic toric IOL or the silicone toric IOL. Postoperatively, patients returned at 1 day, 1 week, and 1 and 3 months. The eyes were dilated and slitlamp retroillumination photography of the toric IOL was performed to assess rotational stability. RESULTS: The acrylic IOL was implanted in 24 eyes and the silicone IOL in 26 eyes. The mean age of the patients was 68.2 years (range 42 to 82 years). The mean IOL rotation from baseline to 3 months postoperatively was 4.23 ± 4.28 degrees in the acrylic IOL group and 9.42 ± 7.80 degrees in the silicone IOL group; the difference was statistically significant (P=.01). Of the acrylic IOLs, 73% were rotated less than 5 degrees at 3 months; none was rotated more than 15 degrees at 3 months. The silicone toric IOLs showed greater rotational movement, with 37% being rotated less than 5 degrees and 21% being rotated more than 15 degrees. CONCLUSION: The acrylic toric IOL had better rotational stability than the silicone toric IOL.

Evaluation of intraocular lens power prediction methods using the American Society of Cataract and Refractive Surgeons Post-Keratorefractive Intraocular Lens Power Calculator.

PURPOSE: To evaluate the accuracy of methods of intraocular lens (IOL) power prediction after previous laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) using the American Society of Cataract and Refractive Surgery IOL power calculator. SETTING: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, and private practice, Mesa, Arizona, USA. METHODS: The following methods were evaluated: methods using pre-LASIK/PRK keratometry (K) and surgically induced change in refraction, methods using surgically induced change in refraction, and methods using no previous data. The predicted IOL power was calculated with each method using the actual refraction after cataract surgery as the target. The IOL prediction error was calculated as the implanted IOL power minus the predicted IOL power. Arithmetic and absolute IOL prediction errors, variances in mean arithmetic IOL prediction error, and percentage of eyes within +/-0.50 diopter (D) and +/-1.00 D of refractive prediction errors were calculated. RESULTS: Methods using surgically induced change in refraction or no previous data had significantly smaller mean absolute IOL prediction errors, smaller variances, and a greater percentage of eyes within +/-0.50 D and +/-1.00 D of refractive prediction errors than methods using pre-LASIK/PRK keratometry (K) values and surgically induced change in refraction (all P<.05 with Bonferroni correction). There were no statistically significant differences between methods using surgically induced change in refraction and methods using no previous data. CONCLUSION: Methods using surgically induced change in refraction and methods using no previous data gave better results than methods using pre-LASIK/PRK K values and surgically induced change in refraction.

Corneal power measurements using scheimpflug imaging in eyes with prior corneal refractive surgery.

PURPOSE: To evaluate the accuracy of central corneal power measurements by Scheimpflug imaging (Pentacam) for eyes that had corneal refractive surgery. METHODS: This study comprised two groups: a pilot group of 100 eyes with prior hyperopic or myopic LASIK that did not have cataract surgery, and a test group of 41 eyes with prior radial keratotomy (RK) and cataract surgery. In the pilot group, Pentacam images and refraction were taken preoperatively and 3 months after LASIK. The historical method was used to compute the theoretical postoperative keratometry (K) -reading and then compared to the measured equivalent K-reading (EKR) from the Pentacam. The EKR is the same value measured by standard keratometry or topography on the front surface, adjusted for the effect of the back surface power difference from normal. In the test group of RK eyes, the postoperative refraction and EKR were measured 3 months after cataract surgery. The Holladay IOL Consultant Program was used to back-calculate the theoretical K-reading. The EKR measurements were then compared to the back-calculated corneal power. RESULTS: The optimal zone sample size was determined to be 4.5 mm for the pilot group. The mean prediction error for this group was -0.06+/-0.56 diopters (D) (range: -1.63 to +/-1.34 D). Using the 4.5-mm zone determined in the pilot group, the EKR value for the test group of 41 RK eyes had a mean prediction error of -0.04+/-0.94 D (range: -1.84 to +/-2.27 D). CONCLUSIONS: When historical refractive data are not available, Scheimpflug imaging with the Pentacam provides an alternative method of measuring the central corneal power in eyes that previously received corneal refractive surgery.