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.

New regression formula for toric intraocular lens calculations

Toric intraocular lenses (IOLs) are the procedure of choice to correct corneal astigmatism of 1 D or more in cases undergoing cataract surgery. Comprehensive literature search was performed in MEDLINE using "toric intraocular lenses," "astigmatism," and "cataract surgery" as keywords. The outcomes after toric IOL implantation are influenced by numerous factors, right from the preoperative case selection and investigations to accurate intraoperative alignment and postoperative care. Enhanced accuracy of keratometry estimation may be achieved by taking multiple measurements and employing at least two separate devices based on different principles. The importance of posterior corneal curvature is increasingly being recognized in various studies, and newer investigative modalities that account for both the anterior and posterior corneal power are becoming the standard of care. An ideal IOL power calculation formula should take into account the surgically induced astigmatism, the posterior corneal curvature as well as the effective lens position. Conventional manual marking has given way to image-guided systems and intraoperative aberrometry, which provide a mark-less IOL alignment and also aid in planning the incisions, capsulorhexis size, and optimal IOL centration. Postoperative toric IOL misalignment is the major factor responsible for suboptimal visual outcomes after toric IOL implantation. Realignment of the toric IOL is needed in 0.65%-3.3% cases, with more than 10° of rotation from the target axis. Newer toric IOLs have enhanced rotational stability and provide precise visual outcomes with minimal higher order aberrations.

Optimizing outcomes with toric intraocular lenses

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 Optikgerate, 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 Optikgerate, 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.

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

Purpose To compare the accuracy of intraocular lens (IOL) power calculation based on standard keratometry (K) and the new Total Keratometry (TK). Methods A post-hoc analysis of study data based on 145 pseudophakic astigmatic eyes was conducted. The absolute prediction error (APE) of spherical equivalent (SE) and cylinder (CYL) was calculated based on K and TK (including posterior corneal surface) data recorded 6 weeks after IOL implantation. APE was calculated as the difference between the postoperative refraction and the refractive error predicted by three classic IOL calculation methods (Haigis/Haigis-T, Barrett Universal II, Barrett Toric Calculator) and two new formulas developed for TK (Barrett TK Universal II, Barrett TK Toric). For APE in SE, the Haigis-T (K versus TK) and Barrett Universal II (K) versus Barrett TK Universal II (TK) were compared. For APE in CYL, the Haigis-T (K versus TK) and Barrett Toric Calculator (K) versus Barrett TK Toric formula (TK) were compared. Results Mean APE in SE and CYL was lower based on TK values compared to K, with a mean APE difference (K - TK) of 0.011 ± 0.107 diopters (D) (SE Haigis-T; 95% confidence interval [CI]: -0.004 to infinity), 0.016 ± 0.113 D (SE: Barrett Universal II versus Barrett TK Universal II; 95% CI: 0.0005 to infinity), 0.103 ± 0.173 D (CYL: Haigis-T; 95% CI: 0.0791 to infinity), and 0.020 ± 0.148 D (CYL: Barrett Toric versus Barrett TK Toric; 95% CI: -0.0002 to infinity). APE in SE was within ±0.50 D in 86% (Barrett TK Universal II) versus 84% (Barrett Universal II) of eyes. APE in CYL was within ±0.50 D in 58% (Haigis from TK) versus 44% (Haigis from K) of eyes. Conclusions In comparison to standard K, a higher prediction accuracy can be expected by using TK values along with the two newly developed formulas. TK values are compatible with standard IOL power calculation formulas and existing optimized IOL constants. [J Refract Surg. 2019;35(6):362-368.].

Prediction Accuracy of Total Keratometry Compared to Standard Keratometry Using Different Intraocular Lens Power Formulas

PURPOSE To compare the prediction error in the calculation of toric intraocular lenses (IOLs) associated with methods that estimate the power of the posterior corneal surface (ie, Barrett toric calculator and Abulafia-Koch formula) with that of methods that consider real measures obtained using Scheimpflug imaging: a software that uses vectorial calculation (Panacea toric calculator: http://www.panaceaiolandtoriccalculator.com) and a ray tracing software (PhacoOptics, Aarhus Nord, Denmark). METHODS In 107 eyes of 107 patients undergoing cataract surgery with toric IOL implantation (Acrysof IQ Toric; Alcon Laboratories, Inc., Fort Worth, TX), predicted residual astigmatism by each calculation method was compared with manifest refractive astigmatism. Prediction error in residual astigmatism was calculated using vector analysis. RESULTS All calculation methods resulted in overcorrection of with-the-rule astigmatism and undercorrection of against-the-rule astigmatism. Both estimation methods resulted in lower mean and centroid astigmatic prediction errors, and a larger number of eyes within 0.50 diopters (D) of absolute prediction error than methods considering real measures (P < .001). Centroid prediction error (CPE) was 0.07 D at 172° for the Barrett toric calculator and 0.13 D at 174° for the Abulafia-Koch formula (combined with Holladay calculator). For methods using real posterior corneal surface measurements, CPE was 0.25 D at 173° for the Panacea calculator and 0.29 D at 171° for the ray tracing software. CONCLUSIONS The Barrett toric calculator and Abulafia-Koch formula yielded the lowest astigmatic prediction errors. Directly evaluating total corneal power for toric IOL calculation was not superior to estimating it. [J Refract Surg. 2017;33(12):794-800.].

Comparison of Methodologies Using Estimated or Measured Values of Total Corneal Astigmatism for Toric Intraocular Lens Power Calculation.

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.

Adi Michaeli

Papers

Prediction of refractive outcomes with toric intraocular lens implantation.