Cataract in the Adult Eye Preferred Practice Pattern

Purpose To assess the accuracy of 7 intraocular lens (IOL) power formulas (Barrett Universal II, Haigis, Hoffer Q, Holladay 1, Holladay 2, SRK/T, and T2) using IOLMaster biometry and optimized lens constants. Setting Public hospital ophthalmology department. Design Retrospective case series. Methods Data from patients having uneventful cataract surgery with Acrysof IQ SN60WF IOL implantation over 5 years were obtained from the biometry and patient charts. Optimized lens constants were calculated for each formula and used to determine the predicted refractive outcome for each patient. This was compared with the actual refractive outcome to give the prediction error. Eyes were separated into subgroups based on axial length (AL) as follows: short (≤22.0 mm), medium (>22.0 to Results The study included 3241 patients. The Barrett Universal II formula had the lowest mean absolute prediction error over the entire AL range ( P P P P Conclusion In eyes with an AL longer than 22.0 mm, the Barrett Universal II formula was a more accurate predictor of actual postoperative refraction than the other formulas. Financial Disclosure None of the authors has a financial or proprietary interest in any material or method mentioned.

Intraocular lens power formula accuracy: Comparison of 7 formulas.

Protocols for studies of intraocular lens formula accuracy.

1. Range of analytical approaches. In the January 2001 issue of JCRS, several authors described their methods for analyzing change in corneal astigmatism following laser in situ keratomileusis surgery. Several of these methods are commonly and effectively used in peerreviewed scientific studies to characterize astigmatic changes. 2. Analyzing astigmatic change in intraocular lens (IOL)-based surgery is more complex than in corneal refractive surgery. One issue is simply the transition of terminology and standards for reporting outcomes from corneal laser refractive surgery to toric-IOL-based surgery, which was recently addressed by a joint editorial in the Journal of Cataract & Refractive Surgery and the Journal of Refractive Surgery. A larger problem is complexity of measurement and analysis. With corneal refractive surgery, we evaluate changes in two measurable entities: refraction and anterior corneal curvature. With IOL-based surgery, however, parameters required to analyze astigmatic change after cataract surgery include: (a) refraction; (b) anterior corneal astigmatism; (c) posterior corneal astigmatism, which still eludes consistently accurate measurement; (d) IOL alignment, which must be rigorously measured; (e) effective IOL toricity at corneal plane, which can be calculated but not directly measured; and (f) IOL tilt, which induces astigmatism with nontoric and toric IOLs. 3. There are four clinical scenarios in which cataract surgery alters ocular astigmatism. They are: (a) nontoric IOL without corneal relaxing incisions, (b) nontoric IOL with corneal relaxing incisions, (c) toric IOL without corneal relaxing incisions, and (d) toric IOL with corneal relaxing incisions. Since both the cornea and IOL have an astigmatic component (tilt in the case of a spherical IOL), for each of these scenarios we are interested in the corneal, IOL-induced, and total ocular astigmatism (which is typically characterized by the manifest refractive astigmatism, but objective measures of ocular astigmatism can also be used).

Pursuing perfection in intraocular lens calculations: IV. Rethinking astigmatism analysis for intraocular lens-based surgery: Suggested terminology, analysis, and standards for outcome reports.

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

Purpose To evaluate and compare the accuracy of formulas and methods for calculating the intraocular lens (IOL) power for eyes with an axial length (AL) greater than 26.0 mm. Setting Ein-Tal Eye Center, Tel-Aviv, Israel. Design Retrospective case series. Methods The postoperative refraction results in myopic eyes with an AL over 26.0 mm were compared with the predicted refractions calculated using standard formulas (Holladay 1, SRK/T, Hoffer Q, and Haigis) with optical IOL constants, User Group for Laser Interference Biometry constants, and an AL-adjustment method and using new-generation formulas (Barrett Universal II, Holladay 2, and Olsen). Results In 76 (71.7%) of 106 eyes, the IOL was 6.0 diopters (D) or more (Group A) and in 30 eyes (28.3%) was less than 6.0 D (Group B). In Group A, the SRK/T, Hoffer Q, Haigis, Barrett Universal II, Holladay 2, and Olsen methods met the benchmark criteria of having a prediction error of ±0.5 D in at least 71.0% of eyes and ±1.0 D in 93.0% of eyes. In Group B, only the Barrett Universal II formula and the Holladay 1 and Haigis formulas using the AL-adjusted method met those criteria. Conclusion When selecting IOLs for high and extreme myopia, choosing appropriate formulas and methods can yield accurate refractive results that meet benchmark criteria. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Intraocular lens power calculation for eyes with an axial length greater than 26.0 mm: Comparison of formulas and methods

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.

Ehud I. Assia

Papers

Intraocular lens power calculation for eyes with an axial length greater than 26.0 mm: Comparison of formulas and methods

Prediction of refractive outcomes with toric intraocular lens implantation.

New regression formula for toric intraocular lens calculations