Elsevier

Ophthalmology

Volume 111, Issue 10, October 2004, Pages 1825-1831
Ophthalmology

Original article
Comparison of intraocular lens power calculation methods in eyes that have undergone LASIK

Presented at: American Society of Cataract and Refractive Surgery Symposium on Cataract, Intraocular Lens, and Refractive Surgery, April, 2003; San Francisco, California.
https://doi.org/10.1016/j.ophtha.2004.04.022Get rights and content

Abstract

Objective

To compare methods of calculating intraocular lens (IOL) power for cataract surgery in eyes that have undergone myopic LASIK.

Design

Noncomparative case series.

Participants

Eleven eyes of 8 patients who had previously undergone myopic LASIK (amount of LASIK correction [±standard deviation], −5.50±2.61 diopters [D]; range, −8.78 to −2.38 D) and subsequently phacoemulsification with implantation of the SA60AT IOLs (Alcon Surgical, Inc., Fort Worth, TX) were included (refractive error after cataract surgery, −0.61 ± 0.79 D; range, −2.0 to 1.0 D).

Methods

We evaluated the accuracy of various combinations of: (1) single-K versus double-K (in which pre-LASIK keratometry is used to estimate effective lens position) versions of the IOL formulas; the Feiz–Mannis method was also evaluated; (2) 4 methods for calculating corneal refractive power (clinical history, contact lens overrefraction, adjusted effective refractive power [EffRPadj], and Maloney methods); and (3) 4 IOL formulas (SRK/T, Hoffer Q, Holladay 1, and Holladay 2). The IOL prediction error was obtained by subtracting the IOL power calculated using various methods from the power of the implanted IOL, and the F test for variances was performed to assess the consistency of the prediction performance by different methods.

Main outcome measures

Mean arithmetic IOL prediction error, mean absolute IOL prediction error, and variance of the IOL prediction error.

Results

Compared with double-K formulas, single-K formulas predicted lower IOL powers than the power implanted and would have left patients hyperopic in most cases; the Feiz–Mannis method had the largest variance. For the Hoffer Q and Holladay 1 formulas, the variances for EffRPadj were significantly smaller than those for the clinical history method (0.43 D2 vs. 1.74 D2, P = 0.018 for Hoffer Q; 0.75 D2 vs. 2.35 D2, P = 0.043 for Holladay 1). The Maloney method consistently underestimated the IOL power but had significantly smaller variances (0.19–0.55 D2) than those for the clinical history method (1.09–2.35 D2; P<0.015). There were no significant differences among the variances for the 4 formulas when using each corneal power calculation method.

Conclusions

The most accurate method was the combination of a double-K formula and corneal values derived from EffRPadj. The variances in IOL prediction error were smaller with the Maloney and EffRPadj methods, and we propose a modified Maloney method and second method using Humphrey data for further evaluation.

Section snippets

Patients

On obtaining institutional review board approval, we analyzed IOL power results in 11 consecutive eyes of 8 patients who had previously undergone LASIK for myopia and underwent cataract surgery at some point from July 2002 through July 2003. All cataract surgeries were performed in the same manner by the same surgeon (DDK) using a temporal clear corneal incision, phacoemulsification, and implantation of the SA60AT IOL (Alcon Surgical, Inc., Fort Worth, TX). Before surgery, the clinical history

Results

The mean age of the 8 patients was 50 years (range, 37–60 years). The amount of LASIK-induced correction (±standard deviation) was −5.50±2.61 D (range, −8.78 to −2.38 D), and the mean manifest refraction after cataract surgery was −0.61±0.79 D (range, −2.0 to 1.0 D; Table 1). The eye with the greatest amount of hyperopia was 1 of the 2 eyes for which we used the single-K Holladay 1 formula (case 7). To illustrate the spectrum of outcomes for each eye, the IOL prediction errors with Holladay 2

Discussion

The reduced accuracy of IOL calculations after corneal refractive surgery is a clinical problem of growing importance. Although published studies suggest that the clinical history method is a helpful approach for calculating corneal power, the numbers of eyes in these studies were small, and unacceptably large refractive surprises still occurred.3, 17, 18 Using the Holladay 2 formula, Randleman et al17 evaluated the accuracy of several techniques for calculating IOL power in 10 LASIK eyes. They

References (24)

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Manuscript no. 240063.

Supported by an unrestricted grant from Research to Prevent Blindness, Inc., New York, New York.

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