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.
Received 23 January 2004; accepted 12 April 2004. published online 16 September 2004.
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.
1Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA
Correspondence to Douglas D. Koch, MD, Cullen Eye Institute, Baylor College of Medicine, 6565 Fannin, NC205, Houston, TX 77030, USA.
ABSTRACT