Comparison of intraocular lens power calculation methods in eyes that have undergone laser-assisted in-situ keratomileusis.

PURPOSE

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

METHODS

Eleven eyes of eight patients who had previously undergone myopic LASIK (amount of LASIK correction, -5.50 +/- 2.61 D (SD); range, -8.78 to -2.38 D) and subsequently phacoemulsification with implantation of the SA60AT IOLs were included (refractive error after cataract surgery, -0.61 +/- 0.79 D; range, -2.0 to 1.0 D). 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) four methods for calculating corneal refractive power (clinical history, contact lens overrefraction, adjusted EffRP (EffRP(adj)), and Maloney methods); and (3) four 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.

RESULTS

Compared to double-K formulas, single-K formulas predicted lower IOL powers than the power implanted and would have left patients hyperopic in the majority of the cases; the Feiz-Mannis method had the largest variance. For the Hoffer Q and Holladay 1 formulas, the variances for EffRP(adj) were significantly smaller than those for the clinical history method (0.43 D2 vs 1.74 D2, P = .018 for Hoffer Q; 0.75 D2 vs 2.35 D2, P = .043 for Holladay 1). The Maloney method consistently underestimated the IOL power but had significantly smaller variances (0.19 to 0.55 D2) than those for the clinical history method (1.09 to 2.35 D2) (P < .015). There were no significant differences among the variances for the four 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 EffRP(adj). The variances in IOL prediction error were smaller with the Maloney and EffRP(adj) methods, and we propose a modified Maloney method and second method using Humphrey data for further evaluation.