Intraocular lens power calculation after myopic laser in situ keratomileusis: Estimating the corneal refractive power

Purpose: To derive regression-based formulas and identify essential dependent variables to estimate refractive corneal power after myopic laser in situ keratomileusis (LASIK). Setting: University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, USA. Methods: A retrospective data review of 30 eyes (23 patients) having myopic LASIK followed by phacoemulsification and posterior chamber intraocular lens (IOL) implantation in the same eye gathered the following: pre-LASIK and post-LASIK refractions and topographies, axial length, IOL type and power, and spherical equivalent (SE) refraction 3 months after phacoemulsification. Using the double-K Holladay 1 formula, the refractive corneal power in each eye was back-calculated. Regression formulas were derived and compared with current corneal power estimation methods. Results: The multiple regression formula based on the average corneal power in the central 3.0 mm area (ACCP_3mm) and the change (Δ) in SE (SE_postLASIK - SE_preLASIK) was simplified to ACCP_adj = ACCP_3mm - 0.16ΔSE, with the highest Pearson correlation coefficient (r = 0.989) and lowest absolute corneal power estimation error (0.30 diopter [D] ± 0.30 (SD)). Regression based on ACCP_3mm alone yielded 0.980 and 0.49 ± 0.40 D, respectively. Using SimK with ΔSE resulted in a lower r value (0.971) and larger absolute corneal power estimation error (0.65 ± 0.44 D) (P = .0014). The clinical history methods yielded 0.909 and 1.09 ± 0.868 D, respectively (P = .0005). Conclusion: The regression formula based on ACCP_3mm and ΔSE was very accurate in predicting refractive corneal power after myopic LASIK followed by formulas based on ACCP_3mm alone and SimK and ΔSE, all of which consolidate the validity of similar previously suggested methods, including EffRP_adjusted.