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 (Delta) in SE (SEpostLASIK - SEpreLASIK) was simplified to AC-CPadj = ACCP(3mm) - 0.16 Delta SE, 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 ACCP3mm alone yielded 0.980 and 0.49 +/- 0.40 D, respectively. Using SimK with Delta SE 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 Delta SE was very accurate in predicting refractive corneal power after myopic LASIK followed by formulas based on ACCP(3mm) alone and SimK and Delta SE, all of which consolidate the validity of similar previously suggested methods, including EffRP(adjusted).