Intraocular lens power calculation in post-myopic-LASIK eyes: comparison of two different corneal refractive power measurements by Pentacam

Objectives To compare the accuracy of two different corneal refractive power measurements in intraocular lens (IOL) power calculation in post-myopic-LASIK eyes.Methods Post-myopic-LASIK patients scheduled for cataract surgery were enrolled. Corneal refractive power centered on corneal apex (K_apex) and pupil center (K_pupil), decentration of ablation zone, and Kappa angle were measured by Pentacam. Predicted postoperative spherical equivalence (SE) was calculated using K_apex and K_pupil, respectively. Prediction error was calculated as actual SE minus predicted SE. Mean error (ME), mean absolute error (MAE), and median absolute error (MedAE) were compared between K_apex and K_pupil groups, with subgroup analysis in terms of decentered ablation and Kappa angle.Results Totally 92 eyes were analyzed. ME, MAE and MedAE with K_apex were all lower than those with K_pupil (-0.42 ± 1.06 vs -0.64 ± 1.21 D, 0.89 ± 0.71 vs 1.01 ± 0.92 D, 0.69 vs 0.76 D, respectively; P < 0.05 for ME and MedAE). In both subgroups of larger decentration of ablation zone and larger Kappa angle, ME with K_apex was lower than that with K_pupil to a higher degree (both P < 0.05). Average K_apex was higher than average K_pupil (P < 0.001). Multivariate analysis demonstrated that prediction error with K_pupil was associated with decentration of ablation zone (β=-0.264, P = 0.019), while no such association was found in prediction error with K_apex.Conclusions The K_apex achieved better accuracy in IOL power calculation than K_pupil in post-myopic-LASIK eyes, especially in eyes with large decentration of ablation zone or large Kappa angle.