Corneal refractive power estimation and intraocular lens calculation after hyperopic LASIK

Abstract

Purpose: To identify key independent variables in estimating corneal refractive power (KBC) after hyperopic LASIK.

Design: Retrospective study.

Participants: We included 24 eyes of 16 hyperopic patients who underwent LASIK with subsequent phacoemulsification and posterior chamber intraocular lens (IOL) implantation in the same eye.

Methods: Pre-LASIK and post-LASIK spherical equivalent (SE) refractions and topographies, axial length, implant type and power, and 3-month postphacoemulsification SE were recorded. Using the double-K Hoffer Q formula, corneal power was backcalculated for every eye (KBC), regression-based formulas derived, and corresponding IOL powers calculated and compared with published methods.

Main outcome measures: The Pearson correlation coefficient (PCC) and arithmetic and absolute corneal and IOL power errors.

Results: Adjusting either the average central corneal power (ACCP(3mm)) or SimK based on the laser-induced spherical equivalent change (DeltaSE) resulted in an estimated corneal power (ACCP(adj) and SimK(adj)) with highest correlation with KBC (PCC=0.940 and 0.956, respectively) and lowest absolute corneal estimation error (0.37+/-0.45 and 0.38+/-0.39 diopter [D], respectively). The ACCP(adj) closely mirrored published DeltaSE-based adjustments of central corneal power on different topographers, whereas DeltaSE-based SimK adjustments varied across platforms. Using ACCP(adj) or SimK(adj) in the double-K Hoffer Q, using ACCP(3mm) or SimK in single-K Hoffer Q and adjusting the resultant IOL power based on DeltaSE, or applying Masket's formula all yielded accurate and similar IOL powers. The Latkany method consistently underestimated IOL power. The Feiz-Mannis and clinical history methods yielded poor IOL correlations and large IOL errors.

Conclusion: After hyperopic LASIK, adjusting either corneal power or IOL power based on DeltaSE accurately estimates the appropriate IOL power.