Clinical Evaluation of a New Approach for IOL Power Calculation in Keratoconus

Abstract

Purpose: To obtain an expression of the adjusted IOL power (P IOLadj ) in keratoconus eyes associated with minimal errors in IOL power calculation. Materials and methods: This retrospective study included a total of 25 eyes of 25 patients with ages ranging from 20 years to 76 years. The following IOLs were implanted: Acrysof IQ Toric, Acrysof SA60AT in 9 eyes, Sensar in 3 eyes, Tecnis 1 in 4 eyes, and Tecnis Toric in 2 eyes. The P IOLadj is based on Gauss equations, using adjusted keratometric index (n kadj ) specific to keratoconus eyes. From this n kadj, an adjusted keratometric corneal power is calculated (P kadj ). The P IOLadj calculation was performed after estimating the effective lens position (ELP) using a mathematical expression obtained by multiple regression analysis (named ELP adj ). Comparison between the P IOLadj and the real intraocular power implanted in each patient (P IOLreal ) was carried out. Results: No significant differences between P IOLreal and P IOLadj were found. However, differences could be clinically relevant up to of 2.54 D as P IOLreal increases. But, in the range of P IOLreal between 0 and 20 D, differences were lower than 1.5 D, being most of them below 1 D. Conclusion:A new formula of IOL power calculation (P IOLadj ) based on the use of an adjusted keratometric power (P kadj ) that considers a variable keratometric index due to the influence of the posterior corneal surface (n kadj ) and adjusted effective lens position (ELP adj ) is useful for estimating IOL power in low-to-moderate keratoconus, with more limitation in the most advanced keratoconus.