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

Purpose: To obtain an expression of the adjusted IOL power (PIOLadj) 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 PIOLadj is based on Gauss equations, using adjusted keratometric index (nkadj) specific to keratoconus eyes. From this nkadj, an adjusted keratometric corneal power is calculated (Pkadj). The PIOLadj calculation was performed after estimating the effective lens position (ELP) using a mathematical expression obtained by multiple regression analysis (named ELPadj). Comparison between the PIOLadj and the real intraocular power implanted in each patient (PIOLreal) was carried out. Results: No significant differences between PIOLreal and PIOLadj were found. However, differences could be clinically relevant up to of 2.54 D as PIOLreal increases. But, in the range of PIOLreal 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 (PIOLadj) based on the use of an adjusted keratometric power (Pkadj) that considers a variable keratometric index due to the influence of the posterior corneal surface (nkadj) and adjusted effective lens position (ELPadj) is useful for estimating IOL power in low-to-moderate keratoconus, with more limitation in the most advanced keratoconus.