Customizing Selection of IOL Asphericity Based on Pre-Existing Corneal HOAs

Abstract

Purpose:: Using computer modeling, to investigate the amount of ocular spherical aberration (SA, Z₄⁰) needed to optimize optical quality in eyes with normal pre-existing corneal higher-order aberrations (HOAs).

Methods:: For 154 eyes in patients with ages 40 to 80 years, we simulated implantation of IOLs with varying amounts of SA to achieve ocular SA of -0.3 µm to +0.3 µm (in 0.05-µm intervals). In this model, there was full correction of lower-order aberrations; pre-existing corneal HOAs from 3^rd-6^th order other than SA were not corrected. Using the ZernikeTool program (AMO, Inc), we calculated the polychromatic modulation transfer function volumes (MTFVs) with Stiles-Crawford effect up to 30 cyc/deg. For each eye, the amount of SA needed to obtain the greatest MTFV was determined. Stepwise multiple regression analysis was used to determine the Zernike terms that best predicted the amount of SA required to maximize the MTFV.

Results:: Among the 154 eyes, the percentages of eyes with the greatest MTFV were 44.8% at SA of -0.05 µm, 24.7% at SA of zero, 12.3% at SA of -0.1 µm, 4.5% at SA of +0.05 µm, 3.9% at SA of -0.15 µm, 3.2% at -0.20 µm, 2.6% at SA of -0.25 µm and -0.30 µm, 0.6% at SA of +0.1 µm. Thus 69.5% had best optical quality when ocular SA was negative. Zernike terms Z₃¹, Z₄^-4, Z₄², Z₆⁰ and Z₆² were significant predictors to the SA (adjusted R Square=0.404); Z₆⁰ made the greatest contribution, followed by Z₆², Z₄², Z₃¹ and Z₄^-4.

Conclusions:: In the majority of eyes with a normally distributed corneal higher-order aberrations, optical quality was optimized with a small amount of negative ocular SA. Customization of IOL selection should perhaps be based on the full spectrum of pre-existing corneal HOAs and not on 4^th order SA alone.

Keywords: intraocular lens • cataract • contrast sensitivity