Impact of Corneal Aberrations and Lens Decentrations on the Performance of a Multifocal IOL

Abstract

Purpose:: To evaluate the optical performance and depth of focus (DOF) of a zonal multifocal intraocular lens (MIOL) when modeled with typical corneal aberrations from eyes following cataract extractions with lens replacements.

Methods:: A ReZoom (Advanced Medical Optics) MIOL was measured using a high resolution Shack-Hartmann wavefront sensor (133.33µm lenslet pitch, 3.75mm focal length). Zernike coefficients to the 14^th order were calculated for pupil diameters of 4.6mm (2 near and 2 far zones within the lens), 3.8mm (2 far and 1 near zone), and 3.4mm (1 near and 1 far zone). Corneal wave aberrations to the 5^th order from 21 eyes of 21 patients (age 71± 6.28 years) were used to predict total eye performance with the MIOL. The Visual Strehl ratio based on the optical transfer function (VSOTF) was calculated for centered and ±200µm decentrations (3.8mm, and 3.4mm pupils only). Retinal image quality defined as the VSOTF for values >=0.04 (approximately 0.3 LogMAR (Cheng, et al. J Vision 2004)) was calculated for a through focus of ±4 diopters (D). The Student’s t-Test was used to define the retinal image quality for determining DOF.

Results:: The dominant higher order aberrations for the MIOL were spherical aberrations (SA) which had values of -0.314µm (4^th), -0.120µm (6^th), 0.332µm (8^th), 0.053µm (10^th), -0.06µm (12^th), and 0.075µm (14^th) for a 4.6mm pupil. A DOF increase of 11% was noted when the pupil size decreased from 4.6mm to 3.4mm for just the lens aberrations. After combining the corneal and lens aberrations the VSOTF within the DOF decreased significantly by an average of 0.044 ± 0.011 for all 3 pupil diameters. While the largest DOF (approximately 4D) and the best average retinal image quality (VSOTF = 0.056 ± 0.001) over the DOF was maintained for the 3.4mm pupil after combining corneal and lens aberrations, decentering the lens with respect to the cornea by ±200µm for this pupil size resulted in a decrease of the DOF by approximately 80%. These decentrations also produced an overall shift of DOF to hyperopia.

Conclusions:: The ReZoom lens is dominated by aberrations with high spatial frequencies that were represented with radially symmetric 14^th order Zernikes. The added SA from this lens helps to increase the DOF, but large amounts of corneal aberrations and decentration may strongly decrease the effect.

Keywords: presbyopia • intraocular lens • optical properties