The Optical Performance Parameters for Rotation and Decentration of the Aspherical Biconvex Toric Intraocular Lens

Abstract

Objective: To optimize the spherical aberrations of toric intraocular lens (IOL): to design toric IOLs with different spherical aberrations, and to study the rotation, the tolerance to decentration, and imaging rules. Methods: In this experimental study, the spherical aberrations of toric IOLs were optimized in the Hwey-Lan Liou model eye. The spherical structure, the curvature radius, and the thickness of the anterior and posterior surfaces of the toric IOLs, and the aspheric coefficients of the anterior surface of toric IOLs were optimized respectively. The targets was optimized to produce IOLs with -0.26 μm, -0.1 μm and 0 μm spherical aberrations. In the computer optical simulation system, the effect on the modulation transfer function (MTF) was evaluated when spherical and aspherical IOLs were decentrated in the horizontal direction with 0.25 mm, 0.50 mm and 0.75 mm at 3- and 5-mm pupil diameters. The effect on MTF was also evaluated when the two types of IOLs were rotated by 3°, 5° and 10° at 4-mm pupil diameter. Results: At the center, the aspherical toric IOL displayed a better image performance with the increased pupil diameter. When the decentration was 0.5 mm at 3-mm pupil diameters, the imaging quality of the -0.26 μm toric IOL decreased and was worse than that of 0 or -0.1 μm IOL. At 5-mm pupil diameter, when the decentration was 0.75 mm, the MTF of -0.26 μm toric IOL was close to that of the spherical toric IOL, while the MTF of toric IOL with 0 μm and -0.1 μm spherical aberration was slightly better than that of the spherical toric IOL. The MTF of aspherical toric IOLs was better than that of the spherical toric IOL with 3° to 5° rotation, but the curve was equal or even worse than that of the spherical toric IOL with 10° rotation in high spatial frequency. Conclusions: Toric IOLs with a spherical aberration of -0.26 μm have good imaging quality at the center but lower tolerance to decentration. The proper optimization of the spherical aberration of toric IOLs can improve the imaging quality of the model eye, while maintaining the tolerance for decentration and rotation errors. Optimized toric IOLs can attain better optical quality under comprehensive conditions. Key words: cataract; artificial lenses; astigmatism; cornea; decentration; rotation; modulation transfer function; model