The influence of rotational error and axial shift of toric intraocular lenses on residual astigmatism.

Abstract

Accurate alignment of Toric Intraocular Lens (T-IOLs) in cataract surgery is crucial for good visual outcomes. The purpose of this study was to evaluate the influence of rotation, axial shift and their combined effects on the refractive error and image quality of a wide range of T-IOL powers (from +1.50 D to +6.00 D cylinder) and two pupil diameters (3.34 and 4.44 mm). Numerical ray tracing was utilized to quantify the residual error. Simulated retinal images and Visual Strehl (VS) ratios were calculated to evaluate image quality. First, T-IOL rotation showed better agreement with Holladay's formula than 3.33% rule. Second, axial displacement resulted in acceptable residual cylinder (<0.50 D) across all examined cylinder powers. Third, concerning the combined effects, the influence of axial shift on residual cylinder becomes negligible when rotation errors exceed 2.5°. Fourth, a pupil-dependent nonlinear relationship was noted for image quality caused by both types of misalignment factors. The 3.33% rule was confirmed as a reasonable approximation for the residual astigmatism caused by rotation of T-IOLs. The influence of axial shift on residual astigmatism becomes insignificant when there is also rotation. Image quality studies confirm that 30° of rotation are enough invalidate the compensation benefits of a T-IOLs in comparison with a Spherical Intraocular lens.