Kombination aus Dezentrierung und Verkippung der Linse im phaken und pseudophaken Auge – optische Simulation von Defokus, Astigmatismus und Coma [Combination of lens decentration and tilt in phakic and pseudophakic eyes-Optical simulation of defocus, astigmatism and coma]

Background and purpose. The effect of lens decentration and tilt on retinal image quality has been extensively studied in the past in simulations and clinical studies. The purpose of this study was to analyze the effect of combined lens decentration and tilt on the induction of defocus, astigmatism and coma in phakic and pseudophakic eyes. Methods. Simulations were performed with Zemax on the Liou-Brennan schematicmodel eye. Based on the position of the gradient lens the image plane was determined (best focus). The lens was decentered horizontally from -1.0mm to 1.0mm in steps of 0.2mm and tilted with respect to the vertical axis from -10 degrees to 10 degrees in steps of 2 degrees (in total 121 combinations of decentration and tilt). For each combination of decentration and tilt defocus, astigmatism (in 0/180 degrees) and horizontal coma was extracted from wave front error and recorded for a pupil size of 4mm. After replacement of the gradient lens with an aberration correcting artificial lens implantmodel with the equatorial plane of the artificial lens aligned to the equatorial plane of the gradient lens, the simulations were repeated for the pseudophakic eye model. Results. For the lens positioned according to the Liou-Brennan schematic model eye the simulation yielded a defocus of 0.026 dpt/-0.001 dpt, astigmatism of -0.045 dpt/-0.018 dpt, and a coma of -0.015 mu m/0.047 mu m for phakic/pseudophakic eyes. Maximum values were observed for a horizontal decentration of 1.0mm and a tilt with respect to the vertical axis of 10 degrees with 1.547 dpt/2.982 dpt for defocus, 0.971 dpt/1.871 dpt for astigmatism, and 0.441 mu m/1.209 mu mfor coma. Maximum nega-tive values occurred in phakic/pseudophakic eyes with -0.293 dpt/-1.224 dpt for defocus, for astigmatism -0.625 dpt/-0.663 dpt and for coma -0.491 mu m /-0.559 mu m, respectively. Conclusion. In this simulation study the effect of a combination of lens decentration in horizontal direction and tilt with respect to the vertical axis on defocus, astigmatism and horizontal coma was analyzed. The results may help to describe in clinical routine if with a decentered or tilted artificial lens implant the postoperative refraction does not match the target refraction or the resulting astigmatism after cataract surgery is not fully explained by measurement of corneal astigmatism.