Aberrations induced by pupil center decentrations in customized laser refractive surgery

Abstract

Abstract: : Purpose: To determine the aberrations induced by a static offset of a customized laser refractive surgery ablation due to shifts in pupil center location from when aberrations are measured preoperatively (dilated pupil) to when they are corrected surgically (natural pupil). Understanding and accounting for the aberrations generated by pupil decentrations could improve higher order aberration correction in customized refractive surgery. Methods: Shifts in pupil center relative to the limbus were measured for both dilated (2.5% neosynephrine) and non–pharmacological mesopic conditions in 65 eyes treated with customized LASIK. A Shack–Hartmann wavefront sensor was used to measure each patient's preoperative and 6–month postoperative wave aberration over the dilated pupil. The aberrations that would have been induced by a decentration of a customized ablation were calculated and compared with the 6–month post–op wavefronts (6 mm pupil). Results: The average magnitude of pupil center shift was 0.29 ± 0.141 mm and usually occurred in the inferior–nasal direction as the pupil dilated. Depending on the magnitude of shift, the fraction of the patients' higher order post–op rms wavefront error that could theoretically be due to pupil center decentrations was highly variable with a mean of 0.26 ± 0.20. There was little correlation between the calculated and 6–month post–op wavefronts, most likely due to the fact that pupil center decentrations are only one of several potential sources of post–op aberrations (e.g. biomechanics, healing, imperfect ablations, eye movements, etc.). Conclusions:Measuring aberrations over a neosynephrine dilated pupil and treating them over an undilated pupil usually resulted in a shift of the customized ablation in the superior–temporal direction and an induction of higher order aberrations. Methods referencing the aberration measurement and treatment with respect to a fixed feature will reduce the potential for inducing aberrations due to shifts in pupil center.

Keywords: pupil • refractive surgery • refractive surgery: optical quality