Effect of a sulcus-fixated piggyback intraocular lens on negative dysphotopsia: Ray-tracing analysis

Abstract

To use optical modeling to demonstrate how a sulcus-fixated piggyback intraocular lens (IOL) affects negative dysphotopsia. Mayo Clinic, Rochester, Minnesota, USA. Retrospective case series. Optical modeling was performed on 3 patients with negative dysphotopsia who were treated with a sulcus-fixated piggyback IOL. Ray-tracing software was used to simulate peripheral retina illumination preoperatively and postoperatively. Biometric data and ultrasound biomicroscopy images were used to construct eye models. Ray intensities were adjusted for surface reflections and normalized by cosine function to compensate for pupil obliquity at high incident angles. Preoperatively, retinal illumination profiles showed a region of dim or nonilluminated peripheral nasal retina at visual angles of approximately 83 to 95 degrees. A piggyback IOL shifted the iris anteriorly (mean 0.41mm; range 0.37 to 0.47mm) and the primary IOL posteriorly (mean 0.10mm; range 0.05 to 0.19mm) and increased the mean distance between the iris and primary IOL from 0.46mm preoperatively to 0.75mm postoperatively. This increased distance allowed input rays to begin missing the primary IOL at lower incident angles (≥76 degrees) compared with preoperatively (≥84 degrees), resulting in increased illumination of the peripheral retina. Illumination of the peripheral retina, including the preoperative dark area, was increased in 2 patients. The negative dysphotopsia shadow resolved in 2 eyes and was unchanged in 1 eye. In negative dysphotopsia patients, a secondary piggyback IOL allowed additional light to miss the primary IOL and illuminate larger areas of peripheral retina. Increased illumination of the peripheral retina that included the preoperative dark region was associated with improved negative dysphotopsia postoperatively.