Intraocular Lens Refractive Index and Its Impact on External Surface Reflections

PURPOSE: To determine and compare the origin of the external surface reflections produced by commonly used intraocular lenses (IOLs). METHODS: The specular reflection taking place at the anterior surface of eight types of IOLs (IOL power = 22.00 diopters MD with different refractive indices (RLs), optical design, and ultraviolet and blue tight-filtering function were measured. The experimental set-up included a laser beam tight source (3.5 mW, 532 nm) and a saline-filled model eye containing the IOL to be examined. External surface reflections were measured using a power meter, and the IOL surface reflectance (%) was compared among the eight IOLs investigated. RESULTS: External reflections from the anterior surface of the studied implants increased as the RI of the IOL material increased. The IOL models composed of high RI material (RI = 1.56 +/- 0.02) were found to have a more than threefold higher external surface reflections compared to those with low RI (RI = 1.45 +/- 0.021. Ultraviolet or blue tight-filtering functions showed no significant correlation with the external reflectance. CONCLUSIONS: IOLs with a high RI are associated with external surface reflections that are more than threefold higher than those with lower RI. The "cat's eye" phenomenon seen in pseudophakic eyes by an outside observer strongly depends on the RI, but is independent of the fitter incorporated in the IOL.