Biometry of phakic intraocular lens using Scheimpflug photography

PURPOSE: To examine lateral and axial positioning of phakic intraocular lenses (IOLs) with iris fixation in the anterior chamber and to examine short-term stability of the IOL position. SETTING: The Netherlands Opthalmic Research Institute, Amsterdam, the Netherlands. METHODS: Thirty patients participated in the study. Thirty-one eyes were implanted with the 204 type myopia IOL, 14 eyes with the 206 myopia IOL, and 8 eyes with the 203 hyperopia IOL. Scheimpflug slitlamp photographs were made through the optical axis along 4 meridians of the eyes. Ray tracing was used to obtain the lateral and axial position of the IOLs. RESULTS: Centration of the IOL with respect to the pupil's center and the tilt angle of the IOL with respect to the optical axis of the eye were measured. Standard deviation of decentration was 0.21 mm vertically and 0.16 mm horizontally. Standard deviation of tilt was 1.30 degrees vertically and 0.90 degrees horizontally. Tilt and decentration are proportional to each other. Vaulting, the distance between the crystalline lens and the IOL, was constant over a period of 24 months, ranging from 0.2 to 0.8 mm, depending primarily on the radius of curvature of the crystalline lens. A geometric model for this dependence was formulated. CONCLUSION: Phakic IOLs with iris fixation can be positioned in the eye with submillimeter precision. Axial position of iris-fixated phakic IOLs over time is excellent. Axial position and vaulting can be predicted when the radius of curvature of the crystalline lens is known. The IOL behaves as if mounted slightly above a sphere-the anterior surface of the crystalline lens.