Specific Gravity And Vertical Lens Decentration.

The specific gravity of various rigid gas permeable (RGP) contact lens materials is often an overlooked parameter in RGP fitting and refitting. The purpose of this study was to evaluate the influence of specific gravity on the vertical positioning of two different RGP materials: Boston RXD (Polymer Technology Corp.) and Fluoroperm 60 (Paragon Optical, Inc.). Twenty subjects were fitted with one base curve of RXD material and similar base curve of FP 60 material on their right eyes. Vertical decentration was measured using a video biomicroscope. It was concluded that the Boston RXD lens decentered more inferiorly than the Fluoroperm 60 lens. Practitioners should consider specific gravity as an important parameter in the fitting of RGP lenses.