R ECENT ADVANCES IN RICSID GAS Permeable Contract LENSES

Abstract

RGP contact lenses were first manufactured in the 1970s combining the ability of hard P1A lenses to correct astigmatism and the oxygen permeability of hydrogel contact lenses.

Different materials are used for RGP contact lenses the earliest of which are cellulose acetate butyrate (CAB) and silicon acrylate. Now new fluoropolymers with Dk values as high as 150 are available.

Parameters of RGP contact lenses e.g. lens diameter, thickness, base curve, secondary curves, and different designs are discussed.

Information about corneal topography as an aid to fitting RGP contact lens is mentioned with special emphasis on colour­ coded computerized videokeratography and simulated fluorescein patterns.

RGP contact lenses are usually fit slightly steeper than keratometric readings unlike soft contact lenses, but there is no hard and fast rule for fitting. Fitting of spherical as well as toric RGP contact lenses is discussed and indications of fitting. The most important of which are keratoconus, astigmatism, and after refractive surgery. Evaluation of fitting is discussed especially fluorescein pattern interpretation as a valuable skill necessary for good fitting.