Carbon dioxide permeability of contact lens materials

Abstract

A dual chamber technique for measuring the carbon dioxide transmissibility of contact lenses is described, together with a method of calculating carbon dioxide permeability. The oxygen and carbon dioxide permeabilites of three hydrogel, 26 RGP, and one silicone elastomer materials were determined. The carbon dioxide permeability of hydrogels was found to increase with water content. Whereas the ratio of carbon dioxide permeability to oxygen permeability is 21:1 for hydrogels, it was found to be only 7:1 for RGP materials and 8:1 for the silicone elastomer. Thus, for a hydrogel and RGP contact lens of the same oxygen transmissibility, the carbon dioxide transmissibility of the hydrogel lens will be three times that of the RGP lens. This data will assist modelling of the ocular response to corneal acidosis resulting from retardation of carbon dioxide efflux by contact lenses.