Oxygen permeability of hard gas permeable contact lens materials

Oxygen transmissibility (Dk/L) data of contact lenses enables prediction of the ocular response during wear. However, there has been difficulty in relating the data from highly permeable rigid lens materials to models predicting corneal swelling based upon the Dk/L of soft lenses. We have examined the methodology used to determine the oxygen permeability (Dk) of hard gas permeable (HGP) materials, and have applied a measurement technique that overcomes certain deficiencies of previous methods. A representative range of HGP and hydrophilic lens materials was measured. The Dk values reported here for hydrophilic materials are in close agreement with those published elsewhere. However, the Dk values of HGP materials were found to be substantially less than those reported previously, although the relative ranking appears to be independent of measurement technique. Possible explanations of these findings are presented.