(437b) Determination of Oxygen Diffusivity(D) and Solubility(k) of a Highly Oxygen-Permeable Soft Contact Lens

The oxygen permeability(Dk) of a contact lens need to be maximized to provide sufficient supply of oxygen to an avascular cornea. However, the development of new materials for contact lens requires the information of even more fundamental properties, such as oxygen diffusivity(D) and solubility(k). The oxygen diffusivity, D, is sensitive to the detailed path(s) by which oxygen migrates through the lens, and is, therefore, quite sensitive to microstructure. On the other hand, oxygen solubility, k, is sensitive primarily to the relative composition of constituents of the lens material.

In this work, an apparatus was designed for determination of D and k of a soft contact lens in the same experiment. The dynamic response of the system to perturbation in oxygen concentration was recorded using the electrolytic-cell-based polarographic technique. The experiment was carried out at tear film temperature (35°C) under limiting current conditions. A mathematical model was devised using asymptotic analysis for effective fitting of the experimental data. We found that oxygen diffusivity of a silicone-hydrogel contact lens is about the same as that of conventional hydrogel lens, however, oxygen solubility is higher by a factor of 3-5 relatively. Thus, higher oxygen solubility is mainly responsible for high Dk of silicone-hydrogels. The determination of D & k has been carried out for the first time for modern high-Dk silicone-hydrogel contact lenses. The information about these fundamental properties will contribute to the design of next generation contact lens materials.