WATER PROPERTIES OF HYDROGEL CONTACT-LENS MATERIALS - A POSSIBLE PREDICTIVE MODEL FOR CORNEAL DESICCATION STAINING

A set of properties of the water contained within hydrogel contact len s materials was determined with the aim of developing a model which wo uld predict the propensity of a hydrogel contact lens material to indu ce corneal desiccation staining. We postulated that materials containi ng a larger proportion of water with the properties of bulk water woul d tend to induce corneal desiccation more readily than materials with the same overall water content but containing a larger proportion of w ater that interacts strongly with the polymer. The water structure [as measured by differential scanning calorimetry (DSC)] and the permeabi lities of water and glucose were determined for a series of commercial hydrogel lenses. Both glucose permeability and DSC measurements are s ensitive indicators of water structure and able to distinguish between various materials. To illustrate the potential of our model, the resu lts of a short-term clinical study are presented. Lower levels of stai ning were noted for a material with a lower glucose permeability and a larger amount of water melting below 0 degrees C than for a control l ens, even though both materials were similar in water content and wate r permeability. Further clinical studies are needed to validate this m odel.