Glucose and water diffusion kinetics study in a fluorosilicone acrylate contact lens material by positron lifetime spectroscopy.

A comparative study of water and glucose sorption in a rigid gas-permeable contact lens polymer, Fluoroperm 92, has been carried out using positron annihilation lifetime spectroscopy, gravimetric analysis and refractive index measurements. The water sorption in FP92 is non-Fickian, whereas for glucose sorption it changes to Fickian. Glucose molecules reduce the interaction of water molecules with the polymer, resulting in more free water than bound water. It is observed that lenses which contain more bulk-water are prone to lens dehydration and corneal desiccation. The present results indicate that, in case of diabetics, as the glucose level increases in the aqueous humor, there would be more free water than bound water, which increases the propensity for corneal desiccation. The change in refractive index with increase in glucose content indicates decrease in optical transparency of the material.