Water diffusion in worn Etafilcon A contact lenses

In contact lens (CL) wear, it is important to manage CL dehydration to prevent dryness and associated symptoms. The present study is aimed at comparing the dehydration kinetics of unworn Etafilcon CLs hydrated with saline solution versus worn CLs hydrated by tears. At 36◦C and 60% relative humidity, the dehydration kinetics of the CLs were analyzed using an in vitro gravimetric method. A model based on the Fick diffusion equation was employed to deduce a water kinetics coefficient. Unworn CLs exhibit a non-Fickian dehydration behavior, while in the CLs just removed from the eye after five minutes of wear and hydrated by tears, there is a change in the water diffusion within the polymeric matrix showing a tendency towards free diffusion. This variation is accompanied by a noticeable dehydration of the worn CL. After two hours of wear, the same effect was observed in approximately half of the samples, but it is not observed if the CL is subsequently incubated in saline solution.