Hydrogel contact lens dehydration and oxygen transmissibility

Purpose: Oxygen transmissibility is a key determinant of the physiological response of the cornea to contact lens wear. Because transmissibility is related to hydrogel water content, we conducted a study to determine the change i n water content during lens wear and to quantify the impact any such change would have on transmissibility. Methods: In a double masked clinical investigation, two subjects each wore 17 different pairs of contact lenses. Water content was measured before lens wear at 35°C and immediately after 4 hours of contact lens wear. Contact lens oxygen transmissibilities were calculated on each occasion. Results: The absolute changes in water content for the 17 lenses varied from +0.5% to -5.3%. For some lenses, this change in water content altered the lens oxygen transmissibilities to a clinically significant degree. The changes in water content and oxygen transmissibilities were greatest with FDA Group IV lenses. Conclusions: Dehydration during contact lens wear can alter the oxygen transmissibility of hydrogel lenses, and in some situations, this factor may be clinically significant.