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Hydrogel contact lens dehydration and oxygen transmissibility
1Eurolens Research, Department of Optometry and Neuroscience, University of Manchester Institute of Science and Technology, United Kingdom.
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 in 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 degrees 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.