Central and peripheral oxygen transmissibility thresholds to\ud avoid corneal swelling during open eye soft contact lens wear

This study was designed to derive central and peripheral oxygen transmissibility\ud (Dk/t) thresholds for soft contact lenses to avoid hypoxia-induced corneal swelling (increased\ud corneal thickness) during open eye wear. Central and peripheral corneal thicknesses were\ud measured in a masked and randomized fashion for the left eye of each of seven subjects before\ud and after 3 h of afternoon wear of five conventional hydrogel and silicone hydrogel contact\ud lens types offering a range of Dk/t from 2.4 units to 115.3 units. Curve fitting for plots of\ud change in corneal thickness versus central and peripheral Dk/t found threshold values of 19.8\ud and 32.6 units to avoid corneal swelling during open eye contact lens wear for a typical wearer.\ud Although some conventional hydrogel soft lenses are able to achieve this criterion for either central or peripheral lens areas (depending on lens power), in general, no conventional hydrogel soft lenses meet both the central and peripheral thresholds. Silicone hydrogel contact lenses typically meet both the central and peripheral thresholds and use of these lenses therefore avoids swelling in all regions of the cornea. ' 2009 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 92B: 361–365, 201