Corneal response to different oxygen levels during extended wear

In this study we explored the relationship between hypoxic exposure level and corneal response by assuming that the partial pressure of oxygen (PO2) under a contact lens during eye closure is directly related to oxygen transmissibility (Dk/L). To study this relationship, we monitored a group of subjects who wore RGP lenses of various Dk/L values on an extended wear basis. The results revealed that as Dk/L increases, there is a substantial decrease in overnight corneal edema and epithelial microcysts. However, other responses seemingly related to purely mechanical properties (e.g., lens adherence, corneal topographical changes, and 3-9 limbal superficial punctate keratitis) appear to be independent of Dk/L. Results also suggest that sufficient PO2 levels under a contact lens can minimize endothelial morphological changes associated with hypoxia. We conclude that metabolically driven complications accompanying RGP extended wear can be substantially eliminated with lenses having Dk/L values of 80 x 10(-9) (cm x mL O2)/(sec x mL x mm Hg) or greater.