Measuring corneal recovery from osmotic and anoxic stress.

Halos indicate an important change in vision performance which can occur in contact lens wearers. Experimentally, halos occur when the cornea id deprived of atmospheric oxygen or bathed with hypotonic solutions. Pachometry is the accepted technique for measuring changes in the cornea, yet there is little evidence that measurement of overall corneal thickness is a sensitive indicator of structural changes in the epithelium, such as those causing halos. There is a need for a technique which is responsive to changes in the epithelium. This paper describes a new technique for quantifying changes in the epithelium by measuring halo brightness. Halos were produced by osmotic and anoxic stress, and recovery was monitored using measurements of corneal thickness and halo brightness. We found that the time course of halo recovery could be measured successfully on a naive subject. The technique provides information not available from pachometry and should be of considerable value in studies on the human cornea of factors which alter the optical integrity of the epithelium.