Deswelling of the cornea after hypoxia.

Central corneal thickness changes were monitored in nine subjects who wore low water content hydrogel lenses of varying thickness for 3 h in the open and closed eye conditions. At the end of 3 h of lens wear, corneal deswelling to prelens thickness for the different levels of hypoxia was determined by pachometry performed every 5 min for the first 30 min, every 10 min for the next 40 min, and every 15 min thereafter. Examination of the individual deswelling profiles indicates (1) a biphasic response in those with corneal edema greater than 14%, and (2) a large portion of the deswelling occurred during the first 30 min, followed by a more gradual rate until baseline was reached. Small amounts of corneal edema (less than 5%) required up to 25 min to return to baseline, whereas 6 to 15% required 30 to 70 min, and 20% required 95 min. The time taken for the cornea to deswell to baseline was linearly related to the amount of corneal swelling (r = 0.88; p less than 0.0001).