Corneal edema in phakic and aphakic eyes.

Explanations are given for the physiological behavior of the cornea in the phakic and aphakic eye and for a cornea covered by a contact lens that causes epithelial anoxia. The normal, constant hydration of the cornea is a result of active ion transport by the endothelial layer. The hypoxic epithelium under a contact lens produces lactate ion that migrates to the posterior portion of the cornea where it modifies the normal stromal balance between osmotic and inhibition pressures. A consequence of this modification can be corneal swelling. A reduction in cell count of the endothelial layer, together with a possible increase in aqueous humor oxygen tension is believed to be responsible for the smaller amount of swelling caused by epithelial hypoxia in the aphakic eye.