Morphologic and Functional Evaluation of the Human Corneal Endothelium

Abstract

The corneal endothelium maintains corneal deturgescence, apparently by a pump- leak mechanism in which the cellular monolayer constitutes a leaky barrier to fluid movement into the cornea and actively pumps ions out of the cornea. The clinical status of these functions can be estimated by measuring the endothelial permeability to fluorescein (proportional to the leak) and the rate of stromal deswelling after hypoxia-induced edema (proportional to the pump minus the leak). The test is conducted by measuring stromal and aqueous humor fluorescence and corneal thickness at intervals over a 7-hour period after first instilling topical fluorescein and inserting an aphakic soft contact lens for 2 hours. Morphologic evaluation is obtained from endothelial photographs by measuring the cell density, cell size distribution, and percentage of hexagonal cells. Functional abnormalities often reflect morphologic abnormalities. The rate of stromal deswelling is decreased in the eyes of individuals with diabetes mellitus, Fuchs’ dystrophy, penetrating keratoplasty, and contact lens wear. Morphologic abnormalities have been demonstrated in the corneal endothelial cells of patients with all these conditions.