A correlative electron microscopic and freeze-fracture examination of cat corneal endothelial wound repair

Abstract

In an attempt to create a model for sustained corneal edema in humans, the present study has examined wounded cat corneal endothelium. Small central (7 mm) wounds or large 90 percent debridement wounds were created with an olive tipped cannula and corneas sampled from 1 to 75 days post-wounding were processed for light and transmission electron microscopy and freeze-fracture. In small wounds, wound closure was complete by 14 days and corneal edema was absent. During wound closure, leading edge cell membranes had decreased intramembrane particles, numerous vesicle fusion sites and lacked cell junctions. Endothelium behind the wound margin was multilayered with fragmented cell junctions. After wound closure, endothelium returned to the morphology of non-wounded endothelium except that an abnormal posterior collagenous layer (PCL) was present. Wound closure was greatly retarded in large wounds and corneas remained edematous at 75 days. The morphology of the endothelial cells was similar to that in small wounds except for the presence of large multinucleated cells and a thicker PCL. These large wound findings are similar to those observed in chronically stressed dysfunctional human corneal endothelium and in this animal model may represent a similar response to injury.