Surface ultrastructure in alkali-burned rabbit corneas.

The scanning electron microscope was used to follow morphologic events after alkali burn of rabbit corneas. Immediately after a burn there was extensive destruction and shrinkage of the epithelial cells. In subsequent healing, the regenerated superficial cells were morphologically abnormal and possed multiloculated cysts; three months later the normal polygonal packing of cells was not observed. Although the shape of these cells was irregular, microprojections were present on the cell surface. Basal cells were usually observed at the edge of an epithelial defect, an area where the epithelium was easily detached from the basement membrane. In long-standing epithelial defects, the basement membrane became eroded in a spot-like manner after about two weeks. Eventually, when a frank stromal ulcer had formed, bundles of collagen fibrils were visible in a meshwork-like fashion. These changes did not seem to be caused by the direct action of alkali but rather by latent secondary factors that took days or weeks to activate.