APOPTOSIS IN THE RAT CORNEAL EPITHELIUM DURING REGENERATION - A TRANSMISSION ELECTRON-MICROSCOPIC STUDY

In the present transmission electron microscopic study, regenerating r at corneal epithelium is examined at three different time points after chemical abrasion. Four days after the initial injury classical signs of regeneration are observed. At day 6 regeneration is less pronounce d and epithelial differentiation dominates the morphological picture. Many basal cells are swollen and single electron-dense basal cells hav e a shrunken morphology (dark cells). Intercellular cytoplasmic sacs a re common and some appear to be phagocytosed. At day 8 there are no si gns of regeneration and neither dark cells nor swollen cytoplasmic sac s are seen. No signs of intraepithelial inflammation are seen at any t ime. ''Odland''-like granules, which possibly play a role in epithelia l desquamation, occur suprabasally in large numbers at all time points . We believe the simultaneous presence of dark cells and phagocytosis at day 6, without signs of inflammation, indicates ongoing apoptosis. Intraepithelial cell loss might explain the discrepancy between an inc reased proliferation rate and the absence of hyperplasia which has bee n reported at this time point.