Corneal re-epithelialization from the conjunctiva.

After debridement of the entire corneal epithelium, epithelial cells of conjunctival origin cover the exposed corneal surface. Four to five weeks later, these cells undergo a morphologic transformation to normal-appearing corneal epithelium. To study this transformation the entire corneal epithelium was removed from rabbits with the use of n-heptanol, after which the histologic appearance of and the number of goblet cells in the regenerated epithelium were noted. Five stages of transformation were seen. Immediately after healing, the epithelium consisted of one to two squamous cell layers with no goblet cells apparent at the light microscope level (stage 1). In the following weeks goblet cells appeared at the limbal edge of the cornea (stage 2), reached a uniform distribution across the cornea (stage 3), and subsequently receded toward the limbus (stage 4), leaving an epithelium with normal corneal morphologic appearance (stage 5). To see if there was an ongoing centripetal cell migration from the conjunctiva across the cornea after initial healing, the central corneal epithelium was isolated from the periphery by a ring of glue. Such isolation resulted in a thinning of the central epithelium and a thickening of the peripheral epithelium. These studies suggest that (1) the transformation into corneal epithelium lags behind defect closure by 4 to 5 weeks, (2) goblet cells do not initially migrate as recognizable cells, and (3) there is a continuous centripetal cell motion even after the initial defect closure is accomplished.