Sliding of epithelium in experimental corneal wounds. A scanning electron microscopic study.

The morphological changes in the rabbit cornea due to a linear wound and a central keratectomy and its reepithelization were examined under the scanning electron microscopy. After the rounding off and retraction of the edges of the wound, during the first 6 h, the stroma was infiltrated by leucocytes. First of all the superficial epithelial cells migrated over the edges of the wound to protect the exposed cleft in the tissue. After 15 h the basal epitheliel cells sent pseudopodia-like processes of varying lengths into the wound area. The migrating cells were mainly flat. During this phase the primary migration of the basal epithelial cells was followed by subsequent cell layers. In the migration, three types of cells can be distinguished: 1. very flat cells with smooth edges without microprojections, which adapt their shape to the clefts in the damaged stroma, 2. flat cells with considerably folded plasma membrane on the cell surface giving a coral-like appearance, 3. cells with voluminous cytoplasmic processes. The rapidly sliding epithelium covered the defect with star shaped growths so that after only 48 h a nearly complete closure of the wound was achieved. After 96 h the deep wound was completely covered by epithelium. The epithelial cells did not yet possess their original surface structure in that they had demonstrably fewer microvilli and microplicae than normal. Only after five days at the earliest could the normal surface relief be seen. The surface cells were predominant in the first stage of the healing process and the basal cells only in the second stage.