Electron microscopy of corneal wound healing

Abstract

Perforating incisions about 1·5 mm in length were made in the center of rabbit corneas. The eyes were enucleated after various periods, and the corneal wound was studied by light and electron microscopy. The cuts showed excellent apposition anteriorly, and were closed posteriorly by a fibrin clot. The epithelium had started proliferation by 3·5 hr, reaching its peak in 2 days, and a large epithelial plug was formed. The keratocytes in a 300 μm zone adjacent to the cut degenerated and disappeared. Intact peripheral keratocytes migrated toward this acellular zone and underwent mitosis. They reached the cut edge after 2 days, and showed characteristics of fibroblasts. After 3 and 4 days the epithelial plug regressed, and fibroblasts entered the anterior cut in large numbers, forming collagen fibers. However, fibroblasts did not enter the posterior part of the cut. Intact endothelial cells remained very near the cut edge of Descemet's membrane, and began proliferating by 24 hr. Regenerating endothelial cells extended on the posterior surface of the fibrin clot toward the center, covering the wound completely in 4–8 days. These cells were separated from the stroma by the fibrin mass. In late stages, they formed a mass of endothelial cells which filled the posterior portion of the incision. A normal endothelium and a new Descemet's membrane formed on the posterior surface of the mass between the cut edges of the old Descemet's membrane. Finally, the cellular elements in both anterior and posterior portions of the cuts were reduced in number until the border of the scar could not be detected. It is concluded, therefore, that the corneal healing process is different in the anterior and posterior portions of the incision, and that both epithelial cells and fibroblasts participate in healing of the anterior portions, while only endothelial cells play a role in the most posterior portion of the corneal wound.