The corneal oedema of acute keratoconus is related to a break in endothelial-Descemetic continuity. This break was confirmed by optical and electron microscopical study of an anatomical section taken during a perforating keratoplasty; the methods of repair were studied five months after the incident. The corneal endothelium had almost totally recoversed the surfaces of the detached Descemet's membrane and the posterior surface of the bare corneal stroma. Electron microscopic study tended to indicate that the endothelial repair occurred more by cellular extension rather than mitosis (very flat cells) and showed that the inter-cellular connecting systems (focal tight junctions) were not regular, or even absent altogether, which explained the clinical finding of persistant corneal oedema. The endothelial cells secrete a Descemet neo-membrane over all their area which is more or less complete. They revover an original scarred stroma of fibrocytes of the posterior stroma.