Specular microscopic studies in two patients with traumatic posterior annular keratopathy demonstrated that the endothelial rings consist of disrupted and swollen endothelial cells. The damaged cells were still evident many days after the rings had disappeared. The amount of endothelial cell loss depends on the severity of the injury, and a measurable decrease in cell density occurs only in the more severely injured patients. A physical explanation for the occurrence of these endothelial rings is discussed.