Blood staining of the cornea. Light microscopic and ultrastructural features.

Eleven blood-stained corneas were examined by light and transmission electron microscopy at intervals ranging from one month to seven years after initial staining occurred. Blood staining in each case was associated with focal loss of endothelial cells or endothelial degenerative changes and elevated intraocular pressure. Globules of erythrocytic breakdown products penetrated the discontinuous endothelium and intact Descemet's membrane. Large deposits, primarily extracellular, displaced but did not interrupt the stromal lamellae. Keratocytes in blood-stained corneas contained erythrocytic breakdown products and hemosiderin, and were remarkable for extensive degenerative changes in contrast to keratocytes in areas of cleared cornea, which contained smaller amounts of hemosiderin and were relatively normal. After one year, clearing could be seen to involve peripheral and posterior stroma, and to a lesser degree, the anterior stroma. We found no evidence to support the contention that blood-derived macrophages play a role in the clearing of erythrocyte debris. The stereotyped pattern of peripheral, posterior, and anterior stromal clearing observed seems to be consistent with diffusion of hemoglobin breakdown products out of the cornea as the primary mechanism of clearing.