The pathology of vitreous hemorrhage. II. Ultrastructure.

We undertook an ultrastructural study of the dual processes of hemolysis and vitreous membrane formation during the resolution of vitreous blood clots in rabbits. Red blood cell degradation began within 24 hours before the onset of the inflammatory response and occurred mainly in the extracellular matrix. Macrophage activity was directed at clearing lysed RBC debris, rather than engulfing whole RBCs. Hemolysis in the vitreous may have been initiated by the unfavorable microenvironment. Two types of vitreous membranes occurred during vitreous clot lysis. Cellular membranes were composed of aggregates of giant macrophages enclosed within a thin collagen sheet. Acellular membranes developed from coaggregated vitreous collagen fibers. A prominent acellular membrane surrounded the blood clot as a pseudocapsule. No fibroblasts or fresh collagen deposition were observed.