The cellular response to blood in the vitreous: an ultrastructural study

The cellular response to whole blood injected into the vitreous cavity of rabbits was studied by transmission and scanning electron microscopy. Inflammatory cell invasion was slow to commence (2--3 days) and was predominantly mononuclear. Although firmly established by 6 days, the cell response remained low-grade with a high proportion of giant macrophages. In addition, multinuclear giant cells were observed, even as long as 18 mth after blood injection into the vitreous, and their formation appeared to result from the fusion of young cells with older macrophages. Phagocytosis of red cells by macrophages was frequently observed, but the major pathway for red cell degradation appeared to be extracellular haemolysis. In general, the cell response was similar to that in a "low-turnover" granuloma, and it is suggested that this atypical response to blood deposits may be due to the unusual nature of the connective tissue matrix of the vitreous.