Experimental retinal branch vein occlusion in the monkey. Histopathological and ultrastructural studies.

Light and electron microscopical studies of monkey retinae after experimental branch vein occlusion by argon laser reveal that the immediate reaction in the corresponding region is one of capillary engorgement and dilatation followed by oedema (intra- and extracellular), and plasma leakage as shown by intravenous injection of horseradish peroxidase. Vascular stasis is characterized by packing of erythrocytes in the capillary lumen, early thrombus formation, and focal haemorrhages. Progressive degenerative changes in the endothelium and pericytes are seen in specimens taken a few hours to a few days after occlusion; within 3 to 4 weeks many vessels in the occluded region are reduced to basement membrane "ghosts" and the lumen and the cellular lodges of some vessels are subsequently invaded by proliferating glia, thus producing permanent capillary closure.