[Experimental retinal branch vein occlusion. 4. Pathological changes in the middle and late stage]

Retinal branch vein occlusion in macaca monkeys (Macaca irus) was produced by dye laser photocoagulation, and observed histopathologically from five days to one year after photocoagulation. Ten days later, retinal edema and hemorrhage observed at an early stage gradually decreased. Two weeks later, capillary bed closure areas were observed in fluorescein angiography. The capillary closure was not reversible when disturbance of the retinal circulation continued for more than three or four days after photocoagulation. Three months later, dry retina was observed in the capillary bed closure areas. One year later, the retina was severely degenerated and thinned. In these retinal areas, capillary lumens observed microscopically were occluded by cellular components. Sheathing of large veins was observed in these retinal areas. The walls of these large veins were thick and fell into hyaline degeneration. Their lumens were narrowed or obstructed. During the period of observation, retinal neovascularization was not observed.