Morphologic observations on experimental subretinal neovascularization in the monkey

Subretinal neovascularization is a poorly understood and potentially disastrous feature of many eye diseases. We used light and electron microscopy to study the sequence of events that lead to the formation of new vessels after laser photocoagulation of the retina and choroid of primates. In this animal model there is a rapid development of new blood vessels; one day after photocoagulation, endothelial cell degeneration and thrombus formation were observed in the capillaries, venules and arterioles of the choroid around the center of the lesion. Re-endothelialization began in some thrombosed choroidal vessels, with migration of the activated endothelial cells within the old basement membrane. Two days after photocoagulation, re-endothelialization was observed in almost all thrombosed choroidal vessels, and the initial stage of the endothelial cell budding was observed in the pre-existing choroidal vessels; this was especially prominent in venules with pericytes. Three days after photocoagulation, not only the endothelial cells in pre-existing vessels but also those in re-endothelialized vessels showed budding and lumen formation. The lumen of vessels was formed by the budding of adjacent endothelial cells that were coupled by transient intercellular junctions. Mitotic figures were frequently found in the endothelial cells distal to the growing tip. Five to eight days after photocoagulation, many new vessels extended into the subretinal space.