Choroidal microvascular repair after argon laser photocoagulation. Ultrastructural observations.

Acute laser injury to the tapetum of the feline retina produces thrombosis of the choriocapillaris. Early changes are characterized by the appearance of platelet-fibrin thrombi within capillary loops and disruption of endothelial integrity. By 4 days, thrombi have disappeared, and the endothelium shows regenerative changes. No endothelial cell mitotic activity is seen. The endothelial cytoplasm becomes plump, and there is a loss of the fenestrations adjacent to Bruch's membrane. By 10-20 days, the capillary structure shows gradual restoration. At 30 days, endothelial cell fenestrae are clearly evident adjacent to Bruch's membrane. The reparative process in this model appears to evolve as a result of thrombolysis and endothelial cell activation.