Choroidal reaction and vascular repair after chorioretinal photocoagulation with the free-running neodymium-YAG laser.

The morphologic effects of the neodymium-YAG laser working in the free-running mode on the choroid of pigmented rabbit eyes have been studied by electron microscopy. Two different mechanisms closing the choroidal vessels were found. The larger vessels of the vascular lamina were closed by platelet aggregation, while within the choriocapillaries a network of fibrin could be observed. The endothelial cells of the vessels were found to be damaged in capillaries as well as in the larger vessels. Within the irradiated area, a revascularization process takes place, expanding from the border towards the center. The process begins a few days after treatment and continues for more than four months. The process of neovascularization is described in detail. Beside fibroblasts, cells could be found that were active in producing elastic fibers.