Choroidal vascular repair: scanning and transmission electron microscopy.

Repair of the choroidal vasculature following laser photocoagulation in the rat was examined with vascular casts and correlated with observations on thin-sections. The regenerative process began at the periphery of the damaged area, starting from the surviving choriocapillaris and venules, and proceeding towards the center by means of recanalization of damaged vessels and growth of new ones. In small healed lesions the capillary bed was re-formed. It resembled the adjacent undamaged choriocapillaris morphologically but appeared to be less dense than the intact choriocapillaris when examined by scanning microscopy. In large lesions the capillary bed was re-formed at the periphery but not at the center. Also present at the edges of the large lesions were groups of new vessels which, when observed by scanning microscopy, appeared to extend in two directions; towards the subretinal space and towards the choroidal network. Another aspect of the repair process was the simultaneous occurrence of new vessel growth and capillary regression, which was observed both at the level of the choriocapillaris and at the foci of new vessels.