Fluorescein angiography of the normal fundus reveals the segmental nature of the choroidal vascular bed. Despite the presence of anatomically demonstrable anastomoses, a segmental distribution is present in vivo up to the choriocapillaris level. Choroidal vascular diseases manifest by localized of diffuse delayed or incomplete filling of the choroid and by the involvement of the overlying retinal pigment epithelium. In the acute phase of choroidal arterial occlusive disease, ophthalmoscopy reveals localized or diffuse edema. Fluorescein angiography of such cases initially shows a delayed perfusion of the involved area followed later on by fluorescein leakage. This late diffusion of the dye is probably related to alterations of the retinal pigment epithelial barrier. The extent of the lesion after resolution of the edema mainly depends on the site and the extent of the occlusion, on the development of collaterals and possibly on the involvement of the choroidal venous circulation. Ophthalmoscopy and fluorescein angiography will reveal localized or diffuse pigmentary changes, sometimes of quite characteristic aspect. This may be associated with local destruction of the choriocapillaris, although normalization of choroidal blood flow may also be observed. Chronic choroidal vascular insufficiency is a possible cause for choroidal sclerosis. Chronic choroidal ischemia is also a possible explanation for peripheral pigmentary changes seen in the elderly.