Fundus photography (left) and fluorescein angiography (right) can document areas of vascular leakage, nonperfusion, and neovascularization. Fluorescein, a yellow dye that fluoresces under cobalt-blue light, is injected intravenously. A series of photographs is taken as the dye courses through the retinal vasculature. Fluorescein angiography is useful in guiding laser surgery for macular edema. Note the leaky microaneurysms (arrows) in this patient with CSME.