Fluorescein angiography
Fluorescein angiography (FA), fluorescent angiography (FAG), or fundus fluorescein angiography (FFA) is a technique for examining the circulation of the retina and choroid (parts of the fundus) using a fluorescent dye and a specialized camera. Sodium fluorescein is added into the systemic circulation, the retina is illuminated with blue light at a wavelength of 490 nanometers, and an angiogram is obtained by photographing the fluorescent green light that is emitted by the dye. The fluorescein is administered intravenously in intravenous fluorescein angiography (IVFA) and orally in oral fluorescein angiography (OFA). The test is a dye tracing method. The  fluorescein dye also reappears in the patient urine, causing the urine to appear darker, and sometimes orange. It can also cause discolouration of the saliva. Fluorescein angiography is one of several health care applications of this dye, all of which have a risk of severe adverse effects. See fluorescein safety in health care applications. Fluorescein angiography does not involve the use of ionizing radiation. Fluorescein angiography was pioneered by German ophthalmologist Achim Wessing, who published his findings in 1969. Normal circulatory filling. "times are approximate" Fluorescein enters the ocular circulation from the internal carotid artery via the ophthalmic artery. The  ophthalmic artery supplies the choroid via the short posterior ciliary arteries and the retina via the central retinal artery, but the route to the choroid is typically less circuitous than the route to the retina. This accounts for the short delay between the "choroidal flush" and retinal filling. Pathologic findings. Pathologic changes are recognized by the detection of either hyperfluorescence or hypofluorescence. Causes of hyperfluorescence: Causes of hypofluorescence: Fluorescein angiography is used by physicians specializing in the treatment of eye diseases (ophthalmologists) to evaluate the vasculature of the retina, choroid, optic disc, and iris. Among the common groups of ophthalmologic  disease, fluorescein angiography can detect diabetic retinopathy (neovascularization), vein occlusions, retinal artery occlusions, edema of the optic disc, and tumors. Additionally, the transit time (the period between injection of the dye and when it appears in the examined blood vessels) can provide an objective measurement of the rate of blood flow through the imaged blood vessels.