ICG angiography is similar to fluorescein angiography in that it studies blood flow in the back of the eye. The difference is that ICG is focused on the choroidal circulation, or layer of blood vessels beneath the retina itself. Once injected, the dye requires roughly 10-15 seconds to circulate through the body. As the dye enters the blood vessels in one's eyes, a series of photographs are taken to display and record the dye's progress. A filter in the camera allows the dye to "light up", allowing the physician to detect abnormalities in choroidal blood vessels and confirm or diagnose disease processes. ICG is also useful in cases of poor visualization of fluorescein angiography, for example where blood is so diffuse it blocks the visualization of the retina itself.
