An ICG Angiography is a type of blood flow study that is used particularly to study deep blood vessels under the retina. It uses a particular type of dye (ICG – or indocyanine green) that is typically injected into an arm vein. The dye eventually reaches blood vessels in the eye and fluoresces when photographed with an infrared camera. These wavelengths are able to reach to deep layers in the retina, so that these deep blood vessels can be seen. This can be useful for studying abnormal vessels in conditions such as macular degeneration, among others.