ICG is a method of capturing high definition images of the layer of blood vessels behind the retina, called the choroid. During this test, a small amount of fluorescent dye is injected into the blood and then stays in tissues with a higher blood flow like the choroid in the eye for an extended time while a specialized camera captures images of these blood vessels.

This type of imaging is especially important to analyze such diseases as age-related macular degeneration, polypoidal choroidal vasculopathy, and ocular tumors.