Indocyanine Green Angiography (ICG): is used to evaluate the choroidal circulatory system, just behind the retina. ICG reacts to light with a longer wavelength than fluorescein dye, allowing the doctor to determine exactly where, and if, the vessels are leaking. The ICG dye takes about 15 to 20 seconds to travel through the bloodstream to the eye. The digital photos are interpreted by the physician. If treatment is needed, the photos indicate where the laser treatment needs to be directed. Indocyanine green is often better for studying the deeper choroidal blood vessel layer. Indocyanine green angiography is especially helpful when there is leakage of blood which may make interpretation of fluorescein studies difficult.