 One diagnostic method for the confirmation of CRAO is Fluorescein angiography, it is used to examine the retinal artery filling time after the fluorescein dye is injected into the peripheral venous system.In an eye with CRAO some branches of the retinal artery may not fill or the time it takes for the branches of the retinal artery to fill will be increased, which is visualized by the leading edge of the fluorescein moving slower than normal through the retinal artery branches to the edges of the retina.Fluorescein angiography can also be used to determine the extent of the occlusion as well as classify it into one of four types non-arteritic CRAO, non-arteritic CRAO with cilioretinal artery sparing, transient non-arteritic CRAO and arteritic CRAO.