This is a diagnostic test performed by retina specialists to evaluate circulatory problems in the retina. Fluorescein is a harmless yellow dye that has the unique property that it glows under a blue/black light. This dye can be injected into the arm and introduced into the blood stream. As the dye works its way into the eye, photographs of the retina are taken every few seconds to look for leaking areas or structural problems. This is particularly useful in detecting vessel leakage from macular degeneration and diabetic retinopathy, with the results helping to guide treatment. While this test is relatively innocuous, a small percentage of people have a temporary allergic reaction to the injection.