It involves injecting a dye and then taking a series of photographs of the vessels of the retina.
The type of dye used is different than the radiologic dye used for heart and brain angiograms. This dye is directly visualized with regular light versus x-rays. It can also be ingested orally but the absorption is not as quick and the results of the test may be compromised.
The test is used in many circumstances in ophthalmology to evaluate patients for macular degeneration, diabetic retinopathy, and many other conditions. The information received from this test can lead to treatment of vision-threatening diseases.