What is Fluorescein Angiography and when is such a procedure indicated?
Fluorescein angiography is photographic record of fluorescein dye (food coloring) passing through the blood vessels of the film or retina of the eye. The dye fluorescein is water soluble and has the property to fluoresce, that is to emit a specific color of light when stimulated. The dye is injected in an arm vein. This image is captured on film or as a digital image and allows examination of the blood vessels of the retina and choroid as well as structures in the retina.
In addition, this technique may be used to study iris vessels. Indocyanine green dye (ICG) emits in the infrared range and is used to study the choroidal circulation as it allows penetration of the Retinal Pigment Epithelium by light and thereby increases the visualization of the deep, i.e., choroidal circulation.
Side effects are rare but may be severe if an allergy is present. There are few cross allergies with fluorescein angiography but ICG contains iodine and people with an allergy to iodine (shell fish, for example) are at risk for serious reactions and should so inform the ophthalmologist or photographer.
There are many instances when angiography with either fluorescein and/or ICG dye are indicated. The most common are blood flow problems (artery or vein), diabetes mellitus and macular degeneration associated with aging.
How does it help in diagnosing eye diseases?
Everything your eye sees involves the retina, the delicate nerve tissue at the back of the eye that is responsible for receiving optical images. The retina can be affected by many disorders that involve the blood circulation in or under it, such as diabetic retinopathy and macular degeneration. Therefore, learning about the retinal blood vessels is an important step in making an accurate diagnosis of any retinal disorder.
An angiogram is a type of photograph of the retinal blood vessels that helps with these diagnoses. A fluorescein angiogram uses fluorescein dye; it does not use X-rays, radioactive materials, or iodine-based dyes, as do other types of angiograms. The fluorescein dye in the blood vessels allows them to be easily seen in the photographs, so the vessels can be identified and evaluated. Both the presence and absence of dye are clues as to diagnosis and treatment.
How Is the Test Performed?
- First, your pupils will be dilated (enlarged) with eyedrops so the inside (fundus) of your eyes can be photographed. (The dilating effect of the drops may last for a few hours after the test, with your pupils returning to normal size by themselves.
- You will sit in front of a large fundus camera; your chin will be supported and your forehead will be braced against a head support. The technician will take several preliminary pictures before the angiogram test begins.
- A needle is then inserted into a vein in your arm and the fluorescein is injected. The dye quickly travels through your bloodstream, taking only seconds to reach the arteries that supply your eye.
- A series of retinal pictures is then taken in rapid sequence, following the course of the dye. You will hear the camera click and see a flash of light each time a picture is taken.
Are there any side effects or risks?
Fluorescein dye is used every day in thousands of people. It has proved to be useful and essentially safe. However, as with all medications, it sometimes has side effects. Some patients experience nausea or dizziness immediately following the injection, but this feeling goes away in a few minutes.
Occasionally, some dye leaks out of the site where it is injected in the arm, and it can sting and stain the skin yellow. This effect is temporary and not dangerous. Because the body eliminates fluorescein through the kidneys, your urine may appear dark yellow or orange for about 24 hours after the test. Drink plenty of water and don't worry about the color.
You should be aware of the possibility of some more troublesome side effects. A small number of patients are allergic to the dye, and can develop itching and a skin rash. These usually respond to treatment with oral medications such as anti-histamines or steroids. Very rarely, about once in 25,000 individuals, a sudden life-threatening allergic reaction called anaphylaxis can occur, which requires rapid medical treatment to reverse it.
Fluorescein angiography is important and valuable. Without the diagnostic assistance the test provides, several sight-threatening eye diseases could not be properly managed or treated. If fluorescein angiography has been deemed necessary for your care, its potential benefits have been judged to far outweigh the possible risks.