What is angiography?
Angiography is an outpatient diagnostic procedure in which a special camera takes photographs of the blood vessels in the retina and choproid, after a dye is injected into a vein. The retina is the light sensitive tissue which lines the back of the eye. The choroid is a layer of blood vessels which lies under the retina. Two different dyes can be injected into the vein: fluorescein or indocyanine green (ICG).
How is angiography done?
Fluorescein and/or ICG dye is injected into an arm vein while the patient sits in front of the camera. Dye travels through the veins and into the arteries, circulating throughout the body. The camera takes a series of photographs as the dye passes through the blood vessels at the back of the eye. No X-rays are involved.
The entire procedure usually takes less than 30 minutes. Because fluorescein dye is removed from the body by the kidneys, the urine turns orange for up to 24 hours. In addition, the skin can turn slightly yellow for several hours. ICG dye is removed from the body by the liver, and no color changes are noticed.
How do fluorescein and ICG angiography differ?
Fluorescein angiography is the best way to examine the blood vessels in the retina, but choroidal vessels are hidden beneath a layer of pigmented cells. ICG angiography is the best way to examine blood vessels in the choroid. The infrared light given off by ICG dye can be seen through the pigment layer.
Unlike fluorescein, ICG requires a special computeriezed camera because regular camera film cannot "see" the ICG dye.
Why is fluoroscein angiography done?
Most angiograms are done with fluorescein. After examining your eyes, the ophthalmologist may order angiography to:
- help diagnose your condition;
- guide laser surgery with pinpoint accuracy;
- monitor the effect of laser surgery;
- follow the course of your condition.
Fluorescein angiography is helpful in evaluating many eye conditions, including:
- diabetic retinopathy;
- macular degeneration;
- retinal vein occlusions;
- macular edema.
Why is ICG angiography done?
The most common reason to do an ICG angiogram is to detect abnormal choroidal blood vessels beneath the retina in people with macular degeneration. Abnormal blood vessels can damage vision by bleeding and scarring. An ICG angiogram can sometimes locate abnormal choroidal vessels better than a fluorescein angiogram. Laser surgery may be recommended if the abnormal blood vessels can be precisely located.
Less common uses for ICG include evaluation of:
- eye tumors;
- inflammation disorders.
What are the risks of angiography?
Although they are not known to cause birth defects, fluorescein and ICG should be used with caution in pregnant women.
Mild allergic reactions such as skin rash and itching are uncommon, and may be treated with oral or injectable antihistamines.
Severe allergic reactions (anaphylaxis) are rare, but may be life threatening.
Some individuals may experience slight nausea during the procedure, but this usually passes within a few seconds. If the dye leaks out of the fragile vein during the injection, some localized burning and yellow staining may occur. This burning usually lasts only a few minutes, and the staining will go away in a few days.
ICG dye contains iodine. Severe allergic reactions are possible in people who are allergic to iodine. You must inform your ophthalmologist if you think you may be allergic to compounds that contain iodine, including X-ray dyes and shellfish.