by Wendy Strouse Watt, O.D.
What is Fluorescein Angiography?
Fluorescein angiography is a test which allows the blood vessels in the back of the eye to be photographed as a fluorescent dye is injected into the bloodstream via your hand or arm. It is particularly useful in the management of diabetic retinopathy and macular degeneration. The test is done to help the doctor confirm a diagnosis, to provide guidelines for treatment, and to keep a permanent record of the vessels at the back of the eye. Fluorescein sodium is a highly fluorescent chemical compound that absorbs blue light with fluorescence. Although commonly referred to as fluorescein, the dye used in angiography is fluorescein sodium, the sodium salt of fluorescein. A common misconception is that it is a 'vegetable dye' rather than a synthetic.
How Is The Procedure Done?
The pupils will be dilated with eye drops and the yellow dye is injected into a vein in your arm. During the injection, there can be a warm feeling or a hot flush can be experienced. This only lasts seconds and then disappears. Following the injection, photos are taken quickly over a period of about 60 seconds as the dye enters the vessels at the back of your eye. The lights flashed at you may appear bright but will NOT damage your eyes. It is common for the skin to be pale yellow and the urine colored fluorescent yellow after the procedure and these may take two days to wear off.
Are There Possible Adverse Reactions?
Fluorescein angiography is an invasive procedure. Adverse reactions occur in 5 to 10 percent of patients and can range from mild to severe. Nausea and occasional vomiting are the most common reactions and require no treatment. These mild reactions seem to be related to the volume of dye and rate of injection, but no studies have yet been done to substantiate that possibility. More severe reactions are rare, but include hives, laryngeal edema (swelling of the larynx), bronchospasm (difficulty breathing), syncope (passing out), anaphylaxis (allergic reaction that requires a shot of medicine to counter act it), myocardial infarction and cardiac arrest (heart attack and heart stoppage). Although there are no known risks or adverse reactions associated with pregnancy, most practitioners will avoid performing fluorescein angiography in pregnant women, especially in their first trimester. Extravasation (the dye is forced from the blood vessel into surrounding tissue) of fluorescein dye during the injection can be a serious complication of angiography and can be quite painful due to the pH. Sloughing off of the skin, localized necrosis (skin death), subcutaneous granuloma (a tumor made up of granulation tissue resulting from injury or inflammation or infection) , and toxic neuritis (inflammation of nerves, with pain, loss of reflexes, and atrophy of the affected muscles) have been reported following extravasation of fluorescein. With proper injection technique, these complications can usually be avoided. Although life-threatening reactions during angiography are rare, the angiographic facility should be properly equipped and prepared to manage serious reactions to the procedure. It is generally recommended that a physician be present or available during angiography.
Why Is The Procedure Done?
In macular degeneration, angiography is useful in identifying the presence and location of subretinal neovascularization (new blood vessels growing under the retinal which will leak and bleed). Post-treatment angiograms also check how effective the laser treatment was. Some retinal conditions exhibit a characteristic patterns of fluorescein staining which can confirm the diagnosis. Stargardt's Disease is an example, showing a nothing in the choroid and a central bulls-eye staining pattern in the macula. With photodynamic therapy (PDT), pre-treatment angiograms are used to determine the location and size of the areas to be treated. The actual size of the area can be measured and the appropriate spot size of the PDT laser can be calculated.
What Does The Doctor Look For?
There are several phases of the angiogram--the early phase, the mid phase, and the late phase. The early phase of the angiogram has several distinct circulation phases that are useful for interpreting the results--the choroidal flush, the arterial phase, the arteriovenus phase, and venus phase. In a normal patient, the dye appears first in the choroid, a layer of the eye outside the retina, in 10-12 seconds. The major choroidal vessels are impermeable to fluorescein, but the choriocapillaris (the internal layer of the choroid that is full of closely packed blood vessels) leaks fluorescein dye freely into the extravascular space, outside the blood vessels. In the choroidal flush, there is very little detail because retinal pigment epithelium (RPE) acts as an irregular filter that partially blocks the view of the choroid. The retinal arterioles typically fill a second or two after the choroid. Complete filling of the retinal capillary bed follows the arterial phase and the retinal veins begin to exhibit filling. Complete filling of the veins occurs over the next ten seconds with maximum vessel fluorescence occurring within 30-35 seconds after injection. The mid phase, also known as the recirculation phase, occurs about 2 to 4 minutes after injection. The veins and arteries remain roughly equal in brightness. The intensity of fluorescence decreases slowly during this phase as much of the fluorescein is removed from the bloodstream and goes through the kidneys. The late or elimination phase shows the gradual elimination of dye from the retinal and choroidal vasculature. Any other areas of late hyperfluorescence (brightness) may indicate the presence of an abnormality.
Interpretation of the abnormal angiogram relies on the identification of areas that exhibit hypofluorescence (darkness) or hyperfluorescence (brightness). These are descriptive terms that refer to the time specific, relative brightness of fluorescence in comparison with a normal study.
What is Indocyanine Green?
ICG (indocyanine green) is a green dye that fluoresces with invisible infrared light. Fluorescein angiography is most useful for studying the retinal circulation, whereas ICG is better suited for studying the deeper choroidal circulation. Fluorescein angiography is most frequently used for evaluation of patients with diabetic retinopathy, occlusive diseases such as retinal vein and arterial occlusions, and evaluation for wet macular degeneration. ICG angiography is most frequently used when blood is present in the macula of patients with the wet form of macular degeneration because this may make interpretation of fluorescein angiography more difficult.