What is Fluorescein Angiography?
Fluorescein is an orange-yellow ophthalmic dye that enhances the visualization of the eye’s tissues. The fluorescein dye is colored yellow-orange. Fluorescein angiography is a procedure where fluorescein dye solution is injected into the arm. The fluorescein dye circulates through the body’s blood vessels and enters the retinal blood vessels in the back of the eye. Fluorescein angiography of the eye allows for assessment of the health of the retina. Photograph images of the retina are taken immediately after the dye is injected into the arm and for up to 10 minutes after. These photographs help the ophthalmologist see the blood vessels and other structures of the retina, as well as the pattern of blood flow in the retina. Fluorescein angiography is a helpful tool in identifying eye diseases such as diabetic eye disease, retinal vascular disease, and macular degeneration.
- Fluorescein angiography is a procedure where a dye solution is injected into the blood vessels of the arm.
- Fluorescein angiography is performed to photograph the retina (back of the eye) and assess its blood flow.
- Abnormal fluorescein angiography can help to diagnose a wide range of retinal conditions including macular degeneration and diabetic eye disease.
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Understanding Fluorescein Angiography
The purpose of fluorescein angiography is to examine the eye for improper blood flow. It evaluates the blood vessels in the retina and the choroid. A specialized camera captures a photo of the retina, the thin layer that lines the back of the eye and senses light. The fluorescein angiogram is a unique type of retinal imaging because it takes many photos over the course of ten minutes. This time-lapse photo array allows the doctor to see the blood entering the retina, circulating through the retinal arteries and veins, and exiting the retina. Fluorescein dye is intravenously injected into the arm. The eye is photographed immediately as the dye is put into the arm.
Fluorescein angiography side effects include:
- Mild nausea (10% of patients)
- Vomiting (7%)
- Itchy skin or rash at the site of the injection (1%)
- Fainting (1%)
- Anaphylaxis (1/200,000), a very rare but life-threatening allergic reaction
The fluorescein angiography phases categorizes the time elapsed since the fluorescein injection. Each phase can reveal abnormal results.
Fluorescein Angiography Phases:
- Choroidal Filling: 10-20 seconds after injection – background will be bright
- Arterial: 15 seconds after injection – arteries fill with fluorescein dye
- Arteriovenous: 20 seconds after injection – veins begin to fill with fluorescein dye
- Venous: 30 to 60 seconds after injection – veins are completely filled with dye
- Late Recirculation: 40 seconds to 10 minutes after injection – dye exits arteries and veins
Normal Fluorescein Angiography
In a normal retina, the fluorescein dye stays contained within the retinal blood vessels and cannot leak outside of the blood vessel. The dye flows into the eye via retinal arteries, and then flows out of the eye via retinal veins. None of the arteries or veins should be blocked in a healthy eye.
Abnormal Fluorescein Angiography
Abnormal fluorescein angiography results occur if the fluorescein dye leaks outside of the blood vessels, does not enter the arteries, or does not exit through the veins. If any of the blood vessels are unable to carry blood, it can indicate problems with the eye’s perfusion (blood delivery). Low perfusion can cause vision loss and other eye symptoms. The most common way to describe abnormal fluorescein angiography results is through the pattern of fluorescence. Hyperfluorescence means that there is a bright area with excessive amounts of fluorescein. Hypofluorescence means that there are dark black areas that lack fluorescein.
Blocked fluorescence means that fluorescein is present, but it cannot be seen because something is in front of it, blocking it. Anything in front of the retina may block the usual fluorescence. A few examples are a corneal scar, cataract, and vitreous hemorrhage.
Vascular filling defect
A vascular filling defect occurs when fluorescein is not present in either the arteries or veins. The blood vessels do not fill with fluorescein like they should. This can happen when the blood supply to the eye is blocked. For example, vascular filling defects are caused by capillary death from diabetes. It can also be caused by retinal artery occlusions, highly associated with carotid disease and high cholesterol. Retinal vein occlusions, highly associated with uncontrolled hypertension, also cause vascular filling defects. Retinal artery occlusions and vein occlusions can cause permanent, severe vision loss.
Fluorescein leakage occurs when the blood vessels are leaky, and so blood spills outside of the blood vessel walls. This happens if the blood vessels are damaged. Leakage happens in conditions such as severe diabetic eye disease, which causes new leaky blood vessels to grow in the retina. It can also happen in wet macular degeneration.
Staining occurs when fluorescein does not drain out of the eye as expected. It stains the eye for a longer time than it should. This happens if fluorescein is retained in the eye’s tissues. Examples of staining include chorioretinal scars and drusen.
Pooling occurs when there is a part of the retina that accumulates fluorescein dye. Pooling of fluorescein can happen in Central Serous Retinopathy, a condition associated with men who have Type A personalities and stress.
Transmission (Window) Defects
A window defect happens when there is missing retinal epithelial pigment. A window defect makes the choroid, the layer underneath the retina, very bright. Window defects can occur with drusen and geographic atrophy that may be present with macular degeneration.
Autofluorescence occurs if there are bright, shiny areas present in the retina before any fluorescein dye is injected into the arm. This is a natural fluorescence of the retina, without dye, due to hyper-reflective structures. Examples of retinal abnormalities that can cause autofluorescence include optic disc drusen and astrocytic hamartomas.