Retinal Diagnostic Testing
Ophthalmic Fluorescein and Indocyanine Green Retinal Angiography
Fluorescein and indocyanine green (ICG) angiography are diagnostic tests which use special cameras to photograph the structures in the back of the eye. These tests are very useful for finding leakage or damage to the blood vessels, which nourish the retina. In both tests, a colored dye is injected into a vein in the arm of the patient. The dye travels through the circulatory system and reaches the vessels in the retina and those of a deeper tissue layer called the choroid (see Figure below). Neither test involves the use of X–rays or harmful forms of radiation.
Fluorescein is a yellow dye that glows in visible light, using special filters. Indocyanine is a green dye that fluoresces with invisible infrared light; it requires a special digital camera sensitive to these light rays.
Why Is Eye Angiography Performed?
Both tests can help retina specialists diagnose and evaluate specific eye diseases. Fluorescein dye is best for studying the retinal circulation while indocyanine green is often better for studying the deeper chorio-capillary layer. Certain eye disorders, such as diabetic retinopathy and retinal vascular occlusive disease affect primarily the retinal circulation and are usually imaged with fluorescein dye. In other disorders, such as age-related macular degeneration, where leakage is from the deeper choroidal vessels, both tests may be useful. Indocyanine green angiography is especially helpful when there is leakage of blood that can make interpretation of fluorescein studies difficult.
When abnormal vessels or leakage is identified with an angiogram, laser treatment or pharmacological therapies may be indicated to treat vision loss. The tests can also be useful for following the course of disease or response to treatment. Fluorescein and ICG angiography are universally employed throughout the world as standard ocular diagnostic tests.
What Are The Risks Of Eye Angiography?
Both fluorescein angiography and indocyanine green angiography are considered very safe and serious side–effects from these tests are uncommon. However, there is the possibility that a patient may have a reaction to the dyes. While fluorescein contains no iodine and is safe in patients known to be allergic, indocyanine green is currently formulated with iodine and should not be used in these individuals. Some people may experience slight nausea after dye injection that usually passes quickly. Patients who are allergic to the dye can develop itching and a skin rash. These symptoms generally respond quickly to oral medications such as anti–histamines or steroids. Very rarely, a sudden life threatening allergic reaction called anaphylaxis can occur. This condition requires medical treatment. There is also a possibility of an infiltrate of the dye into the skin at the injection site; this would cause some discomfort or discoloring of the skin for several days. Fluorescein dye will also turn a patient’s urine bright yellow to orange and may slightly discolor the skin as well for a brief period. For special patient populations, there may be individual risks of these procedures that your physician will specify for you.
OPTICAL COHERENCE TOMOGRAPHY (OCT)
Optical Coherence Tomography (OCT) is a diagnostic test that allows for the imaging of the neuroretinal layers and measurement of its’ thickness. OCT is very useful in detecting retinal anomalies and pathologies secondary to a variety of conditions. It provides very valuable information and is also useful for following the response to a treatment. OCT testing has become a standard of care for the assessment of most retinal conditions, primarily involving the macula. OCT uses rays of light to measure retinal thickness and can be performed in a few minutes. No radiation or X–rays are used in this test.
Ultrasound is a test that uses sound waves to assess ocular and retinal conditions. If your doctor cannot view the retina because of some opacity that blocks the view, they may use an ultrasound to determine the general status of the retina and to view the density of particular retinal lesions. Ultrasound is commonly used to assess the retina in patients with a dense cataract, severe corneal opacities, or vitreous hemorrhage. Ultrasound is simple to perform, painless, and does not involve any anesthesia or radiation.
This test is designed to find abnormalities in the macula, the reading area of the eye. It helps to find many problems early, when they may still be treatable. Ideally the Amsler grid should be examined daily. It is often easier to remember to look at the grid if it is placed where you are sure to see it, such as on the refrigerator or the bathroom mirror.
The grid consists of a pattern of vertical and horizontal lines with a dot in the center. Test each eye separately, covering the other eye. Glasses should be worn if they are normally needed for reading, hold the grid at approximately 18 inches from your face. You should look only at the central dot and while doing this, notice whether all of the lines are present.
You should also look for any areas where the lines are wavy or distorted. Any areas where the grid is missing, wavy, or distorted, that are significantly different from your baseline should be reported to your eye doctor immediately.
This is a relatively easy, inexpensive tool used to detect changes in one’s central vision. Although new techs are being developed to enhance the early detection of macular problems costs and availability still make the Amsler grid a useful universal tool.