As part of their retinal evaluation, many patients will undergo fundus photographs and fluorescein angiography. Fundus photographs are color photographs of the retina in which a high-magnification camera is used to photograph the back of the eye, its blood vessels and tissues. These photographs allow the doctor to study the back of the eye and, for patients with a chronic eye problem , document the eye for future reference.
A fluorescein angiogram combines a fluorescent dye with rapid-sequence photography to study the blood flow, vessels and tissues of the retina. After the fluorescein dye is injected into an arm vein, 30 to 60 photos are taken as the dye passes through the blood vessels of the retina, allowing the doctor to identify problem areas of the retina or retinal blood vessels. The entire test takes about 45 minutes.
Fluorescein is a relatively safe dye. As with any injected medicine, there is a small risk of an allergic reaction. However, unlike the dye used for CT scans, heart angiograms and kidney studies, fluorescein dye contains no iodine. Therefore, the risk of allergic reactions or kidney problems from the injection is much lower. Patients who have allergies to iodine dyes can safely receive the fluorescein injection.
After the test, vision may be blurry for several hours due to the multiple bright flashes of light. The dye also gives the skin an orange-brown tinge for several hours after treatment. The dye is eventually passed in the urine, which may appear bright green for the next 24 hours.
Fluorescein angiography uses photography not X-rays, which means there is no exposure to radiation from this test. Because angiograms are so effective at detecting abnormal blood vessels, patients often undergo repeated angiograms on return visits to evaluate the response to treatment and determine the need for additional treatments.
Occasionally, patients undergo a different type of angiography called Indocyanine Green Angiography (ICG). This test is similar to a fluorescein angiogram except that it uses indocyanine green dye. In some cases, ICG may allow identification of an area of leakage not visible on the fluorescein angiogram.
Optical Coherence Tomography (OCT) is a non-contact, noninvasive, advanced imaging technique used to obtain high-resolution cross-sectional images of the retina.
OCT is often used to diagnose selected macular diseases such as macular holes, macular edema, age-related macular degeneration, central serous retinopathy, epiretinal membranes, and retinal inflammatory diseases. OCT utilizes technology that is similar to CAT scans of internal organs, using a scattering of light to rapidly scan the eye to create an accurate cross-section. Unlike other imaging techniques, OCT uses no radiation, sound, or radiofrequency waves. As a result, there is no risk to the patient or harmful side-effects. OCT also measures the thickness of retinal nerve fiber layers to diagnose glaucoma and other diseases of the optic nerve.
B-scan ultrasound is a diagnostic test used to assess various diseases of the eye. It is most useful when direct visualization of intraocular structures is not possible. In such cases, diagnostic B-scan ultrasound can give valuable information on the status of the lens, vitreous, retina, choroid, and sclera.
Ophthalmic ultrasonography uses high-frequency sound waves, which are transmitted from a probe into the eye. As the sound waves strike intraocular structures, they are reflected back to the probe and converted into an electric signal. The signal is subsequently reconstructed as an image on a monitor, which can be used to evaluate the eye and document pathology.