Common tests for retina conditions

Diagnostic B-scan
A B-scan is an ultrasound machine used to view the internal structures of the eye.  With the B-scan, the operator can see a cross-section of the eye.  It is used when, during a dilated exam, the physician cannot obtain a clear view of the patient’s retina or other internal structures due to bleeding, a dense cataract, corneal cloudiness or lesions.  It can also be used to locate and follow cancerous tumors and other abnormalities.

In order to perform a B-scan, an anesthetic drop is applied to the surface of the eye.  While the patient is reclined in an exam chair, a technician places a probe on the surface of the eye and moves it to view the rear of the eye.  Photographs may be taken using the probe.

Diagnostic A-Scan
Similar to the B-scan machine, a diagnostic A-scan is an ultrasound machine.  While the B-scan provides a view of the cross-section of the eye, the A-scan provides a view of the top section.  The diagnostic A-scan allows the technician to calculate the size of a lesion within the eye.

Fluorescein angiography
Fluorescein angiography is a common test used to diagnose and monitor the impact of diabetic retinopathy and macular degeneration.  Fluorescein angiography is a diagnostic procedure that uses a special camera to take a series of photographs of the retina, the light sensitive tissue in the back of the eye.  The photographs are transmitted to a computer, allowing your doctor to view a series of digital retinal images.

To prepare for a fluorescein angiography test, you will receive dilating drops to expand the size of your pupils, allowing for an easier view of the back of your eye.  A nurse will then inject a vegetable-based dye (fluorescein) in your arm. The dye travels through the veins and into the arteries that circulate throughout the body.  As the dye passes through the blood vessels of the retina, a technician uses a special camera to take approximately two dozen photographs of the retina.

The main purpose of this test is to reveal the condition of the blood vessels within the retina.  If the blood vessels in the retina are abnormal, the photographs will show dye leaking into the retina or staining the blood vessels. Damage to the lining underneath the retina or the appearance of abnormal new blood vessels growing beneath the retina may also be revealed. The precise location of these abnormalities can be determined by a careful interpretation of the fluorescein angiogram by your ophthalmologist.  The ophthalmologist uses this information to determine whether additional monitoring, laser procedures or injections are warranted.

There are some risks associated with fluorescein angiography, but the diagnostic benefits of the tests overwhelmingly outweigh these risks.  After the dye is injected, your skin may turn yellowish for several hours. This color disappears as the dye is filtered out of the body by the kidneys. Because the dye is removed by the kidneys, your urine will turn bright yellow for up to 48 hours following the test.

Some individuals may experience slight nausea during the procedure, but this usually passes within a few seconds. If the dye leaks out of a fragile vein during the injection, some localized burning and yellow staining of the skin may occur. This burning usually lasts only a few minutes and the staining will go away in a few days.

Allergic reactions to fluorescein dye are rare. If they occur, they may cause a skin rash and itching. This is usually treated with oral or injectable antihistamines, depending on the severity of the symptoms. Even more rarely, severe allergic reactions (anaphylaxis) can occur and be life threatening.

Fundus photos
Fundus photos are photographs taken through a dilated pupil of the patient’s retina using a computer and an attached 35 mm camera.  Fundus photography is most commonly used to document the appearance of the retina, blood vessels and optic nerve over time.  By comparing new and old photos, your eye doctor can assess the speed at which a disease is progressing.  Fundus photography is most commonly used to follow macular degeneration, diabetes and glaucoma.

Nerve fiber layer analyzer
A nerve fiber layer analyzer is a computerized camera that provides a graphic and statistical view of a patient’s optic nerve.  It is often simply called an OCT, which stands for optical coherence tomography.  In addition to its use for diagnosing glaucoma, the nerve fiber layer analyzer can also provide clear interpretations of macular holes and macular edema (swelling).

The test procedure is quite brief and painless.  After receiving eye drops to dilate the pupil, the patient sits in front of the camera, and the camera scans the eye for approximately five minutes each.  The patient will focus on a fixation light within the camera and the technician will provide any additional directives.

Visual field test
The visual field is the entire area that a person can see when the eye is focused on a central point.  It includes central and peripheral (side) vision.  While the visual field test is used primarily to monitor glaucoma, testing central vision is particularly important for patients at risk for macular degeneration.  In addition, macular and optic nerve head edema (swelling) can be monitored with this test.

Patients often find it difficult to detect changes in their visual field since one eye may compensate for visual field loss in the other eye.  This compensation is one reason why visual field tests are performed separately on each eye.

Most visual field tests incorporate computerized machines that require the patient to stare at a fixed point in the middle of a large domed area.  A computer program will flash small lights in different locations on the surface of the domed area.  While staring straight ahead, the patient is asked to press a button when he or she sees the small lights in his peripheral vision.  The computer summarizes the patient’s responses and prints a graphic interpretation of the patient’s visual field.  While just one visual field test can be extremely helpful in identifying visual field loss, a series of tests over a period of years allows your doctor to assess whether visual field loss is stable or progressing.  Visual field tests will take between 20 and 45 minutes depending on the level of test ordered by the doctor.