Age-Related Macular Degeneration
Age Related Macular Degeneration is the leading cause of visual impairment in people over 50 years old in the United States. It is important for people at risk, generally people over the age of 60 years, to have an understanding of what exactly comprises macular degeneration.
What is Age Related Macular Degeneration?
Age Related Macular Degeneration is a disease of unknown cause that affects the adult eye, specifically the retina. The retina lies in the back of the eye and contains the cells that function by receiving visual information from the environment. The macula is in the center of the retina and contains the cells responsible for the center of our visual field. The remainder of the retina is used primarily for Peripheral vision. It is the macula that is affected in macular degeneration. This is why patients with macular degeneration exPerience a decrease in their central vision.
The earliest signs of macular degeneration are the appearance of small yellow spots called drusen which appear under the retina in the macula. These drusen can be detected during a complete eye exam, but their presence does not necessarily mean that the patient will have vision problems. They can be found in young patients without macular degeneration. When they are accompanied by a decrease in vision we use the term macular degeneration. There are two forms of macular degeneration: the Dry type and the Wet type.
The Dry type is much more common and it is characterized by the presence of drusen with thinning of the layer beneath the retina. This can lead to progressive decreased vision. Dry macular degeneration can be mild, and patients can maintain useful vision.
The Wet type is much less common but tends to be more aggressive. It is characterized by the growth of abnormal blood vessels underneath the retina. These vessels may bleed or leak causing a more acute vision change. This type of macular degeneration can cause a loss of the center of the vision but rarely causes complete blindness.
Symptoms of Macular Degeneration
The earliest symptom of wet macular degeneration is visual distortion. Patients usually notice that objects look crooked or bent, or that the center of the vision is dark or even missing. An amsler grid is a hand held chart with a grid pattern, which is useful to detect early visual distortion in wet macular degeneration. The earliest symptom of dry macular degeneration is usually difficulty reading.
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Amsler Grid |
Diagnosis
Macular degeneration is diagnosed by a dilated eye examination and occasionally by further testing. Patients suspected of having wet macular degeneration should have a test called fluorescein angiography as soon as possible. This test is performed by injecting a vegetable dye into an arm vein while a photographer takes photographs of the retina. Using this test, the abnormal blood vessels may be identified.
Treatment
Most cases of macular degeneration do not need to be treated, and patients maintain good vision. A small percentage of patients who develop the wet form may benefit from a laser treatment. This can only be determined by an ophthalmologist experienced in the interpretation of fluorescein angiography and the treatment of wet macular degeneration.
There are surgical procedures available for the treatment of wet macular degeneration. One procedure is called submacular surgery where an incision is made in the retina and instruments are used underneath the retina to remove the abnormal blood vessels. Tissue plasminogen activator or TPA can be used to liquefy blood clots so that subretinal blood can be removed from underneath the retina. Results with age related macular degeneration have been limited and the procedure appears to work better for a condition called presumed ocular histoplasmosis which is also associated with abnormal subretinal blood vessels.
Another surgical procedure called retinal translocation is an option in certain cases of macular degeneration. In this procedure, the retina is surgically lifted and rotated away from the abnormal blood vessels and the vessels may then be exposed to laser without harming the center of the macula.
Photodynamc therapy (PDT) received FDA approval. This procedure uses a photosensitizer which is a drug that is injected into an arm vein followed by a laser treatment. The photosensitizer allows the abnormal vessels to be targeted so that the damage to the surrounding retina is limited.
Prevention
There has been much controversy regarding the nutritional treatment of macular degeneration. Some ophthalmologists believe that antioxidant vitamins such as vitamins A and C may slow the progression of macular degeneration. The use of supplemental Zinc has also been advocated. To date there is no convincing evidence that any of these treatments are effective. There is a study in process to determine the usefulness of these treatments.
The earlier wet macular degeneration is detected, the greater the possibility that a laser treatment may be effective in maintaining vision. Therefore, patients are encouraged to use an amsler grid regularly, and see their ophthalmologist should they have any symptoms.
