Progression of Macular Degeneration
Macular
degeneration, in most cases is a slowly progressive disease. It gradually
causes a loss of the photoreceptor cells of the central retina leading
to worsening of vision. If the damage is limited to the loss of cells,
then the patient is said to have "dry" macular degeneration.
Sometimes abnormal vessels begin to grow underneath the macula, in the
area of degeneration. This is a process called choroidal neovascularization,
and the blood vessels themselves are referred to as a choroidal neovascular
membrane (CNVM). It appears there are at least two reasons why these
vessels grow into the degenerated areas. The healthy retinal cells,
which would normally prevent abnormal blood vessel growth, are no longer
present. And, blood vessel growth is stimulated by the presence of certain
protein factors that encourage these blood vessels to grow. These chemical
substances are known as angiogenic growth factors. If abnormal blood
vessels are present, they may leak fluid or blood underneath the retina.
This condition is known as "wet" macular degeneration. Wet
macular degeneration is potentially worse than dry age-related macular
degeneration because the blood vessels may continue to grow, destroying
a far larger area of the central retina than that caused by dry degeneration
alone. The underlying tissue complex of blood vessels and fibrous support
tissue may form a large scar under the retina. In wet degeneration,
the retina may swell, which then causes the distortion of lines seen
on the Amsler grid. "Dry" and "wet" macular degeneration
are not two separate diseases. The "wet" form is simply a
complication or more advanced form of the disease. Anyone with "dry"
macular degeneration must be examined periodically to be sure they are
not progressing to the "wet" form.
Nutrition (Prevention)
A major national trial called the Age Related Eye Disorder Study (AREDS) sponsored by the National Institutes of Health and National Eye Institute, looked at several thousand people with macular degeneration. Patients in the trial took either certain vitamins or a placebo (sugar pill), and neither the patients nor the doctors knew what they were taking. At the end of the study period, the patients who took the high dose vitamins did far better than the patients who took the placebo. The tested nutritional factors were Beta-carotene, Vitamin C, Vitamin E, and Zinc. However, you should discuss the appropriate formula for vitamin therapy with your ophthalmologist. The therapeutic dosage for these supplements is very high. There are potential side effects, and not everyone will benefit from this regimen. The study continues, and other supplements (lutein, zeaxanthine) are under investigation as well. Another nutrition supplement, Omega 3 fatty acids, has been strongly associated with lower levels of macular degeneration. Omega 3's are found in oily fish, fish oil capsules and flax seed oil. Some nutritional supplements are popular in alternative medicine such as bilberry, which is a powerful antioxidant. But there are no good, scientific studies looking at the effectiveness of these other supplements.
Treatment
Dry Macular Degeneration
There is currently no guaranteed treatment for "dry" macular
degeneration, but some interventions have been shown to be helpful.
Treatment strategies have been directed at several areas and much research
is currently taking place.
Wet Macular Degeneration
Thermal Laser: The presence of abnormal blood vessel
growth is the most devastating complication of macular degeneration.
A great deal of work has been directed at treating this problem. Thermal
laser ("hot" laser) treatment has been successfully used to burn out
abnormally growing blood vessels and prevent deterioration of vision
due to "wet" age-related macular degeneration. The laser is done in
an office setting and takes only a few minutes. The laser beam is microscopic
and there is no pain involved in this treatment. Unfortunately, only
a few patients meet the very strict criteria for successful laser treatment:
i.e. the abnormal blood vessels must be easily seen on photographic
testing, and they must not be directly in the center of the macula.
Treating the center of the macula with laser burns the visual cells
and causes a permanent blind spot and loss of vision. Therefore, only
blood vessels away from the exact center of the retina may be treated.
Central Wet Macular Degeneration
Photodynamic Therapy (PDT): Photodynamic therapy or PDT works
in some situations where thermal laser cannot be used. The theory behind
the treatment is to use such a low dose of laser, that it will not be
harmful to the central retinal cells and therefore preserve vision.
The laser dose used is too weak to be helpful under normal circumstances,
but just prior to treatment, a special dye (Visudyne®)
is injected into the blood stream. Visudyne® absorbs
the laser energy, undergoes a chemical reaction and causes the blood
vessels to coagulate. The dye enhances the laser effect only on these
abnormal blood vessels, destroying them while at the same time preserving
the delicate retinal visual cells. Several trials have shown that Visudyne®
works in many cases to prevent further deterioration of vision, but
only a few patients improve their vision. Recent studies have suggested
that the additional injection of a steroid (cortisone-like drug), Kenalog®,
can augment the effect of PDT and may improve vision. The effectiveness
of steroids remains uncertain at this time.
New Medical Treatment: By far the most exciting and promising modalities for treatment of wet macular degeneration are the new biologic therapies. There are new steroid-like drugs that are now being tested in ongoing trials. These steroids are designed to be more effective and have fewer side effects than current steroids. Drugs currently in testing include Retanne® and Posurdex®.
Another class of drugs works by blocking the vascular growth factors that stimulate the blood vessel growth seen in wet macular degeneration. Sometimes called anti-VEGF drugs, they offer promise of a significant improvement in the treatment of abnormal blood vessels. One such drug Macugen®, has been shown in clinical trials to be effective in slowing or stopping macular degeneration, and it was approved for use by the FDA in wet macular degeneration in 2005. Macugen® seems to have some effect in improving vision as well as stablizing vision. It must be administered as an injection into he eye itself every 6 weeks. Another drug, Lucentis®, is in the late stages of a Phase 3 trial, and shows great promise, but it is not yet available to the public. Lucentis® also must be administered via intra-ocular injection, in this case once a month.
Low Vision
Macular degeneration is a very frustrating disease. Although it is often not possible to prevent some vision loss in age-related macular degeneration, one can still have a productive life. Low vision aids are available to enable people with macular degeneration to better utilize their remaining vision. These aids and devices are varied and may involve the use of magnifying lenses or glasses, small telescopes, large print books and large print appliances, closed circuit TV enlargers, etc. If your vision is poor due to macular degeneration, you may want to consider a referral to a low vision specialist. This is a doctor who can work with you to help you get the most out of your remaining sight.
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