Age related macular degeneration or ARMD is the most common cause of irreversible
vision loss for people over the age of 60. It is estimated that 2.5 million people
in developed countries will suffer visual loss from this disorder and that there
are approximately 200,000 new cases diagnosed every year.
Macular degeneration is most common in people over the age of 65 but there
have been some cases affecting people as young as their 40s and 50s. Symptoms
include blurry or fuzzy vision, straight lines like telephone poles and sides
of buildings appear wavy and a dark or empty area may appear in the center of
vision.
What is the Macula?
The macula is the small portion of the retina located at the center of this light
sensitive lining at the back of the eye. Light rays from objects that we are looking
at come to a focus on the retina and are converted into electrical impulses that
are then sent to the brain. The macula is responsible for sharp straight-ahead
vision necessary for functions such as reading, driving a car and recognizing
faces.
The effect of this disease can range from mild vision loss to central blindness.
That is, blindness "straight ahead" but with normal peripheral vision from the
non-macular part of the retina which is undamaged by the disease.
Two types of Macular Degeneration
Ninety percent of ARMD is of the "atrophic" or "dry" variety. It is characterized
by a thinning of the macular tissue and the development of small deposits on the
retina called drusen. Dry ARMD develops slowly and usually causes mild visual
loss. The main symptom is often a dimming of vision when reading.
The second form of ARMD is called "exudative" or "wet" because of the abnormal
growth of new blood vessels under the macula where they leak and eventually
create a large blind spot in the central vision. This form of the disease is
of much greater threat to vision than the more common dry type.
What are the causes of ARMD?
Unfortunately, the cause of this eye condition is not fully understood but it
is associated with the aging process. As we age, we become more susceptible to
numerous degenerative processes like arthritis, heart conditions, cancer, cataracts
and macular degeneration. These conditions may be caused by the body's overproduction
of free radicals.
During the metabolic process, oxygen atoms with an extra electron are released.
These extra electrons are quite destructive and cause cellular damage, alter
DNA, and are thought to be at least partially responsible for many of the degenerative
diseases mentioned above. The production of these free radicals is normal during
metabolism but the body produces its own "anti-oxidants" to neutralize them.
Some of the vitamins in the food we eat also have anti-oxidant properties.
These are vitamins A, C, E and beta-carotene. Unfortunately, smoking, poor nutrition
and other lifestyle factors result in the body producing too many free radicals.
For this reason, lifestyle factors may contribute to the risk of ARMD.
There is some evidence to suggest that ARMD has a genetic basis, as the condition
tends to run in families. The exact nature of this familial tendency, however,
has not been clarified. It has been suggested from twin studies that there is
a defect in the genes responsible for the integrity and health of the retina.
Exposure to certain types of light may also play a role. Studies performed
on fishermen in the Chesapeake Bay suggest that long-term exposure to ultraviolet
light from the sun may increase the risk of ARMD and other eye conditions such
as the development of cataracts.
It has also been hypothesized that hyperopia or farsightedness may also play
a role in the development of the disease. It is thought that the shortening
of the eye in hyperopia may cause changes in the membrane below the macula and
in its blood vessels.
In the dry form of the disease, some form of inflammation may also be a factor
although what causes the inflammation is not known.
How is it treated?
Although researchers are spending a great deal of time investigating the cause
and treatment of ARMD, there is no real cure available. The goal of current treatment
efforts is to attempt to stabilize the condition.
For the more severe wet form of the disease, doctors have tried laser photocoagulation.
This treatment, however, is not without dangers and is only beneficial in the
very early stages of the condition, which is why early detection is so important.
This technique involves directing a beam of laser light at the abnormal blood
vessels in order to destroy them and prevent their leaking. Provided that the
blood vessels have not grown under the macula, this treatment can be helpful
in arresting the progress of the disease. If the blood vessels are already under
the macula, the laser may cause scarring and permanent vision loss.
Several new treatments are under development and scientific evaluation.
A new type of treatment called photodynamic shows promise. A drug, injected
into the arm travels to the affected eye and is then exposed to a non-thermal
red light. This light activates the drug to close and seal off the abnormal
blood vessels. The entire treatment only takes about 30 minutes and requires
no anesthetic.
Treatment using proton beams, which release power at predetermined target site
and depth, has also been experimentally tested for treatment of wet-ARMD.
Are Vitamins and Nutrition Useful?
No treatment exists for the dry form but many doctors recommend that a combination
of specific vitamins and minerals helps slow the progression of the disease.
Recently a study has been published in The Archives of Ophthalmology (American
Medical Association)that provides conclusive evidence to support this theory.
Anti-oxidant vitamins may help to neutralize the free radicals that are associated
with this degenerative process. Zinc, one of the most common trace minerals
in our body, is highly concentrated in the retina and surrounding tissues and
is a requirement for chemical reactions in the retina. | 