By
Jonathan Yoken, MD
MACULAR
DEGENERATION
What is
the macula?
The macula is a specific area of the retina. It is at the center
of the visual field-when looking directly at an object, you are
seeing it with the macula, while the rest of the retina provides
peripheral vision. Although it represents only a small fraction
of the total size of the retina-about the size of the capital
letter "O" on this page-the macula is crucial for visually
demanding tasks like reading, driving a car, and color vision.
Diseases of the macula may interfere with "detail vision",
making these activities more difficult. Macular problems can also
cause images to appear distorted, or may cause an area of cloudiness
or darkness to form at the center of the visual field. Fortunately,
many diseases that affect the tiny macula may spare the rest of
the retina, thereby preserving peripheral vision. Therefore, diseases
such as Age Related Macular Degeneration (ARMD) rarely result
in complete loss of sight.
What is
degeneration of the macula?
In some individuals,
tiny dot-like deposits (known as drusen) slowly accumulate beneath
the macula. While these deposits usually do not cause visual loss
directly, they indicate that the patient is at risk for developing
further problems with the macula. Usually, these deposits would
not be apparent before the age of 50.
Visual problems
in macular degeneration take two basic forms. The first, milder
problem occurs as the cells of the macula slowly lose sensitivity
and may become less numerous. This may result in fluctuating vision-the
sight is clearer on some days than others-and slowly (typically
over months to years) vision may worsen. This is referred to as
the "dry" form of macular degeneration.
The second
type of problem occurs more suddenly and may cause a more serious
drop in vision. Tiny clusters of abnormal blood vessels may begin
to grow beneath the macula. These vessels "leak" and
blood or watery fluid may accumulate beneath the macula. This
can result in irreversible damage to the macula, resulting in
loss of the central detail vision. The presence of leaks is often
referred to as the "wet" form of macular degeneration.
If these vessels
can be identified at an early stage, it may be possible to seal
them with laser treatment. In many cases, however, laser cannot
be used because the vessels have already spread too far, or the
exact location of the leak cannot be found.
Why does macular degeneration occur?
What can be done to prevent macular degeneration?
While the
most important risk factor for macular degeneration is age, it
is not yet understood why macular degeneration occurs in some
seniors and not in others.
There may
be some inherited factor which predisposes individuals to have
this condition, and research to identify the genes which are associated
with macular degeneration is ongoing. The development of drusen,
and the slow loss of retina cells that sometimes occurs, is not
preventable by any means yet identified. However if the genetic
basis of macular degeneration was identified, it might be possible
to correct the defect before macular degeneration can begin. Many
researchers are working on this question, but it remains a difficult
problem.
If a person
has macular degeneration, it appears that keeping the entire body
healthy-control of blood pressure, control of cholesterol, good
nutrition, and avoiding cigarettes-helps to reduce the risk of
developing visual loss. The Age-Related Eye Disease Study (AREDS)
was a major study sponsored by the National Eye Institute (NEI).
In the study, scientists looked at the effects of zinc and antioxidants
(vitamin C, vitamin E & beta carotene i.e. provitamin-A),
on patients with cataracts and age-related macular degeneration
(AMD). Patients with intermediate to advanced AMD, as determined
by the doctor, who were taking the anti-oxidant and zinc combination
had a demonstrable decrease in the incidence of developing wet
AMD
While most
patients in the study experienced no serious side effects from
the doses of zinc and antioxidants used, a few taking zinc alone
had urinary tract problems that required hospitalization. Some
patients taking large doses of antioxidants experienced some yellowing
of the skin. The long-term effects of taking large doses of these
supplements are still unknown. Previous studies have shown that
individuals who smoke and take beta-carotene are at an even greater
risk of developing lung cancer, and therefore current and recent
smokers should not take beta-carotene.
If you have
intermediate (or advanced macular degeneration in one eye only),
talk to your physician about taking nutritional supplements. Your
doctor can help you determine if they may be beneficial-and safe-for
you, and what types and doses of supplements to take. The doses
used in the study were: Vitamin C 500 mg, Vitamin E 400 IU, Beta-carotene
15 mg, Zinc 80 mg, as zinc oxide, Copper 2 mg, as cupric oxide
(copper should be taken with zinc, because high-dose zinc is associated
with copper deficiency).
An addition
factor that may aggravate macular degeneration is unprotected
exposure to the sun's UV rays. While this is not yet proven, in
our practice most patients find that sunglasses (with UV protection)
are more comfortable in the Florida sun.
How is macular degeneration treated?
There is no
treatment for dry AMD, except for vitamin supplementation as described
above if recommended by your doctor. There are some treatments
for wet AMD, but whether or not you are a candidate for treatment
depends on the type and location of the leak. Most of these treatments
are best at stabilizing the vision or slowing the progression
of vision loss, rather than restoring vision.
What should
I watch for?
Your doctor
will schedule regular follow-up appointments to monitor your condition.
In addition, we strongly recommend monitoring your vision with
an Amsler grid at least twice a week, so that any changes in vision
will be recognized as early as possible. Instructions on how to
use the grid will be provided.
Any changes on the Amsler grid-waviness of the lines, blank
or missing lines, or blurring of the lines-should be reported
to your doctor immediately. Early detection is our best defense
against visual loss in macular degeneration!
Amsler Grid
