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What is age-related macular degeneration?
Age-related macular degeneration (AMD) is an eye disease that is
present to at least a mild degree in millions of older Americans. It is
a leading cause of visual loss in this country. AMD affects the macula,
a small portion of the retina. The retina is the light-sensing nerve
tissue that lines the inside of the eye. All parts of the retina
contribute to sight, but only the macula can provide the sharp,
straight-ahead vision that is needed for driving and reading small
print. As a person ages, harmful changes may occur in this small but
important area of the retina, causing difficulties in reading and other
tasks that require good central vision. Scientists do not know why these
macular changes occur. But aging evidently plays a major role in the
process. That is why it is known as age-related, or senile, macular
degeneration.
Do people with age-related macular degeneration usually go blind?
No. Although AMD is a leading cause of visual loss, it is important to
know that the majority of people with AMD continue to have almost normal
vision throughout their lives. Even those who are severely affected do
not lose all their sight, but retain enough to move about independently
and make use of helpful devices called low vision aids. And for a
limited number of people who develop a rapidly worsening form of AMD
that seriously endangers vision, there is a sight-saving treatment
developed through research.
Who gets age-related macular degeneration?
Usually, AMD does not develop until a person is 65 or older. But a few
people are affected by the disease while still in their forties or
fifties. A person's chances of developing AMD are greater than average
if he or she has a near relative with the disease. Scientists are now
trying to learn what other factors might place a person at risk for AMD.
What are the signs and symptoms of age related macular degeneration?
Most people with AMD have a form of the disease that develops very
slowly. It is called the "dry" form. In it, tiny yellowish deposits
called drusen develop beneath the macula. Also, the layer of
light-sensitive cells in the macula becomes thinner as some cells break
down. These changes typically cause a dimming or distortion of vision
that people find most noticeable when they try to read.
Generally, if one eye has dry AMD, the other eye will also have some
signs of the condition. Thus the person with dry AMD may eventually have
visual problems in both eyes. However, the dry form of AMD rarely causes
total loss of reading vision.
A much greater threat of visual loss arises when the dry form of AMD
gives way to the "wet" or neovascular form of the disease. This
condition arises in a small percentage of AMD patients. In it, new blood
vessels grow beneath the macula. These abnormal vessels leak fluid and
blood, causing the light sensitive cells near them to sicken and die.
This process generally produces marked disturbance of vision in the
affected eye: Straight lines look wavy, and later there may be blank
spots in the field of vision.
If the leakage and bleeding from new vessels continues, much of the
nerve tissue in the macula may be killed or injured within a period of a
few weeks or months. Such damage cannot be repaired, because the nerve
cells of the macula do not grow back once they have been destroyed.
Although only a small percentage of people with AMD develop the
neovascular form, they make up the vast majority of those who experience
serious visual loss from AMD.
What treatment is available for people who have new blood vessels from
AMD?
A few years ago, a clinical study found that there is a treatment that can help most
people whose sight is threatened by the wet or neovascular form of AMD.
This treatment is called laser photocoagulation. In it, powerful light
rays from a laser are directed into the eye and focused at a tiny spot
on the macula. The aim of the laser treatment is to preserve vision by
destroying abnormal blood vessels.
In this study, laser treatment reduced the risk of severe
vision loss by more than half in people with neovascular AMD. However,
this treatment is best applied soon after the new blood vessels develop,
before they have reached and damaged the fovea-the central part of the
macula.
Can everyone with AMD benefit from laser treatment?
No. Laser photocoagulation is of value only to the relatively few
people who have the neovascular form of AMD, with new blood vessels
actively growing in the macula and threatening to cause serious vision
loss. There is no evidence that laser treatment is of any value for
people with the dry form of AMD. Also, because the laser cannot restore
vision already lost from AMD, an eye whose macula has been badly damaged
by this disease would not benefit from laser treatment. That is why it
is so important for AMD-and neovascular AMD in particular-to be detected
early.
How does a person know whether AMD is present, and whether treatment is needed?
Drusen and the other macular changes typical of dry AMD cannot be
seen by the person who has them, but are visible to an eye care
specialist examining the eye. Anyone who is middle-aged or older should
visit an eye care specialist regularly to be checked for early signs of
AMD, glaucoma, and other eye diseases that are linked to aging.
Generally, when dry AMD is found, the patient is encouraged to return
for further check-ups. Also, he or she may be taught to perform a
simple, at-home test for visual changes. The test involves looking at a
piece of paper marked with a grid of straight lines. If some of the
lines begin to look curved or are not visible at all, this may be a
valuable warning that new blood vessels are developing and laser
treatment should be considered. Patients who use the grid are asked to
look at it regularly and tell the doctor right away if they notice any
changes in its appearance. If it is suspected that neovascular AMD is
developing, a procedure called fluorescein angiography is generally
performed. In this procedure, a dye called fluorescein is injected into
the arm. Photographs are taken to show the movement of the dye as it
reaches the eye and passes through the blood vessels of the retina. If
there are new vessels leaking fluid or blood in the macula, the
photographs will show their exact location, and serve as a guide for
treatment.
How is laser treatment performed?
Laser treatment is performed by a specially trained ophthalmologist
in his office or in an eye clinic at a medical center. A local
anesthetic may be used to prevent discomfort during the laser treatment
session. The session generally takes only a few minutes. Soon
afterwards, the patient is able to return home and continue his or her
normal activities.
The patient usually will be asked to return to the doctor's office for
follow-up appointments. If additional growth of new blood vessels is
found, further laser treatment may be indicated. Between follow-up
visits, the patient can use the home test described above to detect any
visual changes that might signal renewed blood vessel growth.
Is there any way to prevent AMD?
At present, there is no proven method of preventing dry AMD or the
onset of the neovascular form of the disease. Discovering effective
means of prevention is a major goal of the National Eye Institute, the
United States Government agency that conducts and supports research on
the eye and visual disorders. NEI-supported scientists are now seeking
the underlying causes of AMD, in hopes of finding some way to halt the
disease in its early stages or eventually prevent it altogether.
Research on the treatment of neovascular AMD is
continuing. A relatively new device called the krypton laser is being
tested in people with neovascular AMD, especially those who have new
blood vessels very close to the center of the macula.
What help is available to the person who has already lost vision from AMD?
There are many useful devices that can help a partially sighted person
to make the most of his or her remaining vision. Called low vision aids,
these devices have special lenses or electronic systems that produce
enlarged images of nearby objects.
If you need low vision aids, your eye care specialist can generally
prescribe them. Often, he or she will be able to suggest further sources
you might contact to get information about counseling, training and
other special services for people with low vision. Through such sources
as a nearby school of medicine or optometry, or a local volunteer group
devoted to helping the visually handicapped, you can learn a great deal
about low vision programs in your area. It may help you to know that
many organizations "for the blind" also serve people with low vision.