Macular
degeneration is a leading cause of blindness.
Age-related macular degeneration is a chronic eye
disease that occurs when tissue in the macula, the
part of your retina that's responsible for central
vision, deteriorates. The retina is the layer of
tissue on the inside back wall of your eyeball.
Degeneration of the macula results in blurred
central vision or a blind spot in the center of your
visual field.
The first sign of macular degeneration may be a
need for more light when you do close-up work. Fine
newsprint may become harder to read and street signs
more difficult to recognize. Eventually you may
notice that when you're looking at an object, what
should be a smooth, straight line appears distorted
or crooked. Gray or blank spots may mask the center
of your visual field. The condition may progress
rapidly, leading to severe vision loss in one or
both eyes.
Macular degeneration affects your central vision,
but not your peripheral vision; thus it doesn't
cause total blindness. Still, the loss of clear
central vision - critical for reading, driving,
recognizing people's faces and doing detail work -
greatly affects your quality of life. In most cases
the damage caused by macular degeneration can't be
reversed, but early detection may help reduce the
extent of vision loss.
The condition tends to develop as you get older,
hence the "age-related" part of its name. Macular
degeneration is the leading cause of severe vision
loss in people age 50 and older.
Signs and symptoms
Macular degeneration usually develops gradually and painlessly. The
signs and symptoms of the disease may vary, depending on which of the
two types of macular degeneration you have.
With dry macular degeneration you may notice the following symptoms:
-
The need for
increasingly bright illumination when reading or doing close work
-
Printed words that
appear increasingly blurry
-
Colors that seem
washed out and dull
-
Gradual increase
in the haziness of your overall vision
-
Blind spot in the
center of your visual field combined with a profound drop in your
central vision
With wet macular degeneration, the following symptoms may appear
rapidly:
In either form of macular degeneration, your vision may falter in one
eye while the other remains fine for years. You may not notice any or
much change because your good eye compensates for the weak one. Your
vision and lifestyle begin to be dramatically affected when this
condition develops in both eyes.
Causes
The macula is the center of your retina and is made up of densely packed
light-sensitive cells called cones and rods. These cells, particularly
the cones, are essential for central vision. The choroid is an
underlying layer of blood vessels that nourishes the cones and rods of
the retina. A layer of tissue forming the outermost surface of the
retina is called the retinal pigment epithelium (RPE). The RPE is a
critical passageway for nutrients from the choroid to the retina and
helps remove waste products from the retina to the choroid.
As you age, the RPE may deteriorate and become thin (a process known as
atrophy), which sets off a chain of events. The nutritional and
waste-removing cycles between the retina and the choroid are
interrupted. Waste deposits begin to form. Lacking nutrients, the
light-sensitive cells of the macula become damaged. The damaged cells
can no longer send normal signals through the optic nerve to your brain,
and your vision becomes blurred. This is often the first symptom of
macular degeneration.
Macular degeneration occurs in two types:
-
Dry macular
degeneration.
Most people with macular degeneration have the dry
form. In fact, macular degeneration always starts out as the dry
form. The dry form may initially affect only one eye but, in most
cases, both eyes eventually become involved. Dry macular
degeneration occurs when the RPE cells begin to thin. The normally
uniform reddish color of the macula takes on a mottled appearance.
Drusen, which look like yellow dots, appear under the retina.
-
Dry macular
degeneration is the result of a deterioration of the RPE brought on
by aging. The light-sensitive cells of the macula continuously shed
used-up outer segments as waste. This waste is broken down and
disposed of by the RPE into the choroid. At the same time, cones and
rods continuously produce new outer segments to replace the
discarded ones.
-
When you develop
dry macular degeneration, the waste disposal system falls apart.
Aging slows the process to a point where waste starts to accumulate
in the RPE. This accumulation interferes with the normal function of
the RPE, causing the light-sensitive cells of the macula to
degenerate.
-
Initially, in
spite of these developments, you may notice little or no change in
your vision. Many people who've received a diagnosis of early-stage
dry macular degeneration may not be bothered with symptoms such as
blurred eyesight unless they live to a very old age. But as the
drusen and mottled pigmentation continue to develop, your vision may
deteriorate sooner. Thinning of the RPE may progress to a point
where this protective layer of the retina disappears. This affects
the overlying cones and rods and may result in complete loss of your
central vision.
-
Wet macular
degeneration.
The wet form accounts for 10 percent to 15 percent of all cases, but
it's responsible for nearly 90 percent of the severe vision loss
that people with macular degeneration experience. If you develop wet
macular degeneration in one eye, your odds of getting it in the
other eye increase greatly.
-
Wet macular
degeneration develops when new blood vessels grow from the choroid
underneath the macula. These vessels leak fluid or blood — hence it
is called wet macular degeneration — and cause your central vision
to blur. All eyes with the wet form also show signs of the dry form,
that is, drusen and mottled pigmentation of the retina. In addition,
what should be straight lines in your sight become wavy or crooked,
and blank spots appear in your field of vision.
-
Much like the dry
form of macular degeneration, a breakdown in the waste removal
system may be what's causing the abnormal growth of blood vessels.
When the waste from the cones and rods isn't disposed of and begins
to accumulate, sufficient flow of nutrients to the macula is
interrupted. The abnormal growth of blood vessels may be a response
to this interruption in the flow of nutrients. And without enough
nutrients, healthy tissue in the macula begins to deteriorate.
-
Sight loss is
usually rapid and severe, resulting in legal blindness, defined as
20/200 vision or worse. This means that what someone with normal
vision can see from 200 feet, a person with 20/200 vision can see
only from 20 feet.
A
comparatively rare form of wet macular degeneration is called retinal
pigment epithelial detachment (PED). In this instance, fluid leaks from
the choroid although no abnormal blood vessels have started to grow
there. The fluid collects under the retinal pigment epithelium, causing
what looks like a blister or a bump under the macula. This kind of
macular degeneration causes the same symptoms as wet macular
degeneration and frequently progresses to wet macular degeneration with
newly growing abnormal blood vessels.
Risk factors
Researchers don't know the exact causes of macular degeneration, but
they have identified some contributing factors. The factors include:
-
Age.
Macular degeneration is the leading cause of
severe vision loss in people age 50 and older.
-
Family history
of macular degeneration.
This increases your risk of macular degeneration.
-
Race.
Macular degeneration is less common in blacks, Asian- and
Indians than it is in other groups.
-
Sex.
Women are more likely than men are to develop macular degeneration
and, because they tend to live longer, to suffer the effects of
severe vision loss from the disease.
-
Light-colored
eyes.
People with light-colored eyes appear to be at greater risk than
those with darker eyes.
-
Exposure to
ultraviolet light.
Long-term exposure to ultraviolet light and blue light (the
wavelength just above ultraviolet), which includes sunlamps as well
as regular sunlight, increases your risk.
-
Low levels of
nutrients.
This includes low blood levels of minerals and antioxidant vitamins,
such as A, C and E. Antioxidants can protect your cells from oxygen
damage (oxidation), which may be responsible for the effects of
aging and for the development of certain diseases such as macular
degeneration.
-
Cigarette
smoking.
Exposure to environmental pollution — especially cigarette smoke —
greatly increases your risk. Smokers are two to three times more
likely to develop macular degeneration than are nonsmokers.
-
Cardiovascular
diseases.
These include circulatory problems, stroke, heart attack and chest
pain (angina).
heart
attack
Stroke
When to seek medical advice
Regular screening examinations can detect early signs of macular
degeneration before the disease leads to vision loss.
But if you notice any changes to your central vision or your ability to
see colors and fine detail, particularly if you're older than 50, see
your eye doctor. Macular degeneration can progress quickly and the
sooner you're diagnosed and treated, the better your chances of limiting
vision loss.
One way to monitor your eyes to determine if you may need to visit your
eye doctor is to check your vision regularly using an Amsler grid. This
simple test may help you detect changes in your sight that you otherwise
may not notice. You can perform the test with the grid in hand, or hang
the grid someplace where you'll see it often — on your refrigerator or
bathroom mirror, for instance.
Here's what you do:
-
Hold the grid 14
inches in front of you in good light. Use your reading glasses if
you normally wear them.
-
Cover one eye.
-
Look directly at
the center dot with your uncovered eye.
-
While looking at
this dot, see whether all of the lines of the grid are straight, are
complete and have the same contrast.
-
Repeat the above
steps with your other eye.
-
If any part of the
grid is missing or looks wavy, blurred or dark, contact your eye
doctor immediately.
Stroke
Macular degeneration
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