EYE DISORDERS
MACULAR DEGENERATION
Macular degeneration is the leading cause of irreversible
severe visual loss in caucasians age 50 or older in the United States.
It has been estimated that this 2.2% of those older than age 65 have
worse than 20/200 vision (legally blind) due to this condition. This
page discusses the condition known as age-related macular degeneration,
or AMD. Topics include:
Note: There are other similar conditions such as ocular histoplamosis,
myopic macular degeneration, and macular degeneration related to angioid
streaks and trauma which will not be separately discussed.
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The retina is thin lining of nerve cells which lines the inside
of the eye. It receives and processes images, and sends these
images to the brain via the optic nerve. The macula is a small,
but very important part of the retina capable of perceiving
the sharpest of images. It is here that our central vision (what
we look directly at), our reading vision, and our color vision
are received. Without the macula, we would be legally blind,
with only peripheral vision (side vision) to guide us. |
| An enlarged view of the macula is shown here. The optic nerve
is the yellow circle with blood vessels leaving it. The nerve
head is about 1.5 mm in diameter. The vessels are retinal arteries
and veins which supply the inner layers of the retina. The center
of the macula is the small red and yellow dot, called the "fovea".
This is our point of visual fixation (with what we look directly
at). |
 |
The condition known as "age-related macular degeneration"
leads to deterioration of the macula, and possible loss of vision. Risk
factors for this condition include:
- Advancing age, over 50 years of age, and especially over 65
- Caucasian race
- A history of visual loss related to macular degeneration in the
other eye
- Certain types of retinal deposits, called drusen
- A family history of macular degeneration
- Tobacco smoking (especially for the more severe
form of macular degeneration)
- Arteriosclerosis and increased cholesterol, possibly hypertension
- A diet deficient in anti-oxidant vitamins and minerals
- A recent study showed that sensitivity to glare
and poor tanning ability were markers of increased macular degeneration
risk. Interestingly, the study could not demonstrate that sun exposure
itself was a risk factor.
Age-related macular degeneration is broadly grouped into two categories:
a "dry" form, and a "wet" form. The next section
discusses these differences.
This form of macular degeneration consists of a slow deterioration
of the retina. Deposits form under the retina called "drusen".
Drusen may block nutrition from reaching the retina from a highly vascular
layer
under the retina called the "choroid". The choroid nourishes
the outer layers of the retina, while the retinal blood circulation
supplies the inner layers. Over time, the retina atrophies, or degenerates,
over these area of drusen, and a spotty loss of vision occurs. If more
and more of these atrophic areas form and merge together, the macula
can take on a moth-eaten appearance, with progressive loss of vision.
This usually occurs over a period of many years.
There is no known treatment for this form of macular degeneration.
Theoretically, it may help to reduce any risk factors one may have (listed
above), but it has not been proven that this will help prevent visual
loss. If a person with macular degeneration has a well balanced diet,
nutritional supplements may not be necessary. If not, a multi-vitamin
is usually recommented (see the section on nutrition below).
This is a more severe and rapidly progressive form of macular degeneration.
In some cases, the "dry" form of macular degeneration will
lead to the "wet" form, but in other cases this form occurs
without warning. Between the vascular choroid layer under the retina
and the retina itself is a dividing membrane called the "retinal
pigment epithelium". If a break occurs in the retinal pigment epithelium,
it becomes possible that an abnormal blood vessel could grow from the
choroid to directly underneath the retina in the macula. Such a break
could occur in an area of drusen, especially drusen that have pigmentation
and appear diffuse or fuzzy. When a new blood vessel grows under the
retina, it is termed "subretinal neovascularization".
Subretinal neovascularization in the macula can be a surgical emergency.
If such a blood vessel is treatable, it should be treated as soon as
possible after the diagnosis is made. Symptoms of this condition, otherwise
known as "wet" macular degeneration, include:
- A change in vision, usually a sudden blurring in one eye.
- Distortion of vision, where straight lines appear crooked in the
affected eye.
- A blind spot appearing in the vision of the affected eye, where
things seem to disappear when looked at. Sometimes, a blind spot will
occur near to what is being looked at instead.
- A change in the size appearance of things, with objects appearing
to be smaller or larger than with the other eye.
Note: other conditions such as ocular histoplasmosis, myopic macular
degeneration, and macular degeneration related to angioid streaks and
trauma can lead to subretinal neovascularization.
Photographic
Simulations of the visual experience with macular degeneration can
be found here.
When an ophthalmologist examines the retina, the blood vessel growing
under the retina can often be seen. Other times, there may be hemorrhage
in or under the retina, obscuring the view of the vessel. Swelling of
the retina can often be observed as well. An additional test, called
a fluorescein angiogram, is usually done as immediately as possible
to better determine where the new, abnormal blood vessel is and if it
can be treated. A fluorescein angiogram is a test done in the office
where a pigmented dye is photographed as it passes through the retinal
blood vessels. For this test, the eyes are dilated, and initial color
photographs are taken of the retina by the photographer. Then, the fluoresein
dye is injected into an arm vein by a physician. This is similar to
having blood drawn. Once the dye is in, the needle is removed, and the
photographs are taken. The dye reaches the eye in a matter of seconds.
About 30 photographs are taken between the two eyes over a 10 minute
time span. The film is then developed, and the ophthalmologist studies
the results. Important information about the leakage and blockage of
blood vessels can be gained from this test.
The diagnosis of macular degeneration depends on several factors:
- A careful history taken by the examiner as to possible risk factors
and symptoms of macular degeneration
- A careful retinal examination to look for evidence of macular degeneration,
or for any precursors of it (drusen)
- Additional tests such as fluorescein angiography and Amsler grid
testing (discussed below)
- Scheduling appropriate follow-up visits, and self-monitoring of
vision by the patient
The "Amsler grid" is a small graph-like chart with a central
dot. It is useful for testing for distortion of vision. To do the test,
the grid is held at normal reading distance (16 inches) with glasses
on if needed. With one eye covered, the central dot is looked at. Any
missing lines, distorted lines, or other abnormality on the chart is
then noted by the patient. The other eye is then tested. This is a way
for patients with risk factors for macular degeneration, or with previously
treated macular degeneration to monitor their vision for development
of "wet" macular degeneration (subretinal neovascularization).
A
Printable Amsler Grid is available here.
Treatment of "dry" macular degeneration
- Unfortunately, there is no cure for this form of the disease
- Vision should be monitored with the Amsler grid for early detection
of the "wet" form of macular degeneration
- Follow-up appointments should be kept as directed
- Nutritional supplements can be considered
Treatment of "wet" macular degeneration
- Once diagnosed with "wet" macular degeneration, it is
implied that subretinal neovascularization is present. If this finding
meets certain criteria on the fluorescein angiogram, laser treatment
may be able to eliminate the abnormal blood vessel.
- If treated with laser, a blind spot will result in the vision.
- The purpose of the laser treatment is to prevent severe loss of
vision. Sometimes some loss of vision may occur with the laser treatment
in order to prevent further loss of vision.
- After sucessful laser treatment, the situation needs to be closely
monitored for signs of recurrence. This includes follow-up examinations
and possibly more fluorescein angiograms.
- The Amsler grid should be closely monitored by the patient in both
the affected and unaffected eye for a change in vision.
- Nutritional supplements can be considered.
It has been found that people with diets deficient in certain "anti-oxidant"
vitamins and minerals may be at increased risk for age-related macular
degeneration. However, a well-balanced diet with the possible supplementation
of a multivitamin will usually prevent such a deficiency. Should extra
doses of these vitamins be taken by those at risk for macular degeneration?
The retina is at risk for light induced damage termed "oxidative"
damage. This damage could possibly lead to macular degeneration. The
retina has relatively high concentrations of anti-oxidant vitamins and
minerals. These substances help to prevent this oxidative damage. These
vitamins and trace minerals include:
- Vitamin A
- Vitamin E
- Vitamin C
- Zinc
- B-Carotene
- Other carotenoids found in foods
- Selenium
Different studies have been done to try to determine
if there is any relationship between blood level and dietary intake
of these substances with age-related macular degeneration (AMD).
- One study showed that high blood levels of Vitamin E were
protective for AMD. Similarly, a combination of high blood levels
of Vitamin C, Vitamin E, and b-carotene was also protective. However,
no protective effect was found with the use of vitamin supplements
themselves!
- Another study found that high blood levels of a combination
of carotenoids, Vitamin C, Vitamin E, and selenium had a reduction
of risk for the "wet" form of AMD. However, the authors
of the study stated that it would be premature to translate these
findings into nutritional recommendations.
- A high dietary intake of zinc was found to be weakly protective
in some early stages of AMD in another study , while the intake of
carotenoids, Vitamin C, Vitamin E, and of nutritional supplements
were found not to be significantly protective.
- High intake of certain foods containing carotenoids not normally
found in vitamin supplements was found to reduce the risk of the "wet"
form of AMD. These foods included spinach, collard greens, kale, mustard
greens, and turnip greens. Intake of supplemental Vitamin A, C, and
E were not found to improve the risk of AMD
Many other studies have been done with varying results. Thus, the verdict
is still out as whether or not supplementation of vitamins and minerals
will help to reduce the risk of macular degeneration. If one has poor
nutrition, however, vitamin supplementation and striving to eat a well
balanced diet may improve the risk.
Many vitamins, especially Vitamins A and E can be stored by the body,
and dangerous side effects can occur when high dosages of these are
consumed. In many people, supplementation with high amounts of zinc
may lead to anaemia. A recent study was terminated because high levels
of B-carotene consumption were found to increase the risk of
lung cancer in male and female smokers. Thus, vitamin supplementation
is not without risk, and one's general physician should be consulted
prior to taking vitamin supplements. Finally, the body regulates the
absorption of many vitamins and minerals. If the body does not need
a particular one of these, it may leave the body undigested.
Remark send :
" I found that through closer examination of this Finland study that a synthetic beta-carotene was used. Should this be pointed
out?? What about the studies that show the wonderful benefits of "Whole Food" carotenoid supplements that contain the full
spectrum of cartenoids. Such studies have been done by the FDA, USDA, various Universities and hospitals. I'm currently
reading a study by the USDA that showed the terrible results from synthetics beta-carotene, but corrected by a "Whole
Food" carotenoid supplement . Would it be more truthful to say that synthetic
supplements in general are not proving any more beneficial that a good diet?"
