Washington
DC- Macular degeneration, the leading cause of blindness in the Western
world, has no cure and no truly effective treatment. Now researchers are happy
to have discovered a treatment that at least slows the development of the
disease in the form of a potent combination of antioxidant vitamins.
The macula is at the center of the retina at the back of the eye. For reasons
that have yet to be understood, sometimes the light-sensitive cells in the
macula break down, resulting in a loss of central vision. In one form of the
disease, the ``wet'' form, new blood vessels form behind the retina causing
additional problems. Some 15 million people in the US alone have macular degeneration.
Symptoms typically begin to appear when people reach their 50s and 60s. Nearly
25% of those over the age of 65 develop the disease. The early symptoms involve
some blurring of vision and gradual loss of central vision. Eventually all
but the outermost peripheral vision is lost.
The Age-Related Eye Disease Study (AREDS) followed 4,757 older volunteers
(55-80 years) with various levels of risk for developing macular degeneration
in 11 clinical centers throughout the United States. Participants received
either 80 milligrams of zinc oxide; an antioxidant combination including 500
milligrams of vitamin C; 400 IU of vitamin E; 15 milligrams of beta-carotene;
the antioxidant combination plus zinc; or a placebo. The ongoing study began
five years ago.
"The Age-Related Eye Disease Study dietary supplements are the first demonstrated
treatment for people at high risk for developing advanced AMD. Slowing the
progression of AMD to its advanced stage will save the vision of many who
would otherwise have had serious vision impairment," said Frederick Ferris,
MD, director of clinical research at the National Eye Institute and chairman
of the AREDS.
The
combination of antioxidants plus zinc received reduced the risk of disease
progression by 25% in people with intermediate macular degeneration or advanced
disease in one eye. The antioxidant combination also reduced the risk of vision
loss associated with macular degeneration by 19%. Antioxidants alone or zinc
alone also provided some reduction in risk. High-risk patients taking zinc
alone saw the risk of progression reduced by 21%, with the risk of vision
loss associated with advanced disease reduced by 11%. Antioxidants alone reduced
the risk of progression by 17% and the risk for vision loss by 10%. No benefit
was seen in those with the early stages of macular degeneration (i.e. those
with few small or medium drusen, no vision loss).
These results suggest that both zinc and antioxidants vitamins are important,
and have additive effects, noted. Dr. Ferris. The mechanisms of action of
the compounds used in this study are not known. The study was undertaken based
on epidemiological observations that people with higher serum levels of zinc
and antioxidants had a lower incidence of AMD. The working hypothesis is that
boosting serum levels with these supplements improves the ability of the retinal
pigment epithelium to digest the cellular waste products that lead to drusen
(small spots of dead tissue on the eye) formation.
ABOVE: The
Amsler Grid. Ophthalmologists use this simple tool to screen for macular degeneration.
A person with AMD who covers one eye and looks at dot in center of grid would
see wavy or distorted lines.
The AREDS study findings are especially important since patients with macular
degeneration currently have few options. Laser treatments appear to provide
benefits to some patients with the rare 'wet' form of the disease. An experimental
surgical approach involving a translocation of the affected macula is also
now being investigated. The AREDS study is the first bit of good news to come
to this field for a long time.
"The supplements are not a cure for AMD, nor will they restore vision already
lost from the disease. But they will play a key role in helping people at
high risk for developing advanced AMD keep their vision," said Paul A. Sieving,
M.D., Ph.D., the new director of the US National Eye Institute.
No Benefit vs. Cataract
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Two Forms of AMD
Dry AMD--Ninety percent of all people with AMD have this type.
The retina becomes diseased, leading to the slow breakdown of the light-sensing
cells in the macula and a gradual loss of central vision.
Wet AMD--Although only 10 percent of all people with AMD have
this type, it accounts for 90 percent of all blindness from the disease.
As dry AMD worsens, new blood vessels may begin to grow and cause "wet"
AMD. Because these new blood vessels tend to be very fragile, they will
often leak blood and fluid under the macula. This causes rapid damage
to the macula that can lead to the loss of central vision in a short
period of time.
SOURCE: NEI
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The AREDS protocol was also designed to evaluate the effects of the nutritional
supplements on the development of cataracts. No reduction of cataract risk
was seen in association with any of the treatment regimens during the seven-year
study.
"At the time the study was planned, laboratory and animal research had suggested
that antioxidants might be of benefit in treating or preventing cataract.
Also at that time, limited epidemiological and clinical trial data suggested
that antioxidants might affect the development of cataract. We were surprised
that we did not see a protective effect over the seven years of the study,"
he said.
It may be that longer treatment or different doses may yet prove of benefit
in this regard, he added.
Side Effects- Not Chicken Soup
A small percentage of participants taking the high dose beta-carotene supplements
reported transient yellowing of the skin. There was a small but statistically
signficant increase in urinary tract infections among those taking zinc."We
are concerned about this. It reminds us that this is not chicken soup we are
talking about. It is important that physicians and patients realize the potential,
if small, for side effects from this treatment," he said.
Copper deficiency anemia is known to occur in association with zinc supplementation
in some patients. For this reason the AREDS protocol included copper in the
regimens of all patients who received zinc. In the current study, a slightly
higher rate of anemia was seen in patients receiving zinc, but it did not
reach statistical significance.The doses of vitamins and minerals evaluated
in AREDS were considerably higher than those usually recommended to the public.
There are numerous potential interactions high-dose dietary supplements and
over-the-counter and prescription medications. Therefore it is important that
these regimens should only be considered in consultation with a primary care
physician or ophthalmologist, emphasized Dr. Ferris.
It should also be noted that 80% of people in this age group probably do
not need to take these supplements because they are not at risk. The important
finding from this trial is the identification of a subgroup of high-risk patients
who could benefit from this treatment, he said.
100,000s Could Be Saved
The high-risk group is a substantial population in its own right. In the
US, six million people would qualify as being at high risk. If all of these
people took the supplements used in this study some 300,000 might be saved
from developing AMD, he emphasized.
The complete findings of the AREDS protocol appear in the October 2001 issue
of Archives of Ophthalmology.
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