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What is Macular Degeneration?
Macular Degeneration is a blinding disease which causes the death of cells in
the light-sensitive portion of the eye called the retina. These cells, called
photoreceptor cells, are most severely affected in a specialized region of the
retina called the macula, thus the name Macular Degeneration. The macula is responsible
for what is called "fine acuity vision"; this is the vision that you
use when driving, reading, sewing, watching television or any activity that requires
one to focus on very small objects. Loss of the light-sensitive cells in the macula
has devastating effects on vision and can lead to total blindness.
Who is at Risk?
Macular Degeneration is the leading cause of new blindness in adults over the
age of 60 in this country. The disease also causes less severe but significant
reductions in the ability to see and perform everyday tasks. A study funded by
the federal government's National Eye Institute showed that Macular Degeneration
occurs in approximately one out of five people between the ages of 65 to 74. One
of three people over age 75 in this country will suffer some visual impairment
due to Macular Degeneration.
What are the Treatments for Macular Degeneration?
Currently, there are no treatments that prevent Macular Degeneration or reverse
the loss of vision caused by this disease. The most commonly applied clinical
approach to Macular Degeneration is laser treatment which in some cases can slow
the progression of the disease, but does not restore already lost vision. This
disease usually develops painlessly over a long period, often going unnoticed
in its early stages. It is therefore important to receive regular examinations
by a qualified eye care specialist who will be able to detect the early signs
of Macular Degeneration and prescribe self-diagnostic tests that can be performed
at home.
What is being done at The Center for the Study of Macular Degeneration?
Scientists trained in cell biology, biochemistry and molecular biology are pursuing
research that will provide an understanding of the underlying causes of this blinding
disease. While a number of theories have been proposed, little is known about
the processes responsible for the devastating visual loss associated with Macular
Degeneration. It is the goal of the Center for the Study of Macular Degeneration
to use the tools of modern biotechnology to identify the specific cells, molecules
and genes that are responsible for the disease. This knowledge will then be applied
in the design of new approaches for the early diagnosis of Macular Degeneration
and novel therapies to prevent its development and progression.
What is the difference between the "wet" and "dry" forms
of ARMD?
The "dry" form of ARMD refers to the atrophic form which is characterized,
in its late stages, by the degeneration (i.e. atrophy) of the retina in a region
that includes the macula. "Dry" ARMD develops and progresses slowly
over a period of 5-10 years or longer. Appoximately 85% of the total ARMD patient
population has this atrophic form. The less prevalent, "wet" type of
ARMD is also referred to as neovascular or exudative ARMD. It is characterized
by the ingrowth of new blood vessels from the choroid. "Wet" ARMD progresses
much more rapidly, over a period of weeks or months, and usually results in legal
blindness in the central portion of the visual field.
If I develop "wet" or "dry" ARMD in one eye, will it eventually
affect the opposite eye?
Probably. The fellow eye is at high risk of following suit, but the timing can
vary significantly from person to person.
What are the risk factors associated with ARMD?
The strongest risk factors are:
- Age. The incidence of all forms of ARMD rises steeply with advancing age.
In one large study, ARMD increased from approximately 4% of individuals at 43
to 54 years of age, to 23% in those 75 years or older.
- Drusen. The presence of numerous and/or large drusen, accompanied by specific
pigmentary changes in the macula, is considered to be diagnostic of early atrophic
ARMD.
- Smoking. The incidence of both "wet" and "dry" ARMD is
strongly correlated a history of smoking, and the degree of risk is proportional
to the amount of cigarette consumption.
- Genetic factors. Several studies have demonstrated a high rate of concordance
in the development of ARMD among twins, particularly among identical twins. In
family-based studies, the likelihood of developing ARMD is nearly 20 times higher
if one or both parents have ARMD. It is highly likely that one or more gene alterations
carried by the affected individual increase the susceptibility in his/her offspring.
Current evidence for the following additional risk factors is either weak, conflicting,
or unpersuasive: gender, social class, ethnicity, cardiovascular disease, high
blood pressure, dietary fat intake, cholesterol levels, alcohol consumption, estrogen
levels, light exposure, and circulating levels of vitamins, minerals, and anti-oxidants.
For a more comprehensive discussion of the risk factors associated with ARMD,
see Evans et al, 2001.
If you have drusen, does that mean you will eventually develop ARMD?
Not necessarily. Many individuals with some drusen do not go on to develop the
visual symptoms of ARMD. From a clinical standpoint, drusen must attain a threshold
in numbers, size, and shape for them to become a matter of concern to ophthalmologists.
What does it mean if you have a history of ARMD in your family?
A family history of ARMD means that the probability of acquiring it during your
lifetime are somewhat higher than that of the general population.
How does diet influence macular degeneration?
Several studies now indicate that diets rich in green leafy vegetables, such as
spinach, chard and mustard greens, can reduce the risk of ARMD. These and other
vegetables are rich in certain pigments known as carotenoids. Among these, lutein
and zeaxanthin are two that are highly concentrated in the macula where they may
have effects that protect RPE and/or retinal cells from injury caused by the formation
of peroxides and other toxic byproducts of the visual cycle . Lutein and zeaxanthin
are now widely available as dietary supplements; however, their efficacy when
consumed in this form has not been well studied.
Have vitamins and other nutritional supplements been shown to be effective
as treatments for ARMD?
There have been at least five published trials that have tried to determine whether
dietary supplements, such as vitamins A, C, E or zinc can arrest or prevent the
development of ARMD. Thus far, the results from these small scale studies have
not been encouraging. However, new data from a much larger study called the Age-Related
Eye Disease Study (AREDS) indicates that dietary supplementation with 500 mg of
vitamin C, 400 IU of vitamin E, 15 milligrams of beta-carotene and 80 milligrams
of zinc (as zinc oxide) can reduce the risk of developing advanced ARMD by approximately
25%.
Has excessive exposure to bright light or sunlight been implicated in ARMD?
The collective evidence from at least six studies suggests that lifelong light
exposure is not a significant factor in the development of ARMD. In one study
known as the Cheasapeake Bay study, only a weak statistical correlation was found
in commercial fishermen who spent a considerable period of time on the water during
daylight hours.
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