Prevention of Blindness Society...
YOUR EYES TODAY
NOVEMBER 2001
Dry Macular Degeneration -
Unraveling the Puzzle
Age-related macular degeneration
(AMD) is the leading cause of severe central vision loss among the elderly in
the U.S.A. About 11% of people
over 75 have AMD. There are two
forms: exudative, called wet AMD, and atrophic, called dry AMD. Persons can be affected by either or
both kinds of AMD and it is possible to develop AMD in the second eye once the
first eye has been affected.
At the October 13 Macular
Degeneration Network meeting at Sibley Memorial Hospital, Carol Applegate,
Research Coordinator of Geographic Atrophy Studies at the Johns Hopkins Wilmer
Eye Institute, provided a thorough overview of the dry form of macular
degeneration.
Dry AMD represents 85% of AMD
cases. Some patients may have only
pigmentary changes or drusen, little yellowish spots, which occur in more than
half of the population over 70.
Both cause little or no visual loss. Geographic Atrophy (GA) is a form of advanced dry AMD and is
responsible for about 20% of legal blindness (20/200) from AMD. Geographic - meaning it can be mapped
in the retina, and Atrophy - indicating that cells have died; is slowly
progressive over time. It is
responsible for a significantly large portion of moderate visual loss to the
20/100 level. Patients with GA may
have 20/40 visual acuity because the fovea, the center of the macula, is
preserved, but they may not be able to read or recognize faces because a word
or a face does not ‘fit’ into the tiny central island that is surrounded by a
blind area.
GA tends to spare the fovea, the
very center of the macula responsible for fine vision, until late in the course
of the disease. Small areas of
atrophy begin near the fovea and enlarge and coalesce over a period of years, forming
a horseshoe around the fovea and later a ring. Even though spared, the fovea is compromised in its ability
to see detail. In the end stage,
the fovea itself may become involved.
GA is bilateral in as many as 50 to 65% of patients.
A Geographic Atrophy Study,
conducted at the Wilmer Eye Institute, has determined the average rate of
vision loss of those 20/50 or better to be three lines on an ETDRS (highly
illuminated) chart. An example is
a drop from 20/40 to 20/80. The
enlargement of GA was measured and there was an increase in size of 1.8 mm
squared in two years. On a
research reading test, median rates were 110 words per minute, while the
non-advanced AMD senior could read at 130 words per minute. After two years, GA reading rates
dropped to average 51 words per minute.
Patients with one eye with GA and
another eye with wet AMD have a higher risk (34%) of developing problems
associated with wet AMD in their GA eye than patients with two GA eyes (11%) by
four years.
There are no known guaranteed
preventive measures for either wet or dry macular degeneration. The only documented risk factor that
each of us can control is smoking. Three major population studies determined
that tobacco usage was associated with macular degeneration.
For a copy of the information
presented by Ms. Applegate, call the Prevention of Blindness Society at
202-234-1010.
Source: “Age-related
Macular Degeneration,” Carol A. Applegate, COT, and Janet S. Sunness, M.D. -
Johns Hopkins Wilmer Eye Institute
© 2001
Prevention of Blindness Society of the Metropolitan Area, Washington, DC. All
Rights Reserved.