December 1, 1997
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Researchers at Johns Hopkins have shown that some people with macular degeneration can pass their driver's vision test even though large parts of their central retinas are destroyed by disease.
"In the case of some senior citizens, being able to read letters on an eye chart or pass a driver's test isn't proof they can drive under all conditions," says Janet Sunness, M.D., associate professor of ophthalmology at Wilmer Eye Institute. "Many of these individuals voluntarily restrict themselves to driving only during the day."
Using a device with lasers that light up and stimulate the retina, the Hopkins researchers found that these people are able to adjust how they look at lines of eye charts so healthy parts of their retinas respond to letters.
"People with the advanced, dry (non-bleeding) form of age-related macular degeneration (AMD) can adapt to the destruction of patches of the retina and function adequately in bright light," says Sunness.
The discovery also explains why some people with this disease can read small type, but not large type. In such individuals, there is a small area of healthy retina between larger patches of diseased retina that can be used to read. But large letters, like those used for big newspaper headlines or long words, cannot fit into this area. Instead, parts of these big letters fall into the "blind spots" of the retina and are not recognizable.
The work also showed that in people with AMD, parts of the retina that appear healthy on examination may actually have reduced function, especially in dim lighting, says Sunness.
The study of 74 patients aged 63 to 89 was done using a scanning laser ophthalmoscope, a device that stimulates the retina to "see" words, letters and objects "painted" on the retina by a laser.
Initial results were published in the Oct 1997 issue of the journal Ophthalmology. Sunness's ongoing NIH-funded study of AMD, now in its sixth year, currently includes over 150 patients who are followed annually. The study's most recent findings will be submitted for publication in 1998.