Age-related macular degeneration (AMD) develops when the macula, the portion of the eye that allows people to see in detail, deteriorates. AMD is a leading cause of irreversible vision loss in elderly Americans, according to background information in the article. Cognitive impairment also affects many older adults, reducing their ability to function independently.
The Age-Related Eye Disease Study (AREDS) Research Group examined the relationship between vision problems and cognitive impairment in 2,946 patients enrolled in AREDS, an 11-center study of AMD and age-related cataracts. Between July 2000 and March 2004, the patients took a series of six tests to gauge their cognitive function. Participants' visual acuity (sharpness) was measured every year, and the progression of AMD was assessed and categorized at regular intervals throughout the study using photographs of the retina. Category 1 indicates no AMD and Category 4 is the most advanced stage.
At the time they took the test, 23 percent of the participants were classified as AMD Category 1, 29 percent Category 2, 26 percent Category 3 and 22 percent Category 4. In addition, 72 percent had 20/40 vision or better, 18 percent had worse than 20/40 vision in one eye and 10 percent had an overall visual acuity of less than 20/40. Those who had more severe AMD had poorer average scores on the cognitive tests, an association that remained even after researchers considered other factors, including age, sex, race, education, smoking, diabetes, use of cholesterol-lowering medications and high blood pressure. Average scores also decreased as vision decreased.
There are several possible explanations for these associations, the researchers write. "Age-related macular degeneration and cognitive impairment are both chronic neurodegenerative disorders affecting an increasing number of persons as they age," the authors write. AMD and cognitive impairment also may develop along similar pathways. "For example, the main common characteristic of these diseases is the loss in cells of the nervous system," they continue. Degeneration of the optic nerve and the retina may lead to problems with both vision and cognition.
"In addition, it has been hypothesized that the relationship between visual and cognitive impairment is based on the influence of visual impairment on the level and quality of interactive experiences of older adults, thus reducing their capacity to develop and maintain relationships and to participate in activities that may improve their physical, mental and psychosocial well-being," the authors write. "It has been postulated that vision impairment affects cognitive performance by reducing the level of participation in these types of stimulating activities and thus leads to a decrease in brain reserve. The lack of activity may exacerbate cognitive impairment indirectly if it predisposes a person to depression and social isolation."
(Arch Ophthalmol. 2006;124: 537-543. Available to the media pre-embargo at www.jamamedia.org.)
Editor's Note: This study was supported by contracts from the National Eye Institute, the National Institute on Aging and the National Institute of Neurological Disorders and Stroke, National Institutes of Health, Department of Health and Human Services, Bethesda, Md.