MONDAY, April 10, 2006 (HealthDay News) -- A new study suggests a possible link between age-related macular degeneration (AMD), a leading cause of vision loss among the elderly, and problems with thinking, learning and memory.
The study was originally designed to see whether high doses of antioxidants and zinc could help prevent AMD, a disease in which the center of the retina deteriorates with age. (That trial found the supplement therapy worked for people at high risk of AMD.)
But the nearly 3,000 elderly participants in the study also took a battery of tests to measure various mental abilities.
They took those tests periodically between 2000 and 2004, also taking tests to measure visual acuity. The vision tests listed each participant in one of four categories, ranging from no AMD to an advanced stage of AMD.
Those who had more severe AMD also had poorer scores on the mental function tests, even when the researchers adjusted for factors including age, sex, race, education, smoking, diabetes and high blood pressure.
The finding appears in April issue of the Archives of Ophthalmology.
The researchers offered a couple of explanations for the findings. AMD and loss of mental ability "are both chronic neurodegenerative diseases affecting an increasing number of persons as they age," they wrote. Therefore, the loss of cells in the brain that reduces mental function and the death of nerve cells in the eye may be a common factor linking both conditions, they said.
Another possible explanation is that progressive loss of visual ability by older people reduces "their capacity to develop and maintain relationships and to participate in activities that may improve their physical, mental and psycho-social well-being," they wrote.
But it's not yet possible to give a definitive explanation, said Traci E. Clemons, the lead author of the report and a statistician with the Emmes Corp. of Rockville, Md., which analyzed the study data. "We just know there is some relationship," she said.
The company's statisticians will continue to analyze data from the study, she said. "The current paper looks at prevalence," Clemons said. "We now are looking more at incidence, the progression of the conditions."
Dr. Neil Bressler, professor of ophthalmology at the Johns Hopkins Wilmer Eye Institute in Baltimore, said previous studies have offered hints of a relationship between AMD and cognitive ability, "but they all have their weaknesses, and this [new study] is only a hint as well."
The cautious statement in the report that these data "suggest" a possible association between AMD and cognition "weakens your confidence that there is an association," Bressler said.
"It's possible, because you would think that if something in your body causes your brain to degenerate, the retina is part of the brain and that would cause the retina to degenerate," he said. "But it could be something else unrelated to the brain problem."
The researchers did try to adjust for factors such as age, "but there may be things they didn't know they should adjust for," Bressler said. Such unknowns "make you unable definitely to conclude that AMD leads to cognitive impairment," he said.
Still, the possible relationship reinforces the need to find the cause or causes of both conditions, Bressler said. "It will give clues to other scientists that if you learn of a cause of cognitive impairment, that might also be causing macular degeneration," he said.
More information
More on AMD is provided by the National Library of Medicine.
