Elderly adults with poor vision, particularly untreated vision problems, may have a higher risk of developing dementia than those with better vision, a new study suggests.

Researchers found that among 625 older Americans with initially normal cognition, those who said they had poor vision even with corrective lenses were more likely to develop dementia over the next 8.5 years.

During the study period, 168 participants developed Alzheimer’s disease or other forms of dementia. Of those men and women, less than 10 percent had rated their vision as “excellent” at the start of the study. That compared with almost 31 percent of participants who maintained normal brain function over the study period.

On the other hand, about one-quarter of the study participants who went on to develop dementia had rated their vision as “fair” or “poor” at the outset, versus 11 percent of those whose memory and thinking remained intact.

When the researchers looked at the effects of treatment, they found that the highest odds of dementia were among people with poor vision left untreated. The risk was lower when they received some form of eye care.

The findings, published in the American Journal of Epidemiology, do not prove that vision problems contribute to dementia - or that eye care can help slow cognitive decline.

But they do suggest that could be the case, according to lead researcher Dr. Mary A.M. Rogers, a research assistant professor of internal medicine at the University of Michigan in Ann Arbor.

It has long been known that there is an association between dementia and vision disorders, Rogers noted in an interview with Reuters Health. But in practice those problems are often detected and treated after a dementia diagnosis.

The current findings, Rogers said, show that vision problems may precede a dementia diagnosis by years.

It’s not clear why eye disorders and poor vision would contribute to dementia. One possibility, Rogers explained, is the fact that limited vision could keep older adults from being active - whether it’s getting out and walking, reading, doing crosswords or socializing. All of those things, she noted, have been linked to a decreased risk of dementia in older adults.

The findings are based on 625 older U.S. adults who were part of a larger health study begun in 1992.

Overall, Rogers’ team found, study participants who reported “very good” or “excellent” vision were 63 percent less likely to develop dementia over the next 8.5 years than those with poor vision.

The researchers then looked at the combined effects of vision problems with or without treatment on the risk of Alzheimer’s disease specifically. Compared with people who had good vision and at least one visit to an ophthalmologist during the study period, those with poor vision and no visits were more than nine times as likely to be diagnosed with Alzheimer’s.

By comparison, among study participants who had poor vision and at least one ophthalmologist visit, the risk of Alzheimer’s was not significantly increased.

Similarly, men and women with poor vision who had received no eye procedures, such as cataract removal, had a five-fold increase in the risk of Alzheimer’s. That risk was elevated by 2.5 times among people with poor vision who had received such procedures.

According to Rogers, the findings imply that older adults with vision problems should seek treatment - if for no other reason than to improve their sight.

“If you have poor vision, don’t sit on it. Go and see your doctor,” she said. It’s best, Rogers added, to see an ophthalmologist, a medical doctor who can diagnose the range of problems common in elderly adults, such as cataract, glaucoma, macular degeneration and diabetes-related retinopathy.

More studies are needed to replicate the current findings and determine whether vision problems are an actual risk factor for dementia, according to Rogers. With the number of people with Alzheimer’s disease increasing, she said, it is becoming even more important to “take a look at the things we can do to either delay or prevent dementia.”

SOURCE: American Journal of Epidemiology, online February 11, 2010.