(Reuters Health) – Older women with objective visual impairment are likely to develop dementia or mild cognitive impairment, a secondary analysis of data from the Women’s Health Initiative (WHI) suggests.
Researchers examined data on 1,061 women enrolled in the WHI Sight Examination and WHI Memory Study from 2000 to the present. They looked at incident dementia or mild cognitive impairment (MCI) based on annual cognitive testing and clinical assessment for three thresholds of impaired visual acuity at baseline: 20/40, 20/80, and 20/100 and self-reported visual impairment.
Mean age at baseline was 73.8 years.
Overall, 206 women (19.4%) had self-reported visual impairment and another 183 women (17.2%) had objective visual impairment at baseline. In addition, 42 women (4.0%) were classified with probable dementia and another 28 women (2.6%) were classified with MCI that didn’t progress to dementia.
Compared to women without any visual impairment, women with objective visual impairment at baseline were more likely to develop dementia after a mean follow up of 3.8 years. The hazard ratios for visual acuity of 20/100 or worse, 20/80 or worse, and 20/40 or worse were 5.66, 5.20, and 2.14, respectively.
There are several possible ways that visual impairment might contribute to the development of dementia, said coauthor Dr. Suzann Pershing, an assistant professor of ophthalmology at Stanford University in Palo Alto, California.
“One possibility is that dementia and visual impairment could both result from a common cause – brain and nerve degeneration – since vision relies on functioning nerves that come from the brain, Dr. Pershing said by email. “Another possibility is that reduced visual input leads to reduced brain stimulation, and this deprivation in turn leads to cognitive decline.”
It’s also possible that poor vision makes the brain work harder to do tasks, stressing an already challenged system and accelerating cognitive decline, Dr. Pershing said. Visual impairment may also cause people to be less socially engaged and active, which may also contribute to cognitive decline.
Ultimately, the cause is likely some combination of all of these factors, as well as other risk factors such as vascular damage and diabetes, which often coexist in older adults and can cause eye disease and visual impairment in addition to dementia, Dr. Pershing said.
Women with milder objective visual impairment, with acuity of 20/40 or worse, did not appear to have an increased risk of MCI. They did, however, have an elevated risk of MCI with acuity of 20/80 or worse and with acuity of 20/100 or worse, with hazard ratios of 5.62 and 6.43, respectively.
While women with self-reported vision problems did appear to have a slightly elevated risk of dementia and MCI, the results were not statistically significant.
There were few cases of incident dementia and MCI in the WHI study, leading to wide 95% confidence intervals, the authors note.
While the study did demonstrate a dose-response relationship between the severity of visual impairment and the risk of dementia, results from this study of mostly white and college-educated women might not represent what would happen in the general population, the study team cautions.
“The presence of a dose response between a risk factor and the bad outcome supports the notion that the risk factor actually causes the outcome though does not prove that,” said Dr. Heather Whitson, director of the Duke Center for the Study of Aging and Human Development at the Duke University School of Medicine in Durham, North Carolina.
“The big message for patients is to get regular eye exams and vision assessments,” Dr. Whitson, who wasn’t involved in the study, said by email.
“Some older adults make the mistake of delaying care because they assume gradual vision changes are a normal part of the aging process,” Dr. Whitson added. “Many of the most common causes of vision loss in older adults are curable, and others are at least treatable, especially if caught early.”
SOURCE: https://bit.ly/2Wanrv3 JAMA Ophthalmology, online April 16, 2020.