Losing the ability to see clearly, and losing the ability to think or remember clearly, are two of the most dreaded, and preventable, health issues associated with getting older.
Now, a new study lends further weight to the idea that vision problems and dementia are linked.
In a sample of nearly 3,000 older adults who took vision tests and cognitive tests during home visits, the risk of dementia was much higher among those with eyesight problems – including those who weren't able to see well even when they were wearing their usual eyeglasses or contact lenses.
The research was published recently in JAMA Ophthalmology by a team from the Kellogg Eye Center at Michigan Medicine, the University of Michigan's academic medical center.
Based on data from a nationally representative study of older adults conducted in 2021 through the U-M Institute for Social Research, it adds to a growing pile of studies that have suggested a link between vision and dementia.
All of the older adults in the study were over the age of 71, with an average age of 77. They had their up-close and distance vision, and their ability to see letters that didn't contrast strongly with their background, tested by a visiting team member using a digital tablet. They also took tests of memory and thinking ability, and provided health information including any existing diagnosis of Alzheimer's disease or another form of dementia.
Just over 12% of the whole group had dementia. But that percentage was higher – nearly 22% -- among those who had impaired vision for seeing up close.
In addition, one-third (33%) of those with moderate or severe distance vision impairment, including those who were blind, had signs of dementia. So did 26% of those who had trouble seeing letters that didn't contrast strongly against a background.
Even among those with a mild distance vision issue, 19% had dementia.
After the researchers adjusted for other differences in health status and personal characteristics, people with moderate to severe distance vision issues were 72% more likely than those with no vision issues to have dementia.
The gaps were smaller, but still large, for other types of vision impairment -- except mild problems with distance vision, where there was no statistical difference.
Those who had more than one kind of vision impairment were also 35% more likely to have dementia than those with normal vision.
The new study builds on previous studies that had similar findings but relied on self-reported vision abilities rather than objective testing, or that were not representative of the U.S. population.
It also builds on previous work about cataract surgery that showed lower rates of dementia over time in adults who had had their distance vision restored by having surgery.
The authors, led by ophthalmologists Olivia Killeen, M.D., M.S. and Joshua Ehrlich, M.D., M.P.H., write, "Prioritizing vision health may be key to optimizing both sight and overall health and well-being. Randomized trials are warranted to determine whether optimizing vision is a viable strategy to slow cognitive decline and reduce dementia risk."
But in the meantime, in an accompanying editorial, Sheila West, Ph.D., of the Wilmer Eye Institute at Johns Hopkins Medicine, wrote that the new study adds to accumulating evidence about the link between vision and cognitive issues.
"Equitable access to vision care services that prevent, reverse, or at least stave off progression of loss of sight is a worthy goal regardless of the potential impact on dementia and may be especially critical for those experiencing cognitive decline," she wrote.
The study is based on data from the National Health and Aging Trends Study, which is based at the U-M Institute for Social Research and the Johns Hopkins University Bloomberg School of Public Health.
Last year, Ehrlich and colleagues published a paper in JAMA Neurology that used another ISR-based survey of older adults – the Health and Retirement Study – to estimate the percentage of Americans with dementia whose condition is likely related to their vision loss. They calculated that 1.8 percent of all cases are vision-related, equating to more than 100,000 of the 6 million Americans with dementia. This study suggested that vision impairment should be considered alongside other more commonly recognized modifiable dementia risk factors. That study was funded by the U-M Center to Accelerate Population Research in Alzheimer's (CAPRA) through funding from the National Institute on Aging.
Killeen recently completed the National Clinician Scholars Program at the U-M Institute for Healthcare Policy and Innovation and is now at Johns Hopkins. Ehrlich is an assistant professor of Ophthalmology and Visual Sciences at Michigan Medicine and a research assistant professor at ISR, where he is a co-investigator of NHATS, as well as a member of IHPI.
In addition to Killeen and Ehrlich, the study's authors also include Yunshu Zhou, M.S.
In addition to the National Institute on Aging grant that supports NHATS, and the U-M funding that supports the National Clinician Scholars Program, the study was funded by an unrestricted grant to the U-M Department of Ophthalmology and Visual Sciences by Research to Prevent Blindness.
Killeen, O. J., et al. (2023). Objectively Measured Visual Impairment and Dementia Prevalence in Older Adults in the US. JAMA Ophthalmology. doi.org/10.1001/jamaophthalmol.2023.2854.