More Evidence Linking Impaired Vision and Dementia Risk

Why would vision impairment correlate with risk of dementia? The retina is an extension of the central nervous system, so one might think that similar processes of aging and neurodegeneration contribute to both loss of visual capacity and loss of cognitive capacity. But it might also be the case that in the brain, as for muscles, there is a degree of "use it or lose it" taking place over the course of later life. Without stimuli, in other words, the aging brain declines more rapidly. Most of the evidence for an association between visual impairment and cognitive impairment in older individuals doesn't allow us to determine which of these options is the dominant mechanism, however.

Recently, researchers found that one can look at people who did or did not have cataract surgery in order to infer the effects of visual impairment on cognitive function. Mechanisms driving cataract formation should have little in common with mechanisms driving cognitive impairment. Researchers found that cataract induced visual impairment does correlate with cognitive impairment, and removal of cataracts prevents this later loss of cognitive function. This provides strong support for the role of visual stimuli in slowing the pace of brain aging.

Study shows dementia more common in older adults with vision issues

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. 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.

Objectively Measured Visual Impairment and Dementia Prevalence in Older Adults in the US

Estimates of the association between visual impairment (VI) and dementia in the US population are based on self-reported survey data or measures of visual function that are at least 15 years old. Older adults are at high risk of VI and dementia so there is a need for up-to-date national estimates based on objective assessments. This secondary analysis of the 2021 National Health and Aging Trends Study (NHATS), a population-based, nationally representative panel study, included 3,817 respondents 71 years and older.

The weighted prevalence of dementia was 12.3% and increased with near VI (21.5%), distance VI (mild: 19.1%; moderate, severe, or blind: 32.9%), and contrast sensitivity (CS) impairment (25.9%). Dementia prevalence was higher among participants with near VI and CS impairment than those without (near VI prevalence ratio: 1.40; CS impairment prevalence ratio: 1.31) and among participants with moderate to severe distance VI or blindness (prevalence ratio: 1.72) after adjustment for covariates.

Thus in this survey study, all types of objectively measured VI were associated with a higher dementia prevalence. As most VI is preventable, prioritizing vision health may be important for optimizing cognitive function.