Your Eyesight Could Be Putting You at Risk of Developing Alzheimer's

A new study suggests staying on top of your eye health could offer a simple avenue for reducing your risks of future brain problems.

A team of researchers led by Johns Hopkins Bloomberg School of Public Health epidemiologist Jason Smith has found improvements to common vision problems could potentially prevent as many as one in five dementia cases in older people.

"Given the increasing prevalence of dementia in the US and globally, addressing modifiable risk factors is a priority for dementia prevention strategies," Smith and colleagues write.

Their study doesn't prove that visual problems cause dementia, only that both these conditions are related. This could mean factors that haven't been considered may be involved in both conditions. But previous research strongly suggests there's more to this link than a whacky coincidence.

A post-mortem investigation of 86 human donors diagnosed with cognitive problems revealed changes in their retina corresponded to changes in regions of the brain responsible for memory and time perception. What's more, some eye conditions seem to be correlated with specific forms of dementia; for example age-related macular degeneration tends to happen alongside Alzheimer's disease, whereas glaucoma instead appears to be tied in with vascular dementia.

"[Vision impairment] is hypothesized to impact dementia risk through similar mechanisms as hearing loss," explain Smith and team, referring to proteins which are associated with neurodegeneration impacting nerves involved in auditory sensing.

Alternatively, it may be that reduced sensory perceptions increase demand on a brain attempting to compensate for the losses, taking resources from other brain areas that need them.

"Sensory loss may lead to depression, social isolation, and/or decreased physical activity, which could cause cognitive impairment," Duke University neurologist Heather Whitson and colleagues explained in a 2018 study.

Which means there's a possibility that addressing vision problems may in turn also mitigate some factors behind dementia.

In the new study, Smith and team used data from 2,767 older patients in the US and found up to 19 percent of dementia cases could be linked to at least one vision problem. These include a loss of sensitivity in detecting contrast, or a loss in near visual acuity – being able to distinguish small details with precision, like text.

Surprisingly, not all impairments present the same level of risk, suggesting some conditions ought to be given priority when conducting assessments. The link between vision and dementia was up to nine times greater when contrast sensitivity was included as a variable, for example, compared with the results of studies that only considered visual acuity.

Loss of contrast sensitivity occurs with conditions like cataracts that require surgical intervention or macular degeneration.

Up to 80 percent of vision impairments can be treated or prevented, with visual rehabilitation still assisting in cases where loss isn't reversible.

The research data did not include several minority groups, meaning the results can't be generalized across all populations. Smith and colleagues also didn't include the impact of using glasses and contact lenses, and suggest this would be a good avenue to explore next.

"Day-to-day visual function of an individual is more likely to have a greater impact on one's cognitive function," they write.

"The total contribution of late-life vision impairment to dementia may be substantial and warrants further examination to inform dementia prevention strategies."

This research was published in JAMA Ophthalmology.