Is your distance vision bad? Your risk of getting dementia could be higher, study suggests
- One-third of people with moderate or severe distance-vision impairment, including those who were blind, who took part in a recent study had signs of dementia
- Cataracts, glaucoma, optic nerve problems and macular degeneration can all increase your dementia risk, which is why getting your eyes tested regularly is vital
The first indication that my mother had had a stroke was evident in her eyesight.
She developed a condition called hemianopia, in which half the field of vision is lost because of damage to the optic nerve in the brain.
In her case, the loss was on the left.
To try to mimic what she could see post-stroke, I covered my left eye with the palm of my hand. When her therapist showed me a simulation on an iPad of how compromised her sight was, though, I discovered my crude attempt didn’t correctly convey her loss of vision: it was much worse than that.
If you cover an eye that sees well with a hand, the uncovered eye is still able to track to the left and the right. Hemianopia usually affects both eyes – mum was entirely blind to her left side.
If someone had approached her from that side, she wouldn’t have seen them until they were directly in front of her.
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There were a number of factors that may have contributed to my mother’s later diagnosis of dementia. Her compromised sight, it turns out, could have been one of them.
A recent study of 3,000 older adults by the University of Michigan, Ann Arbor in the United States found that 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 glasses or contact lenses.
They found that one-third of those with moderate or severe distance-vision impairment, including those who were blind, had signs of dementia.
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Even among those with a mild distance-vision issue, 19 per cent had dementia. Those who had more than one kind of vision impairment were 35 per cent more likely to have dementia than those with normal vision.
The findings mirror those of previous studies, including one which found that elderly people who underwent cataract removal surgery had a 30 per cent lower risk of developing dementia compared with participants who did not have such surgery.
Cataracts are opacities on our eye lenses that blur our vision and, if not treated, lead to blindness.
With decreased visual input into the brain, there may be direct alteration in the brain’s anatomy that predisposes a person to cognitive decline and dementia
There are several hypotheses as to why loss of vision might be a risk factor for dementia, says ophthalmologist Joshua Ehrlich, a lead author of the study.
“In some cases, there may be a common neurodegenerative or vascular cause of vision loss and dementia. Also, vision loss is associated with decreased physical activity and social engagement, both of which are risk factors for dementia.
Ehrlich says the study tested only visual function, and did not include an examination to determine the causes of vision problems.
“We know that uncorrected/under-corrected refractive error (an unmet need for glasses or contact lenses) and cataracts are the most common and most easily reversible causes globally,” he added.
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Vision problems triggered in other ways, such as from glaucoma and age-related macular degeneration, may be irreversible, but are often preventable with early detection and treatment.
Ageing is the most significant risk factor for sight-compromising conditions, Chan says. Aside from cataracts, other common eye diseases are glaucoma, and age-related macular degeneration, or AMD.
AMD affects more people because the ageing population is on the rise, he says. It does not cause total blindness, but rather a central scotoma – or blind spot – in our field of vision.
Glaucoma is often referred to as the “silent thief of sight”, he says, because it is asymptomatic. Chan recalls seeing patients for the first time who have come to him with late-stage glaucoma.
People with glaucoma suffer from progressive loss of field of vision – which usually starts from the periphery, or outer edge. Despite this, their visual acuity can remain unchanged, meaning many can still see perfectly with 20/20 vision.
“Because the field of vision overlaps significantly, many patients can have substantial field loss before they notice anything,” Chan says.
This is why glaucoma screening is so crucial, he stresses, especially for high-risk individuals – which include people with a family history of glaucoma.
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Those over the age of 50 should be having eye tests every year. A dilated eye exam can help diagnose conditions like glaucoma and AMD before they become dangerous, he says.
Aside from acute angle closure glaucoma, which presents with a sudden onset of severe eye pain or a headache that comes with blurred vision, seeing rainbow-coloured halos around lights, and vomiting, these conditions are usually painless, Chan says.
Any symptoms are usually gradual, so you should be on the lookout for progressive blurring of vision, photophobia (increased blurriness under bright conditions), metamorphopsia (distortions in vision); diplopia (seeing double); patchy visual field loss and micropsia/macropsia (in which one eye sees things smaller/larger in comparison to the other).
Seeing your ophthalmologist regularly, it turns out, is not just about making sure you can read well enough or even see well enough. It might even be about protecting your brain.
