Up to one in five cases of dementia in older people might be avoided if problems with eyesight are prevented or treated, research has suggested.
According to the World Health Organization, there are about 55 million people living with dementia globally.
However, experts have long stressed such conditions are not an inevitable part of ageing, with recent research flagging 14 risk factors that, if addressed, could together prevent or delay 45% of dementia cases.
But while that work suggested about 2% of dementia cases were attributable to untreated vision loss in later life, a new study – considering a wider range of vision impairments – suggests up to 19% of dementia cases in older people could be attributed to vision impairments.
The researchers, whose work was published in the journal Jama Ophthalmology, said: “The total contribution of late-life vision impairment to dementia may be substantial and warrants further examination to inform dementia prevention strategies.”
They analysed visual function assessments and cognitive function data from 2,767 people in the US aged 65 years and older who had health insurance and who were not in care homes or other facilities.
The team used the strength of association between visual impairment and dementia to calculate the proportion of dementia cases that could be attributed to three types of vision impairments – assuming a causal relationship.
The results suggest about 5% of dementia causes could be attributed to distance vision impairment, about 10% to near vision impairment, and about 15% to problems with contrast sensitivity – the ability to distinguish shade and colour.
The team said that overall, 19% of dementia cases could be attributed to at least one such problem, with the figure higher among people aged 71 to 79, women, and non-Hispanic white people.
“Importantly, more than 90% of vision impairments are preventable or correctable,” they said.
Prof Eef Hogervorst from Loughborough University, who was not involved in the study, said her research has shown poor visual sensitivity could predict dementia 12 years before it is diagnosed.
One possibility, she said, was that a common mechanism might be behind both eye problems and dementia, while another was that problems with vision might mean people are less likely to engage in activities that protect against dementia, such as socialising. A third possibility, she said, was that vision loss might cause dementia because people who use their eyes less have degeneration and less blood flow to the brain.
“Lastly social deprivation and poverty in many countries make it difficult for people to get medical help, appointments and treatment and these are major risk factors for dementia,” Hogervorst said.
Prof Anthony Khawaja of University College London said the study added to the growing evidence that treating or preventing vision impairment may reduce the risk of dementia, and stressed the importance of having eye examinations.
“In the future, a visit to your local optometrist may be an effective screening tool not just for eye diseases but for other common causes of illness [including dementia and cardiovascular diseases],” he said.
However, Dr Thomas Littlejohns of the University of Oxford cautioned the work could not prove vision problems caused dementia, while the study was based on a small population in the US with health insurance – meaning the results may not apply more widely.
“Whilst the jury is still out on whether visual impairment causes dementia, if it does, then it will be in the context of a wide range of other modifiable and non-modifiable risk factors, and taking this into account will be important for reducing dementia risk in the wider population,” he said.
