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