02 August 2024

Untreated sight loss 'a risk factor for dementia’

Experts have added sight loss to a list of risk factors for dementia in a wide-ranging analysis that calls for health systems to make sight tests and vision correction available to everyone, especially in older age.

The Lancet Commission 2024 report on dementia prevention, intervention and care included vision loss as a potentially modifiable risk factor for the first time since its initial report in 2017, after considerable new evidence emerged.

"Increasing evidence supports an association between untreated vision loss and dementia risk and potential modification by treatment," says the report. "We have therefore included visual loss as a risk factor in our analysis. Treatment for visual loss is effective and cost-effective for an estimated 90% of people; however, across the world visual loss is often not treated."

The Commission (27 dementia experts) suggests governments should be ambitious about tackling risk factors for dementia, arguing that addressing the risk factors throughout life could prevent or delay nearly half of dementia cases. The report suggests that if everyone with sight loss was treated, monitored and appropriately managed, dementia's prevalence in the population would be reduced by 2%.

Dementia risk was also proportional to the severity of the vision loss, supporting the hypothesis that vision loss might be a causal factor. The analysis did not include people with cortical blindness linked to posterior cortical atrophy, which is sometimes caused by Alzheimer's disease but misdiagnosed as ocular disease.

Globally, more than 12% of adults aged 50 or older are estimated to be living with avoidable sight loss, including common problems that lenses can correct. The meta-analysis of 14 prospective cohort studies also provides a breakdown of risk associated with specific eye conditions, including cataracts, glaucoma and macular degeneration.

The report's lead author, UCL's Professor Gill Livingston, said: "Our new report reveals that there is much more that can and should be done to reduce the risk of dementia. It's never too early or too late to take action, with opportunities to make an impact at any stage of life."

Vision and high LDL cholesterol are the two new risk factors, adding to 12 previously identified by the researchers, including hearing loss and social isolation.

Among the report's 13 key recommendations is a call to "make screening and treatment for vision impairment accessible for all".

The report acknowledges that some of its recommendations assume a causal relationship between the risk factors and dementia, which may only be true in some cases.

Randomised control trials give the best evidence for causal relationships. However, they are ethically problematic because they require treatments that are proven to be beneficial to be withheld from the control group.

We are lucky to have an advanced primary eye care system in the UK which funds free NHS sight tests for everyone aged 60 and over and helps towards the cost of necessary vision correction for those at higher risk or with limited means. The task for government and the primary eye health sector is to make sure these public health benefits are protected and taken up. Much more needs to be done to raise awareness of these issues and to help people protect themselves and their loved ones.  

More than 900,000 people are estimated to be living with dementia in the UK, and by 2040 this figure is expected to rise to 1.4 million.  Any reduction to that figure made by uptake of eye care should be welcomed and prioritised on public health, ethical and societal cost grounds. Let's hope the new government is up to the challenge. Primary eye care certainly is.