Eye tests could spot signs of Alzheimer’s years before symptoms first appear, new research suggests

A routine eye test could spot signs of Alzheimer’s disease years before symptoms first appear, promising research has suggested.

Experts from City St George’s, University of London say early stage cognitive decline could soon be picked up by an AI tool rolled out in opticians and ophthalmologist offices that measures changes to blood vessels in the back of the eye.

The tool, which is being tested using the health records of more than 500,000 Britons, could help dementia patients be identified and treated before the disease significantly damages their brain.

It comes as pioneering research from scientists in China suggests the thickness of the retina – the light-sensitive tissue that lines the back of the eyes – could also help predict the disease.

Nearly 1 million people are living with dementia in the UK – a figure projected to rise to more than 1.4 million by 2040. The disease is still the UK’s biggest killer, claiming 76,000 lives each year. Last year, The Mail on Sunday and Daily Mail launched its Defeating Dementia campaign, in association with Alzheimer’s Society, to raise awareness, increase early diagnosis, boost research and improve care.

Caused by a build-up of proteins or reduced blood flow in the brain, the condition has no cure.

In 2024, the first medicines capable of slowing Alzheimer’s, lecanemab and donanemab, were approved for use in the UK.

However, NHS chiefs refused to fund these costly infusion drugs because they appeared to only slow the disease’s progression for less than a year. But experts say these medicines – and others like them – could be even more effective if given to patients as soon as they develop dementia – before too much damage is done.

For many Britons, however, the condition is not picked up for years after symptoms begin – with a recent study from University College London finding that it takes patients roughly 3.5 years to be diagnosed.

But now, researchers at City St George’s have found a new approach – looking for signs of cognitive decline during routine eye exams.

Every year, thousands of older adults have photos taken of the back of their eyes to check for changes to the retinal blood vessels – which research has shown are closely linked to ones in the brain and can show signs of neurodegeneration.

Experts believe the retina may predict Alzheimer’s risk because it is part of the central nervous system and connected directly to the brain via the optic nerve.

This makes the eye vulnerable to degeneration in the brain caused by Alzheimer’s disease, including nerve cell loss, inflammation and vascular damage.

Retinal thinning can also be a sign of brain changes such as reduced brain volume and atrophy – a gradual wasting away.

A study published earlier this year by scientists at the Jackson Laboratory in the US found those who had suffered changes to these tiny blood vessels were more likely to have a common genetic mutation known to raise the risk of Alzheimer’s.

They also discovered blood vessels that are more twisted and looped than normal may limit how nutrients and oxygen is transported.

To analyse thousands of images, the City St George’s research team, funded by Alzheimer’s Society, used an AI tool that can measure the exact width and area of the vessels, and found that changes to retinal vessels are strongly linked with lower cognitive test scores.

Misha Ramesh, lead researcher at City St George’s, said: ‘This should help to predict neurodegenerative disease before symptoms begin.’

Last year this newspaper reported that researchers were developing a nose swab test that could spot dementia decades before symptoms begin to show.

The University of Southampton scientists say that if successful, their swab test could provide results ‘in minutes’.