Simple eye and smell tests could be used to spot dementia years before sufferers experience memory symptoms, new research suggests.

Researchers at Moorfields Eye Hospital and the UCL Institute of Ophthalmology found a link between poor cognitive ability – a “clear warning sign” of the early stages of Alzheimer’s –and the thickness of people’s retinal nerves.

In a trial of more than 33,000 participants who had tests on memory, reaction time and reasoning, eye scans showed the nerve fibre layer was “significantly thinner” among those who performed poorly on cognitive tests.

Changes in the brain associated with dementia can begin several years before any memory symptoms appear

The findings, presented at the Alzheimer’s Association International Conference in Toronto, Canada, could be key as doctors believe diagnosing the condition early is “essential” if treatments are to be found that will give people who develop the condition the best chance. Clare Walton, research manager at Alzheimer’s Society UK, said: “Changes in the brain associated with dementia can begin several years before any memory symptoms appear. This research suggests that some of these changes happen in the retina of the eye too, which could give us a relatively easy, non-invasive way to spot them early.Eye tests are fairly common for older people, so there is great potential to incorporate additional tests into their regular check-up.”

While the tests could help with early intervention, it is not expected to be a primary way to diagnose the condition, she added.

Other findings presented at the conference suggest smell tests could help predict cognitive decline and detect early-stage Alzheimer’s disease.