Link between eye health and dementia

Otago Daily Times

26-04-2025

Researchers have uncovered a link between eye health and dementia using data from the Dunedin Longitudinal Study, which could help identify the cognitive syndrome early.
University of Otago/Ōtākou Whakaihu Waka researcher, Dr Ashleigh Barrett-Young, told RNZ's Saturday Morning programme today that changes to the blood vessels at the back of the eye could indicate someone is at greater risk of developing dementia.
Barrett-Young, co-lead author of the study and a Research Fellow in the university's Department of Psychology, told Susie Ferguson there were two categories of retinal measurements.
"We looked at the thickness of a couple of the cell layers from the retina. These are the same cells that form the optic nerve - they connect directly with the brain.
"And we also looked at the blood vessels at the back of the eye because they're closely related to the blood vessels in the brain."
She said the idea was that if there was any sign of disease in the brain, then it should also be able to be seen in the eye.
The study participants were aged 45 when the data was collected, which Barrett-Young said was usually too young to be diagnosed with dementia.
However, she said co-author of the research, Dr Aaron Reuben, created a comprehensive index of different types of dementia risk-factors including genetic, family history, smoking, physical activity, hearing impairment, blood pressure and a history of head injuries.
Reuben combined them to make a single risk score, and the retinal measurements were checked off against this, Barrett-Young said.
"So we found that both the cellular thickness' and the blood vessel measurements were associated with increased risk for developing dementia based on those risk scores, though the blood vessels did show a stronger association."
Barrett-Young said there were too types of blood vessels at the back of the eye.
"One is arterioles - you can think of them like mini-arteries," she said.
"(It's the) same as when you have heart disease or when you have atherosclerosis. There starts getting build-up in those blood vessels and so they tend to narrow so the blood isn't flowing as well."
On the other side were venuals, which were like "mini veins".
"They tend to be subject to greater inflammation which means they end up widening so that they're not working as effectively either."
The changes taken separately indicated different things but together indicated the blood vessel system was not working as well as it could.
Barrett-Young said it was difficult to know how much more at risk these factors made people, for developing dementia.
"I think we're getting slowly closer to a better answer for that." How AI could help
Barrett-Young said Alzheimer's disease and other dementias begin a long time before any symptoms became apparent, possibly even decades before people noticed cognitive decline.
"Currently Alzheimer's disease and dementia are usually diagnosed based on cognitive tests, including memory tests, things like that.
"But part of the problem is that we all experience some age-related changes in our memory and processing speed over time and that's just completely normal.
"So it takes a while until it's clear that the cognitive decline is beyond a level that is typical of normal ageing and that might suggest that a person has Alzheimer's disease or another type of dementia.
"But that's what makes it really hard to diagnose Alzheimer's disease in the early stages when the damage is only just beginning, and when any interventions we can do, like lifestyle changes, might have the greatest impact."
Barrett-Young said the longitudinal study gave the researchers decades of history on each subject.
She believed artificial intelligence would play a part in helping to use the retina as a biomarker for determining a person's risk of dementia.
"What we're able to tell is that there are really small changes in the eye that we probably wouldn't pick up using your standard optometry or ophthalmology tests but that taking those images and being able to use artificial intelligence may be able to give you an idea of a person's risk for dementia.
"So perhaps in the future AI will be able to tell you whether you're at increased risk of developing Alzheimer's, even possibly years before you have the disease."