Look through the eyes to spot Alzheimer’s: Fewer blood vessels may be an early sign

Scientists could count blood vessels in people’s eyes to detect early signs of the memory-robbing disease, Alzheimer’s.

A study found that people with early signs of cognitive decline had a noticeably smaller number of capillaries in the back of their eyes than healthy people.

The finding adds to past evidence which suggests the changes in the tiny blood vessels may be a window to changes in the brain.

Research in this field is still in its infancy, but scientists said an eye test could one day be used to spot Alzheimer’s in its early stages.

Northwestern University in Chicago recruited 32 participants who went through brain testing to see how good their memory was.

Those with cognitive decline were matched with people of the same age, gender and race whose cognitive (brain) health was good.

All individuals had eye imaging, and those who had cognitive impairment had fewer capillaries in their retina than those who did not.

The team, led by Dr Sandra Weintraub, published their findings in PLoS One. 

The back of the eye can be seen with new technology called OCT angiography that can show capillary changes in great detail.

It is able to reflect what is going on in the brain, as inflammation damages the small blood vessels, Dr Weintraub told Quartz.

The retina and brain are connected by the optic nerve.

Dr Weintraub said: ‘The retina is a direct extension of your brain. It actually has neuronal cells.’

Senior author Professor Amani Fawzi said: ‘Once our results are validated, this approach could potentially provide an additional type of biomarker to identify individuals at high risk of progressing to Alzheimer’s.

‘These individuals can then be followed more closely and could be prime candidates for new therapies aimed at slowing down the progression of the disease or preventing the onset of the dementia associated with Alzheimer’s.’

Therapies for Alzheimer’s are more effective if they are started before extensive brain damage and cognitive decline has started, Professor Fawzi said.

It’s known that patients with Alzheimer’s have decreased retinal blood flow and vessel density.

But only recently have studies shown that these changes are also present in individuals with early Alzheimer’s or mild cognitive impairment who have a higher risk for progressing to dementia. 

A slightly larger study by Duke Eye Centre in Durham, North Carolina, compared the retinas of 200 people with either Alzheimer’s, mild cognitive impairment (MCI) and healthy people with normally functioning brains. 

Alzheimer’s patients had fewer blood vessels and reduced blood flow compared with both healthy controls and people with mild cognitive impairment. 

A specific layer of their retina – sensitive tissue at the back of the eye – was also thinner. 

But in this study, published in Ophthalmology Retina, there was no difference in blood vessels between MCI and healthy controls.

It wasn’t clear if the retinal changes or the onset of Alzheimer’s came first. 

However, lead author Professor Sharon Fekra, said: ‘If we can detect these blood vessel changes in the retina before any changes in cognition, that would be a game changer.’ 

Alzheimer’s is the most common form of dementia, affecting around 500,000 Britons. Scientists still have not nailed down what causes it and a cure is yet to be found.

The focus of research is on developing techniques which can catch the condition at an earlier stage.

Normally by the time a patient receives a diagnosis of Alzheimer’s, the most common form of dementia, there is irreversible damage causing symptoms of forgetfulness, confusion and difficulty with usual tasks. 

Current diagnostic tools for Alzheimer’s are normally pen and paper tests.