Alzheimer’s is an insidious brain disorder characterized by slow mental decline that can go unnoticed for decades before symptoms appear, but hidden signs of the disease can appear much earlier.
New research suggests that thinning of a person’s retina, the light-sensitive tissue lining the back of the eye, the middle -age is linked to cognitive performance in early & adulthood.
Though much more research is needed, the team behind this new study say the results could one day pave the way to a simple eye test that could help predict a person’s risk of conditions like Alzheimer, the most common form of dementia.
“Given that we have not been able to treat advanced Alzheimer’s disease and the global prevalence of the disease is increasing, it is really important to identify people in the preclinical phase where we may still have a chance to intervene, is really important,” says Health researcher Ashleigh BarrettYoung from the University of Otago, New Zealand.
People with Alzheimer’s life often with visual disabilities that could contribute to mental confusion, disorientation & social withdrawl, all symptoms that interrupt the daily lives of millions of people worldwide with the world with a disease.
However, this isn’t the first-time scientists have suggested the eyes might be a window to the brain. More than a decade ago, researchers found amyloid beta proteins, the hallmark of Alzheimer’s disease, in the retinas of people with the disease & subsequent eye imaging studies showed that Alzheimer’s patients also had thinner retinas.
A study of 2018 also found strong connections between Alzheimer’s disease and three common eye conditions, including glaucoma & macular degeneration.
While such observed associations are intriguing, the risk factors for Alzheimer’s disease are numerous and varied, so any connection between Alzheimer’s disease and eye health remains a matter of intense study for the time being.
In the new study, the researchers crunched data from the long-running Dunedin Study, which has followed the lives of more than 1,000 babies born in a New Zealand hospital in the early 1970s since their birth.
Five decades later, Barrett-Young & colleagues decided on for their analysis a subgroup of 865 adults who had had eye scans at the age of 45 years, in conjunction with a battery of neuropsychology tests in adulthood and early childhood, as a part of the Dunedin experiment.
The thickness of two different parts of the retina (nerve fiber layers of the retina & cell layers of ganglial) was measured in the scans.
The analysis showed that the participants of the study with thinner retinal layers received a lower score in cognitive performance tests and adults, and when they were children.
However, no associations had been found between retinal thinning and an overall decline in cognitive performance (between childhood & middle age) that could indicate some thing is afoot withinside the brain.
While thinner retinal nerve fiber layers at 45 had been linked to a decline in brain processing speeds since childhood, that could simply be a signal of general aging, and not necessarily connected to Alzheimer’s disease.
“The findings suggest that [retinal thickness] can be an indicator of overall brain health,” says Barrett-Young, who led the study.
Whether an eye test for predicting a disorder as complicated and insidious as Alzheimer’s will ever be possible remains unknown. However, some of previous studies including humans with dementia, not simply healthy adults, have suggested retinal thinning may precede cognitive decline & dementia diagnoses.
But that is a tremendously new field & results were mixed. More research is required to tease apart the order of events, to look whether or not retinal thinning really precedes Alzheimer’s onset, if the changes are secondary symptoms of the disease, or simply reflect aging or other lifestyle factors. All are possibilities.
Despite the odds, the researchers clearly believe that they examine the thinning of the retina as a biomarker of cognitive change, which has been found so far, and the growing burden of Alzheimer’s disease.
Taking into account the routine eye tests are less expensive than the imaging scans of the brain, which are usually used to study the brain health, they would be a costly alternative to monitor brain health changes over time when study futures are stacked.
“In the future,” says Barrett-Young, “those findings should result in [artificial intelligence] getting used to take a typical optical coherence tomography scan, completed at an optometrist, and combine it with different health data to determine your likely risk for developing Alzheimer’s.”
The study was published in JAMA Ophthalmology.