Alzheimer's is a cunning brain disease marked by a slow mental decline that unfortunately can develop unnoticed for decades before prominent symptoms arise. However, hidden signs of the condition might exist during its earlier stages.
New research suggests that thinning of the retina - the light-sensitive tissue that lines the back of human eyes - during middle age is associated with cognitive performance during early and adult life.
Alzheimer's Prevalence and the Human Eye
Although authors of the study say that more research is needed to fortify their theories, the team says that their findings may someday lead towards a simple eye test for predicting a person's risks for conditions such as Alzheimer's, which is the most prevalent form of dementia.
Ashleigh Barrett-Young, co-author of the study and a health researcher from the University of Otago in New Zealand, explains that given that science hasn't been able to treat advanced Alzheimer's and that the prevalence of the disease on a global scale is increasing, the ability to identify people in the preclinical stage may give medicine a chance to intervene, reports ScienceAlert.
People diagnosed with Alzheimer's often live their lives with visual impairments that may contribute to mental confusion, social withdrawal, and disorientation. All symptoms, including memory loss, disrupt the lives of millions of people living with cognitive diseases across the globe.
Over a decade ago, scientists began suggesting that the human eye could serve as a window into the brain. Researchers found amyloid-beta proteins in the eyes of patients diagnosed with the disease. Protein is a known hallmark of the disease. Subsequent eye imaging analysis revealed that Alzheimer's patients also had thinner retinas.
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Thinning of Retina Could Be a Preclinical Sign of Alzheimer's
A recent study published in the journal JAMA Network, titled "Associations Between Retinal Nerve Fiber Layer and Ganglion Cell Layer in Middle Age and Cognition From Childhood to Adulthood," analyzed data from a long-running Dunedin study that followed the lives of more than 1,000 babies born during the early 70's at one hospital in New Zealand since birth.
Fifty years later, Barrett-Young, together with her colleagues, selected a subgroup of 865 adults for their analysis that had eye scans at the age of 45 years, together with a battery of neuropsychology tests during their adulthood and early childhood as part of the Dunedin study.
Then, the team measured via scans the thickness of two vital parts of the retina - the retinal nerve fiber layer and the ganglion cell layers.
The analysis showed that the participants with thinner retinal layers scored lower in cognitive performance tests as children and adults. However, no association has been observed between the thinking of the retinal and the overall cognitive performance decline that might indicate problems in the participants' brains.
Although thinner retinal nerve fibers at the age of 45 have been associated with a decline in brain processing speeds since youth, it may also be a sign of general aging and not necessarily of Alzheimer's disease.
Barett-Young says that the findings of their recent study suggest that the retina thickness could be a simple indicator of the brain's overall health.
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