The thinning of a person's retina - the light-sensitive tissue that lines the back of the eye - in middle age may be linked to cognitive performance in childhood and adulthood, according to new research.
While research is ongoing, the authors behind this new study believe that the findings could one day pave the way for a simple eye test that can help identify a person's risk of illnesses like Alzheimer's disease, the most common form of dementia.
Alzheimer's disease is a sneaky brain disease characterized by a gradual mental loss that might go unrecognized for decades before symptoms appear, but concealed clues of the disease may be present much earlier.
People with Alzheimer's disease frequently have visual impairments, which may lead to mental confusion, disorientation, and social disengagement - all of which, along with memory loss, disturb the everyday lives of millions of people worldwide.
"Given we haven't been able to treat advanced Alzheimer's, and that the global prevalence of the disease is increasing, being able to identify people in the preclinical stage, when we may still have the chance to intervene, is really important," health researcher Ashleigh Barrett-Young from the University of Otago, New Zealand, said.
Researchers analyzed data from the long-running Dunedin Study, which has monitored the lives of over 1,000 babies born in New Zealand in the early 1970s at a single hospital since their birth.
Barrett-Young and colleagues examined a subgroup of 865 adults who had undergone eye scans at the age of 45, as well as a battery of neuropsychology tests in adulthood and early childhood, as part of the Dunedin experiment.
The scans were used to measure the thickness of two different regions of the retina (retinal nerve fiber layers and ganglion cell layers).
Analysis revealed that participants in the study with thinner retinal layers performed worse on cognitive performance assessments as adults and as children.
However, this is not the first time that scientists have proposed that the eyes could be a window into the brain. Researchers discovered amyloid-beta proteins, the hallmark of Alzheimer's, in the retinas of Alzheimer's patients more than a decade ago, and subsequent retinal imaging studies revealed that Alzheimer's patients also had thinner retinas.
A 2018 study discovered high associations between Alzheimer's disease and three prevalent eye disorders, including glaucoma and macular degeneration.
While such findings are exciting, the risk factors for Alzheimer's disease are numerous and varied, so any links between Alzheimer's and eye health are now being investigated.
Routine eye exams are less expensive than brain imaging scans, which are routinely used to evaluate brain health, so they could be a cost-effective way to track changes in brain health over time - assuming future research is as promising.
The study was published in JAMA Ophthalmology.
