Researchers from the Cedars-Sinai Medical Center, United States, may have found a scientific validation to an old adage, but with a slight change: that the eyes are the window to our health.
In their quest for a conclusive diagnosis of Alzheimer’s disease, they have found that the eyes can provide valuable insights into the condition.
The study findings published in the journal Acta Neuropathologica reveal how Alzheimer’s disease or AD, affects the retina, particularly in the early phases of cognitive decline.
The findings are significant. Currently, there is no definitive diagnostic test for Alzheimer’s, and the available treatments can only slow its progression.
The researchers state that their findings might help develop advanced non-invasive detection and monitoring for Alzheimer’s based on eye imaging techniques.
“Clear signs of Alzheimer’s disease pathology are detected [in the retina] at the earliest stages of functional/cognitive impairment,” Dr Maya Koronyo-Hamaoui, senior author of the study, tells Happiest Health.
Alchemy of Alzheimer’s Disease
Alzheimer’s disease is a condition that affects the brain and the nervous system, leading to a gradual deterioration in memory and cognitive abilities.
The researchers used the inherent connections between the eye and the brain for the detection. Changes in the eye could indicate a deeper problem, specifically in the brain.
“Because these changes correspond with the detection of changes in the brain and can be detected in the earliest stages of impairment; they may lead us to new diagnostics for Alzheimer’s disease and a means to evaluate new forms of treatment,” says Dr Keith L Black, co-author of the study in a statement.
Looking AD in the eye
The retina is situated at the back of the eye and is connected to the central nervous system. As the brain develops, both the optic nerve and the retina are linked to it and form a pouch at the rare end of the brain. This implies that any changes in the central nervous system could reflect in the retina and be observed in the eye. Therefore, the eyes could serve as a window to study the progression of Alzheimer’s disease.
The researchers examined the changes in the retina to find the connection between the brain and cognitive functions in people with AD.
They collected retinal and brain tissue samples from deceased donors who had normal cognitive function, mild cognitive impairment (early stages of Alzheimer’s) and advanced stages. An analysis revealed an excessive presence of amyloid beta 42, a protein known to aggregate and form plaques.
Plaques disrupt brain function. The researchers found the amyloid beta proteins accumulated in the bridge connecting the optic nerves and the retina.
First to study AD through eyes
“Our study is the first to provide in-depth analyses of the protein profiles and the molecular, cellular, and structural effects of Alzheimer’s disease in the human retina and how they correspond with changes in the brain and cognitive function,” says Dr Koronyo-Hamaoui.
The researchers also found a significant increase in the astrocytes and microglial immune cells around these amyloid beta plaques. Typically, microglial cells are low in numbers and clear the amyloid beta proteins from the retina and the brain. However, in the Alzheimer’s disease and cognitive impairment samples, microglial cell counts were 80 per cent higher than normal.
This excessive accumulation of proteins triggered an intense immune response, resulting in inflammation in the surrounding tissues and causing cell and tissue death.
Reading AD stages through eyes
To confirm their findings, the researchers compared these retinal changes in different stages of Alzheimer’s and the cognitive status of the donors. They found that these changes were also evident in tissue samples of people with normal cognitive function but slight impairments in their brains.
This suggests that these changes serve as early indicators of an impending cognitive decline. “These changes in the retina correlated with changes in parts of the brain called the entorhinal and temporal cortices, areas crucial for memory, navigation, and the perception of time,” says Yosef Koronyo, co-author of the study.
The study opens avenues for effective interventions and treatments that can make a difference in the lives of millions affected by Alzheimer’s.
Also Read to have an in-depth Understanding Alzheimer’s disease.
