Prescribing lenses and detecting eye diseases will always remain the work of ophthalmologists. But they may take on an additional role in the future.
That’s because the same abnormal proteins that show up in Alzheimer’s disease can also be found in fluid in the eye. In fact, taking a sample of eye fluid is quicker, cheaper, and safer than many other existing tests to detect Alzheimer’s and other neurological diseases well before symptoms appear. Here’s the story…
Alzheimer’s disease can’t be officially diagnosed until death, which is of little use to the living. So, if the disease is suspected, doctors can look for abnormal proteins in the brain or cerebrospinal fluid of living patients. This can be done through a brain scan or a lumbar puncture (spinal tap), both of which are reasonably accurate indicators.
However, these tests are time consuming, expensive and are only used to diagnose Alzheimer’s at an advanced stage. The latest research shows that a better alternative could be an analysis of the eyes.
What Your Eyes Reveal About Memory Loss
Eyes are extensions of the brain and share the same pre-birth development, so they may be a more practical target to look for abnormalities. This is especially true as eyes may not only provide the opportunity for doctors to make a diagnosis of a disease, but also indicate that trouble lies ahead before symptoms of Alzheimer’s disease appear.
For example, changes found in the retina, retinal blood vessels, pupils and tears have already been demonstrated to show up in the early stages of the disease.
Now, researchers from Boston Medical Center have found another area of the eye worthy of investigation. It’s a watery, gel-like substance that fills the space between the lens and the retina. It’s called the vitreous humor.
Vitreous Fluid Reflects Brain Pathology
The researchers first got a hint that vitreous humor could play an important role in early Alzheimer’s detection in work published in 2019 and 2020. In the first study, 80 patients had their cognition tested. There was a clear association between cognitive function and three Alzheimer’s biomarkers in the vitreous humor.
The second study included 77 men and women having eye surgery for a range of problems. Sixty-eight were cognitively healthy while nine had mild or severe impairment. The researchers detected a marker called neurofilament light (NfL) in the vitreous humor samples of every patient.
As we reported in 2021, NfL is a highly sensitive and very accurate blood marker for the early detection of neurodegenerative diseases. A higher level of this marker in the patients was also associated with higher levels of beta-amyloid and total tau deposits in the vitreous humor.
These studies were the first to show that vitreous fluid reflects pathological changes in the brain.
In a follow up study published in the Journal of Alzheimer’s Disease in May 2023, the Boston team were looking for further confirmation of the importance of biomarkers found in the eye fluid.
Link To Alzheimer’s Confirmed
On this occasion researchers used donated postmortem eyes and corresponding brains from 41 people with pathologically confirmed Alzheimer’s and another neurological disease called Chronic Traumatic Encephalopathy (CTE). This results from repetitive head injuries that most usually occur in those taking part in high impact professional sports like boxing and football.
Findings showed that levels of total tau and another tau marker called ptau231 in vitreous humor were significantly increased in both conditions relative to controls.
Senior author and associate professor in ophthalmology Manju Subramanian, M.D. said, “To our knowledge, this is the first study to investigate the role of vitreous fluid biomarkers and link it to confirmed post-mortem brain tissue pathological examination of Alzheimer’s disease. In addition, this is the first study to find a link between vitreous fluid biomarkers and confirmed CTE.
“Our findings provide further evidence to support the potential role of vitreous biomarkers in early diagnosis and prognostication of diseases like Alzheimer’s and CTE.”
While the research is still in its infancy and more studies are needed before the vitreous fluid test can reach prime time, the findings are promising. One day I’ve no doubt that doctors will be able to routinely diagnose early Alzheimer’s disease through simple screening tests such as this.
The Awakening From Alzheimer’s Team
Association of Cognitive Function with Amyloid-β and Tau Proteins in the Vitreous Humor J Alzheimers Dis (2019) https://pubmed.ncbi.nlm.nih.gov/30856114/
Neurofilament light chain in the vitreous humor of the eye Alzheimers Res Ther (2020) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7500015/
Vitreous Humor Biomarkers Reflect Pathological Changes in the Brain for Alzheimer’s Disease and Chronic Traumatic Encephalopathy J Alzheimers Dis (2023) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10258881/