October 22, 2018

Female doctor examining adult male patient

Those of us who examine eyes every day are very aware of how much we can learn about  your health with each look inside. The eye is unique in that it is very complex and connected with the rest of the body, yet it is easy to view non-invasively.

For hundreds of years, doctors and scientists have used lenses and instruments to examine the inside of the eye and we can now create incredibly detailed images that allow us to diagnose not only eye disease, but other conditions as well. A very exciting example of this is new research into the early detection of Alzheimer’s Disease.

Scientists have known for some time that the brains of Alzheimer’s patients undergo changes during the course of the disease. Studies of brains from the deceased show the presence of certain proteins and molecules (or “biomarkers”) that don’t appear in large numbers in the non Alzheimer’s population. We don’t know for sure if these biomarkers actually cause the loss of cognitive function or if they are a side effect, but we do know that there is a link. Finding biomarkers in people before they start suffering from cognitive decline could allow for earlier treatment.

Unfortunately, finding these biomarkers in the brains of living people is very difficult, invasive, and expensive. It turns out though, that the retina, which is the lining of the inside of the eye, contains nerves that connect directly to the brain. As researchers have found ways to examine the retina in more detail, they have begun to find evidence of some of the biomarkers present in Alzheimer’s patients.

One research group at the University of Waterloo uses the polarization of light to create a scanning microscope that can take pictures of deep layers of the retina. Using this technology, they have been able to detect a certain biomarker called Beta Amyloid protein. Their theory is that if the amount of Beta Amyloid increases over time, it may help us diagnose and treat Alzheimer’s disease before symptoms begin to appear.

1.Beta Amyloid plaques of various sizes in different layers of retinal tissue
1. Beta Amyloid plaques of various sizes in different layers of retinal tissue

Another Canadian team, called the Optina group, uses a different technique called Hyperspectral Retinal Imaging to create multiple layered images of retinal tissue that can be examined for the presence of biomarkers.

Also, a separate study at Washington University has shown that the retina’s blood supply can be reduced in otherwise healthy patients who happen to have biomarkers. Using technology known as OCTA, anyone’s blood supply can be monitored for changes over time to see if there is risk of developing Alzheimer’s disease. What is exciting about this work is that OCTA is already becoming widely available in many optometry offices.

Spectral domain OCT Angiography (Image courtesy of Topcon Inc.) .Two-Photon Microscopy to Visualize Amyloid-Beta Plaques in Retinas from Alzheimer’s Disease - Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/TPEF-images-containing-Ab-deposits-in-different-human-retinal-tissues-samples-1-4_fig2_321724183 [accessed 7 Sep, 2018]
Spectral domain OCT Angiography (Image courtesy of Topcon Inc.) & Two-Photon Microscopy to Visualize Amyloid-Beta Plaques in Retinas from Alzheimer’s Disease – Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/TPEF-images-containing-Ab-deposits-in-different-human-retinal-tissues-samples-1-4_fig2_321724183 [accessed 7 Sep, 2018]

These examples show that there is a good chance that someday, optometrists using retinal imaging will be able to assess your risk of developing cognitive impairment or Alzheimer’s disease. Although more study is needed before this ability will become widespread, it is another reminder of how your optometrist can use your eyes as windows into your overall health.

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About the Author
Dr. Shawn Charland

Dr. Shawn Charland graduated from the University of Waterloo, School of Optometry in 1999. He has been practicing optometry since and joined the eyeDOCS team in 2006 and became a partner in 2007. For more information about Dr. Charland and his specialized interests relating to optometry, click here.