For now, diagnosing Alzheimer’s is a tricky affair. It requires an expensive brain scan, a risky spinal tap, or, in most cases, a behavioral assessment by a doctor based on symptoms. However, there may be a much better method soon. A recent study reveals that there are tell-tale alterations in the retina and blood vessels when dementia is present. This discovery may make it possible to detect Alzheimer’s disease very early on just through a simple eye test.
Scientists at the Duke Eye Centre in North Carolina wondered if changes brought on by the disease could be visible in the retina, which is essentially a direct link to the brain. The retina’s job is to convert light into neural signals which it sends to the brain to be processed into understandable images. They thought that if the retina is an extension of the brain it could potentially be like a window into what is happening behind the skull.
“The retina and central nervous system are so interconnected that changes in the brain could be reflected in cells in the retina.” – Rajendra S. Apte
Lo and behold, the scientists found the retina was thinner in people with Alzheimer’s and they had also lost more small blood vessels at the back of the eye, compared to healthy people and those with mild cognitive impairment, a forerunner to dementia. Their findings filled them with hope that surely dementia could be picked up early, before symptoms are present, when there still may be time to reverse or halt the disease through medication or lifestyle changes.
How They Made The Discovery
“We urgently need a test to identify people who might go on to develop dementia, but who aren’t showing any clinical symptoms yet. The very earliest changes in the brain can appear up to 20 years before we see clinical symptoms, so the holy grail would be to identify and treat people the moment these changes start.” – Dr James Pickett, head of research at the Alzheimer’s Society
So, Test They Did
The Study
They compared the retinas of 30 Alzheimer’s patients with an average age in the mid-70s, none of whom exhibited clinical symptoms of Alzheimer’s.
These participants were patients in The Memory and Aging Project at Washington University’s Knight Alzheimer’s Disease Research Center. About half of them had elevated levels of the Alzheimer’s proteins amyloid or tau as revealed by PET scans or cerebrospinal fluid, suggesting that although they didn’t have symptoms, they likely would develop Alzheimer’s. In the other subjects, PET scans and cerebrospinal fluid analyses were normal.
Co-principal investigator Rajendra S. Apte, MD, PhD, the Paul A. Cibis Distinguished Professor of Ophthalmology and Visual Sciences, said:
“In the patients with elevated levels of amyloid or tau, we detected significant thinning in the center of the retina. All of us have a small area devoid of blood vessels in the center of our retinas that is responsible for our most precise vision. We found that this zone lacking blood vessels was significantly enlarged in people with preclinical Alzheimer’s disease.”
Every participant had the same eye test. This new test used non-invasive imaging called optical coherence tomography angiography (OCTA). This technology is similar to what is found in many eye doctors’ offices.
The eye test shines light into the eye, allowing a doctor to measure retinal thickness, as well as the thickness of fibers in the optic nerve. At the same time, there is an added component (specifically added for this study only) called angiography, which allows doctors to distinguish red blood cells from other tissue in the retina.
The other co-principal investigator, Gregory P. Van Stavern, MD, a professor of ophthalmology and visual sciences, said:
“The angiography component allows us to look at blood-flow patterns. In the patients whose PET scans and cerebrospinal fluid showed preclinical Alzheimer’s, the area at the center of the retina without blood vessels was significantly larger, suggesting less blood flow.”
Results
- They were able to detect evidence suggesting Alzheimer’s in older patients who had no symptoms of the disease.
- Of the patients studied, 17 had abnormal PET scans and/or lumbar punctures, and all of them also had retinal thinning and significant areas without blood vessels in the centers of their retinas.
- The retinas appeared normal in the patients whose PET scans and lumbar punctures were within the typical range.
- The study has been published in the journal JAMA Ophthalmology.
In Conclusion
The study’s first author, Bliss E. O’Bryhim, MD, PhD, a resident physician in the Department of Ophthalmology & Visual Sciences, said:
“This technique has great potential to become a screening tool that helps decide who should undergo more expensive and invasive testing for Alzheimer’s disease prior to the appearance of clinical symptoms. Our hope is to use this technique to understand who is accumulating abnormal proteins in the brain that may lead them to develop Alzheimer’s.”
It may be possible one day to screen people as young as in their 40s or 50s to see whether they are at risk of the disease. Although, more studies on patients still need to be done before this eye test can be used as markers for Alzheimer’s risk. Van Stavern said:
“We know the pathology of Alzheimer’s disease starts to develop years before symptoms appear, but if we could use this eye test to notice when the pathology is beginning, it may be possible one day to start treatments sooner to delay further damage.”
