Traditionally when you go to your eye doctor, you get checked for refractive errors, glaucoma, cataracts and perhaps Macular Degeneration. Soon you may be able to add something new to that list: Alzheimer’s.
We now know that Alzheimer’s can be detected by a close look at the eye, where doctors can find abnormal proteins, decreased retinal thickness and changes in how retinal blood vessels respond to light stimuli.
This is a huge step forward and would simplify detection.
Alzheimer’s is the most common form of dementia and currently there is no cure. It affects millions of people and the number of victims keeps rising.
But it’s not easy to diagnose and the only definitive way to do so currently is after death when an autopsy may reveal a type of amyloid plaques in brain tissue.
If it could be detected earlier, it could allow patients and their loved ones to plan ahead. It would also allow researchers to improve screening techniques and longer lead times to study how the disease progresses.
The eyes are also a sort of shortcut to the brain and researchers now know that amyloid plaques can form on the back of the retina, although it’s not yet clear just how that happens. It’s possible that it leaks in from cerebrospinal fluid. It’s also possible that amyloid proteins might be synthesized within the eye by neural cells.
Melanie Campbell, professor of optometry and vision science at the University of Waterloo, along with colleagues, has developed a device that can detect plaque more easily.
The technology, called polarimetry, employs polarized light.
Campbell and her team tested the technology on human and canine cadavers and found that it could not only detect amyloid deposits but, uniquely, could easily count and measure their size.
The next phase is clinical tests, but detecting amyloids doesn’t mean a definite diagnosis but rather risk, making it a highly useful screening technique.
Another path to diagnosis is to measure retinal nerve fiber layers (RNFL). The thinner they are, the poorer the cognitive functions of the subject.
Researchers used data collected by the UK Biobank which had data on 500,000 British volunteers aged 40-69.
While many were excluded for various reasons (diabetes or other conditions which affect the retina), others took a series of cognitive tests and some of them repeated the tests after three years.
Researchers found a correlation between thinner RFNLs and declining test scores.
It’s not a perfect answer either – other conditions can cause thin RFNLs - but it is another useful screening technique.
Another method uses flickering light to examine the retinal blood vessels.
In a healthy eye, this causes immediate dilation, but in people with Alzheimer’s, there is a delayed reaction.
None of these are a complete answer, for people at risk, but taken together they show how the eye can be very useful in screening and eventually perhaps diagnosing Alzheimer’s.