When our environment darkens, the pupils open up to let in more light.

Pupils also dilate when you’re feeling scared or threatened, or when you’re looking at someone you’re physically attracted to. The use of certain medications or recreational drugs can dilate your pupils as well.

But there’s another reason your eyes dilate, and it’s one doctors may be able to take advantage of in the prevention and treatment of Alzheimer’s disease.

The latest research suggests that the way your pupils dilate may be a sign of the onset of Alzheimer’s disease long before the tell-tale symptoms of forgetfulness and confusion appear.

The old adage, “The eyes are the windows into the soul,” can now include the words, “…and the brain.”

Eye Changes Reflect Brain Changes

Scientists have long considered the eyes as an extension of the brain. For many years now they’ve been conducting research to see if any changes take place in the eyes that could signal the development of Alzheimer’s disease years later.

Their findings are telling.

Years before Alzheimer’s develops, patients have thinner retinas, fewer blood vessels within their eyes, and decreased retinal blood flow. Interestingly, deposits of amyloid beta proteins that occur in the brain are also found in the neural layers of the retina, as well as the lens.

The hope is that a simple, accurate, non-invasive eye test will, in the near future, be used to detect Alzheimer’s disease at an early stage.

But rather than peering into the eyes with high-tech scanning equipment, researchers at the University of California, San Diego (UCSD) have found a simpler way to predict the onset of Alzheimer’s.

Pupils Widen with Greater Effort

Their test involves measuring how quickly, and by how much, the pupils dilate while taking a cognitive test.

In their study, published in the journal, Neurobiology of Aging, they looked at changes in pupil size driven by an area of the brainstem called the locus coeruleus (LC). A decade ago, degenerative changes in the LC were found in the earliest stages of Alzheimer’s disease.

Although amyloid beta build-up in the brain may be the best-known hallmark of Alzheimer’s, the misfolded and abnormally shaped tau protein is actually the earliest occurring known biomarker for the disease, as we’ve discussed before in numerous articles.

And guess where this tau first appears?

In the LC.

By the way, the LC is best known for regulating physical arousal, but it also plays an important role in modulating cognitive function.

In an earlier study by the UCSD team, pupil dilation during a cognitive task in people with mild cognitive impairment (MCI) reflected the greater compensatory effort involved in neural systems that were functioning less effectively.

In other words, the more difficult a problem is to solve, the greater the pupils expand, and the iris, the colored portion of the eye, contracts.

Interestingly, this was the case even when test results in cognitively healthy individuals were no better than the ones with MCI.

An Early Screening Tool for the Genetically At-Risk

The researchers speculated that the same pupil changes would be seen in people who were genetically predisposed to Alzheimer’s.

So, for their latest study they recruited 1,119 cognitively healthy men between the ages of 56 and 66, some of which had the APOE gene, a risk factor for Alzheimer’s. Then, they measured pupil dilation after a problem-solving task.

Their theory was confirmed.

Those with APOE had to make a greater cognitive effort resulting in wider pupils. Lead researcher Dr. William S. Kremen explained, “Given the evidence linking pupillary responses, LC and tau and the association between pupillary response and AD polygenic risk scores (an aggregate accounting of factors to determine an individual’s inherited AD risk), these results are proof-of-concept that measuring pupillary response during cognitive tasks could be another screening tool to detect Alzheimer’s before symptom appear.”

My Takeaway

This is exciting news. Especially since Alzheimer’s disease is difficult to diagnose at times, even after memory loss begins.

If you’re concerned about Alzheimer’s disease, these study results are worth discussing with your doctor. It seems to me that asking your doctor to simply monitor your pupil dilation while you’re undergoing annual cognitive testing, could be of great value in your quest to maintain a sharp memory.

Meanwhile, I’ll keep you posted on any further developments in this area.


  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5808562/
  2. https://www.sciencedirect.com/science/article/abs/pii/S0197458019303215?via%3Dihub
  3. https://health.ucsd.edu/news/releases/Pages/2019-09-10-eyes-windows-to-alzheimers-risk.aspx

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