How quickly a person’s pupil dilates while they are taking cognitive tests may be a low-cost, low-invasive method to aid in screening individuals at increased genetic risk for Alzheimer’s Disease before cognitive decline begins.

Alzheimer’s damages the brain years or decades before symptoms appear, so early detection and treatment are critical for preventing the disease progression.

A study published in the journal Neurobiology of Aging suggests that measuring how rapidly the pupil of the eyes dilate while taking cognitive tests may be an alternative, non-invasive, and affordable screening test to detect those who are at higher risk of Alzheimer’s disease before they experience cognitive decline.

The researchers investigated two major contributors to cognitive the disease: the accumulation of a protein plaque, called amyloid-beta, in the brain, and tau tangles.

Why pupillary response signals Alzheimer’s

The study shows that pupillary responses to specific neurons called locus coeruleus are involved in cognitive function and arousal. An early biomarker of AD, tau proteins, first appear in the locus coeruleus. The tau tangles are associated with cognitive abilities more than the amyloid-beta.
The LC stimulates a pupillary response. For example, the pupils will enlarge depending on the complexity of a cognitive task. This follows from a previous study that showed that people with mild cognitive impairment, one precursor to Alzheimer’s disease, showed greater pupil dilation compared to those without any cognitive problems.

In the study, however, the researchers wanted to find the connection between pupillary dilation responses with identified AD risk genes.

Identifying the specific genes associated with the pupillary response factors may improve understanding of the functioning of the LC-NE system

“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,” said Dr. William Kremen, the lead researcher at the University of California San Diego School of Medicine that conducted the study.

Tests rule out diseases with similar symptoms

Tests including scans, blood and urine samples, and psychiatric assessment help rule out other health conditions with similar symptoms. But, confirmation can only be made through an examination of the patient’s brain after death.

“Identifying the specific genes associated with the pupillary response factors may improve understanding of the functioning of the LC-NE system and genetically-mediated factors affecting risk for MCI (mild cognitive impairment) and AD (Alzheimer’s disease),” the researchers conclude in the study.

The new method of detecting AD is a promising diagnostic test to help people with Alzheimer’s disease and their families.