Are the eyes a window into Alzheimer’s risk?

Photo: Nan Palmero via Flickr

Can your eyes predict the onset of Alzheimer’s disease (AD) years before cognitive symptoms appear? Findings in a recent study may hold promise for such early detection, say researchers at the University of California, San Diego.

AD starts altering and damaging the brain years — even decades — before symptoms appear, making early identification of risk paramount to slowing its progression. The study’s researchers believe that measuring how quickly a person’s pupils dilate while taking cognitive tests may become a low-cost, non-invasive method to help screen patients at increased genetic risk of developing Alzheimer’s disease before cognitive decline is noticeable.

Researchers investigating the pathology of AD primarily have directed their attention on two causative or contributory factors: the accumulation of amyloid-beta (protein plaques in the brain) and tangles of a protein called tau. Both have been linked to damaging and killing neurons that can result in progressive cognitive dysfunction.

The new study focuses on pupillary responses, which are driven by the locus coeruleus (LC), a cluster of neurons in the brainstem involved in regulating arousal and modulating cognitive function. Tau is the earliest occurring known biomarker for AD. It first appears in the LC and is more strongly associated with cognition than amyloid-beta, researchers said.

Pupils have been shown to get bigger the more difficult a brain task. The LC drives pupillary response — the changing diameter of the pupils — during cognitive tasks. In earlier work, researchers found that adults with mild cognitive impairment displayed greater pupil dilation and cognitive effort than cognitively normal individuals, even if both groups produced equivalent results. In the latest paper, the scientists link pupillary dilation responses with identified AD risk genes.

More investigation is needed before a definitive cause-and-effect can be established, investigators caution. However, “given the evidence linking pupillary responses, LC and tau and the association between pupillary response and AD risk scores, 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 lead author William Kremen, Ph.D., professor of psychiatry and co-director of the Center for Behavior Genetics of Aging at UC San Diego School of Medicine.

The study was published online in the Sept. 9 issue of the Neurobiology of Aging. Journalists who report on Alzheimer’s disease and dementia may want to tap into these additional resources:

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