Pupil Responses to Light Not Altered in Early-Stage Alzheimer Disease

Pupil responses to colored light stimuli are not significantly different in patients with early-stage Alzheimer disease and, subsequently, do not appear to be a noninvasive way to detect early pathology, according to a small study published online in the Journal of Alzheimer's Disease.

The case-control pilot study included 32 older adults participating in a larger prospective study on early-stage Alzheimer disease. Participants underwent cognitive testing, volumetric brain imaging, and lumbar puncture to separate them into two groups: older adults with cognitive impairments and biomarker-confirmed Alzheimer disease pathology (early-stage Alzheimer disease), and older adults with normal cognition and a normal cerebrospinal fluid biomarker profile (control subjects). 

In 16 participants with early-stage Alzheimer disease and 16 healthy controls, researchers using a portable chromatic pupillometer to quantify pupil responses to red and blue light stimuli intended to activate cone photoreceptors and melanopsin ganglion cells. 

Pupil size at baseline was significantly smaller in participants with early-stage Alzheimer disease, researchers reported, and pupillary contraction amplitude to red and blue lights was also smaller. However, the difference between participants with Alzheimer disease and control subjects was not statistically significant. Post-illumination pupillary response, meanwhile, was not different between the two groups. 

“Compared to healthy controls, we found only a smaller resting size of the pupil in patients with early Alzheimer’s disease,” researchers wrote. “The pupillary dynamics to light stimulation remained relatively preserved.” 

—Jolynn Tumolo

Reference:

Kawasaki A, Ouanes S, Crippa SV, Popp J. Early-Stage Alzheimer's Disease Does Not Alter Pupil Responses to Colored Light Stimuli [published online ahead of print, 2020 May 11]. J Alzheimers Dis. 2020;10.3233/JAD-200120. doi:10.3233/JAD-200120