Irregular eye movements may signal pre-dementia condition, study finds

Tracking changes in eye movement could soon allow early detection of mild cognitive impairment, the pre-dementia stage that precedes Alzheimer's disease.

A research team led by Kim Jung-il, a researcher at the Korea Institute of Oriental Medicine, announced Tuesday that eye movement patterns and pupil responses are linked to Alzheimer's-related structural brain changes observed at the mild cognitive impairment stage, using eye-tracking technology.

Mild cognitive impairment is an intermediate stage between normal aging and dementia, in which daily functioning is largely preserved but cognitive decline is observable. Conventional cognitive tests have limitations in detecting the subtle neurological and cognitive changes occurring in the brain.

The research team analyzed eye-tracking data and brain MRI scans from 728 participants — 516 cognitively normal older adults and 212 older adults diagnosed with mild cognitive impairment.

The researchers measured how quickly the eyes moved, how much reaction times varied from one instance to the next, and how pupil size changed before and after a stimulus.

The analysis found that reaction-time variability and the degree of pupil fluctuation were far more precise indicators of early brain atrophy than eye movement speed alone.

In the mild cognitive impairment group, the relationship between structural brain atrophy and eye and pupil signals was completely reversed compared with cognitively normal older adults — a phenomenon the researchers described as a "collapse and overload of the brain's control axis."

Among cognitively normal individuals, eye movements were steadier and more stable as cortical regions governing thought and behavior — such as the frontal lobe — were thicker and healthier. In patients with mild cognitive impairment, damage to the brain's neural networks caused that eye-control function to break down entirely, producing a negative correlation.

While no relationship between brain thickness and pupil response appeared in normal individuals, mild cognitive impairment patients showed a sharp decline in pupil response as the brain thinned. In cases where brain thickness was still maintained, pupils dilated abnormally and fluctuated markedly.

"For early detection of dementia, it is important to capture subtle changes that appear before cognitive decline becomes pronounced," Kim said. He added that the team plans to expand its research beyond Alzheimer's disease and mild cognitive impairment to a broader range of age-related conditions.

The findings were published in the international journal Alzheimer's Research & Therapy.