Altered Vergence Eye Movements and Pupil Response of Patients with Alzheimer's Disease and Mild Cognitive Impairment During an Oddball Task.
Level 4 - case-series / case-control
Cross-sectional case-control study comparing physiological responses across clinical and control cohorts
PubMed 34024820 · doi:10.3233/JAD-201301
What was done
Participants (23 healthy controls, 33 patients with mild cognitive impairment [MCI], and 18 patients with Alzheimer's disease [AD]) completed a visual oddball task requiring a button press for target stimuli (red, 20% of trials) versus distractor stimuli (blue, 80% of trials). Vergence eye movements and pupillometric responses were tracked during cognitive processing.
What was found
Participants showed a transient peak vergence response 200 ms post-stimulus. Controls showed a subsequent delayed response to targets but not distractors, whereas MCI and AD patients showed delayed vergence responses to distractors as well. Consequently, the differential vergence response was strong in controls, weak in MCI, and absent in AD. Pupils dilated 500–600 ms after target presentation and slightly contracted after distractors, with this differential pupil response being strongest in the AD group. The abstract reports no numerical metrics, effect sizes, or p-values.
Why it matters
These findings suggest that attention-mediated vergence and pupillary dynamics degrade across the spectrum from MCI to AD, highlighting potential physiological markers for cognitive assessment.
Limits
The study is limited by a small sample size (n = 74 total, with 18 AD patients), a cross-sectional case-control design without prospective follow-up, and the lack of diagnostic accuracy statistics or effect sizes in the abstract.