Saccades, pupil response and blink abnormalities in Huntington’s disease patients during free viewing

•We used eye tracking to investigate the effect of early Huntington’s disease on saccadic movements, pupil reaction and blink production.•HD patients showed significant changes in all three behaviors while watching short videos in a free-viewing task.•This suggests brain stem degeneration at an early stage of the disease detectable with a simple free viewing task. Video-based eye tracking was used to investigate saccade, pupil, and blink abnormalities among patients with Huntington’s disease (HD) who watched sequences of short videos. HD, an autosomal dominant neurodegenerative disorder resulting from a CAG mutation on chromosome 4, produces motor and cognitive impairments including slow or irregular eye movements, which have been studied using structured tasks. To explore how HD affects eye movements under instruction free conditions, we assessed 22 HD patients and their age matched controls in a 10-minute video-based free viewing task. Patients with HD experienced a significant reduction in saccade exploration rate following video clip transitions, an increase in pupil reactions to luminance changes after clip transitions, and a significant higher blink rate throughout the task compared to the control group. These results show that HD has a significant impact on how patients visually explore and respond to their environment under unconstrained and ecologically natural conditions. Eye tracking in HD patients revealed saccadic, pupil, and blink abnormalities in early HD patients, suggestive of brain circuitry abnormalities that probably involve brain stem deficits. Further research should explore the impact of these changes on the quality of life of the patients affected by the disease.