Saccade and pupil changes in children recovering from opsoclonus-myoclonus ataxia syndrome reveal midbrain alterations in oculomotor circuits.

Objective: This study measured eye movements in children with a history of opsoclonus-myoclonus ataxia syndrome in order to identify abnormalities in saccade and pupil behavior that map onto specific alterations in brainstem pathways. Methods: We used video-based eye tracking while participants freely viewed 10 min of short (2-4 s) video clips without instructions. Clip transitions represented a large visual perturbation and we quantified multiple characteristics of saccade and pupil responses following these transitions in 13 children recovering from opsoclonus-myoclonus and 13 healthy, age-matched control participants. Results: The frequency of saccades and distribution of fixation durations differed between the groups. Following the clip transitions, children recovering from opsoclonus-myoclonus ataxia syndrome exhibited longer time to initiate saccades, leading to a delay in harvesting visual information. Clip transitions to lighter clips produced similar pupil constriction responses in the two groups. However, clip transitions to darker clips produced dilation responses that were initiated earlier and of greater magnitude in opsoclonus-myoclonus ataxia syndrome, suggesting removal or suppression of a signal that delays dilation. Interpretation: Children with a history of opsoclonus-myoclonus ataxia syndrome demonstrated key abnormalities in saccade and pupil metrics. We propose a novel hypothesis in which dysfunction in the pathway from the superior colliculus to the mesencephalic and pontine reticular formation that houses the saccade and pupil premotor circuits could produce these results.