Involuntary saccades and binocular coordination during visual pursuit in Parkinson's disease

33 Background. Prior studies of oculomotor function in Parkinson’s disease (PD) have either 34 focused on saccades without considering smooth pursuit, or tested smooth pursuit while 35 excluding saccades. The present study investigated the control of saccadic eye movements 36 during pursuit tasks and assessed the quality of binocular coordination as potential sensitive 37 markers of PD. 38 Methods. Observers fixated on a central cross while a target moved toward it. Once the 39 target reached the fixation cross, observers began to pursue the moving target. To further 40 investigate binocular coordination, the moving target was presented on both eyes (binocular 41 condition), or on one eye only (dichoptic condition). 42 Results: The PD group made more saccades than age-matched normal control adults (NC) 43 both during fixation and pursuit. The difference between left and right gaze positions 44 increased over time during the pursuit period for PD but not for NC. The findings were not 45 related to age, as NC and young-adult control group (YC) performed similarly on most of the 46 eye movement measures, and were not correlated with classical measures of PD severity 47 (e.g., Unified Parkinson’s Disease Rating Scale (UPDRS) score). 48 Discussion: Our results suggest that PD may be associated with impairment not only in 49 saccade inhibition, but also in binocular coordination during pursuit, and these aspects of 50 dysfunction may be useful in PD diagnosis or tracking of disease course. 51