With video-oculography (VOG), this study aimed to explore and compare visually-guided and self-paced volitional saccades in Parkinson’s disease (PD) and multiple system atrophy (MSA).

Saccades, rapid eye movements, are divided into two distinct types: reflexive and voluntary. Reflexive saccades are proceeded after a visual, auditory or somatosensory stimulus, while voluntary saccades require internally-generated drive. Each saccade is presumed to require separate neural systems. The voluntary saccades are mediated through higher centers, including frontal eye fields and basal ganglia, in addition to superior colliculus.

We investigated visually guided reflexive and memory guided voluntary saccades by video-oculography in 39 PD and 15 MSA patients. There were no differences for age, sex, and UPDRS motor scores between PD and MSA patients. Two saccades were recorded sequentially, using an infrared eye tracking system (SMI, South Korea).

Comparison of visually-guided reflexive saccades between PD and MSA patients showed no difference in accuracy and peak velocity. 

In self-paced volitional saccades, PD patients produced significantly longer mean accuracy than MSA patients. Pause at the left eccentric position was consistently longer in both PD and MSA, with no statistical group difference.

Volitional saccadic velocity was significantly slower than reflexive saccadic velocity in both groups. Self-paced saccadic accuracy was higher than reflexive saccadic accuracy only in PD, with significant difference. MSA patients did not show significant differences of accuracy between two saccades, although mean accuracy tended to be decreased in volitional saccades paradigm.

In both PD and MSA patients, saccadic eye movements driven by memory-guided voluntary effort had much slower velocity, compared to visually-guided reflexive saccades. PD patients showed hypermetric volitional saccades, meanwhile MSA groups had no difference in accuracy between two saccades.