Medication adversely impacts visually-guided eye movements in Parkinson's disease

Objective: We examined whether previous inconsistent findings about the effect of anti-Parkinsonian medication on visually-guided saccades (VGS) were due to the use of different paradigms, which change the timing of fixation offset and target onset, or different target eccentricities.

Methods: Thirty-three participants with Parkinson's disease (PD) completed the VGS tasks OFF and ON medication, along with 13 healthy controls. Performance on 3 paradigms (gap, step, and overlap) and 2 target eccentricities was recorded. We used mixed models to determine the effect of medication, paradigm, and target eccentricity on saccade latency, gain, and peak velocity.

Results: First, we confirmed known paradigm effects on latency, and target eccentricity effects on gain and peak velocity in participants with PD. Second, latency was positively associated with OFF medication Movement Disorders Society - Unified Parkinson's Disease Rating Scale (MDS-UPDRS) motor score in PD. Third, medication prolonged latency for the larger target eccentricity across the 3 paradigms, while decreasing gain and peak velocity in the step paradigm across target eccentricities.

Conclusions: Medication adversely affected and was not therapeutically beneficial for VGS. Previous inconsistencies may have resulted from chosen target eccentricity.

Significance: The negative medication effect on VGS may be clinically significant, as many activities in daily life require oculomotor control, inhibitory control, and visually-guided shifts of attention.