Opposite effects of l-dopa and DBS-STN on saccadic eye movements in advanced Parkinson's disease

Abstract

Objective: To assess the effects of l-dopa and deep brain stimulation of the subthalamic nucleus (DBS-STN) on saccadic eye movements in patients with Parkinson's disease (PD).

Methods: Visually and internally guided horizontal saccades were evaluated using a saccadometer in 64 patients with advanced PD and 48 healthy controls. Forty-four pharmacologically treated patients were assessed in their "med-off" (OFF) and "med-on" (ON) status, whereas 20 DBS-STN treated patients were assessed in their "med-off, stim-off" (OFF) and "med-off, stim-on" (ON) status.

Results: In all PD patients the saccades in the OFF status were delayed, slower and smaller (p<0.01) than in controls. In pharmacologically treated patients all studied parameters showed tendency to worsen in the ON status as compared to the OFF status. In contrast, activating DBS-STN showed tendency to improve all studied parameters. Comparison of the studied saccade parameters between the ON status of DBS-STN treated patients, ON status of the pharmacologically treated patients and the controls showed that 73% of these parameters in the DBS-STN treated patients were similar as in the controls. While in the pharmacologically treated patients only 26% of these parameters were similar as in the controls.

Conclusion: This prospective study comparing the influence of l-dopa and DBS-STN on saccades in advanced PD showed contrasting results between these two treatments; the majority of the studied parameters in patients on DBS-STN were similar as in the controls.

Keywords: Deep brain stimulation; Levodopa; Parkinson's disease; Saccade; Subthalamic nucleus.