Ocular tremor in Parkinson's disease is due to head oscillation

Abstract

Background: We investigated the origin of a recently reported ocular microtremor in patients with Parkinson's disease (PD).

Methods: Eye movements were recorded in 2 unselected patients with PD. Two recording techniques were used to control for artifacts: infrared video-oculography and infrared scleral reflection techniques. Head movements were also recorded with 2 different accelerometers.

Results: We recorded ocular oscillations in both patients (microtremor). Ocular tremor was accompanied by a recordable (but clinically nonvisible) head tremor of equal fundamental frequency and high coherence with both the eye oscillation and a recordable limb tremor. The eye movements were in the opposite direction to the head oscillation (ie, compensatory) and were suppressed by head restraint. There was no subjective oscillopsia, nor ocular tremor on fundoscopy.

Conclusions: The "ocular tremor" observed in patients with PD disease is a compensatory eye movement secondary to transmitted head tremor, in agreement with clinical wisdom that these patients do not report oscillopsia.