Abstract
The identification of ocular tremor in a small cohort of patients with Parkinson’s disease (PD) had lay somewhat dormant until the recent report of a pervasive ocular tremor as a universal finding in a large PD cohort that was, however, generally absent from a cohort of age-matched healthy subjects. The reported tremor had frequency characteristics similar to those of PD limb tremor, but the amplitude and frequency of the tremor did not correlate with clinical tremor ratings. Much controversy ensued as to the origin of such a tremor, and specifically as to whether a pervasive ocular tremor was a fundamental feature of PD, or rather a compensatory eye oscillation secondary to a transmitted head tremor, and thus a measure of a normal vestibulo-ocular reflex. In this mini review, we summarize some of the evidence for and against the case for a pervasive ocular tremor in PD and suggest future experiments that may help resolve these conflicting opinions.
Highlights
Parkinson’s disease (PD) is a neurodegenerative condition characterized by motor features including bradykinesia, rigidity, tremor, and postural instability [1] and non-motor features such as anosmia, constipation, sleep disturbance, sexual impairment, cognitive impairment, and apathy [2]
We summarize the evidence in support of a pervasive ocular tremor, and the evidence in support of apparent ocular tremor resulting from head oscillation
A well know artifact in eye movement recordings in patients with head tremor is an apparent oscillation of the eye in the oculographic trace, which is reduced during forced immobilization of the head
Summary
Parkinson’s disease (PD) is a neurodegenerative condition characterized by motor features including bradykinesia, rigidity, tremor, and postural instability [1] and non-motor features such as anosmia, constipation, sleep disturbance, sexual impairment, cognitive impairment, and apathy [2]. In a single patient from this series, the authors performed electrophysiological recordings showing that the limb tremor and head tremor were coherent at their fundamental frequencies. Hunker and Abbs examined Parkinsonian rest tremor of the lips, jaw, tongue, and index finger in three PD patients, using electromyography [11]. Given the lack of other reports of ocular fixation instability across decades of eye movement recordings in patients with Parkinsonism, the possible origin of the pervasive ocular tremor generated significant discussion and controversy
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