Experimental support that ocular tremor in Parkinson's disease does not originate from head movement.
BACKGROUND
Our recent report of ocular tremor in Parkinson's disease (PD) has raised considerable controversy as to the origin of the tremor. Using an infrared based eye tracker and a magnetic head tracker, we reported that ocular tremor was recordable in PD subjects with no apparent head tremor. However, other investigators suggest that the ocular tremor may represent either transmitted appendicular tremor or subclinical head tremor inducing the vestibulo-ocular reflex (VOR). The present study aimed to further investigate the origin of ocular tremor in PD.


METHODS
Eye movements were recorded in 8 PD subjects both head free, and with full head restraint by means of a head holding device and a dental impression bite plate. Head movements were recorded independently using both a high sensitivity tri-axial accelerometer and a magnetic tracking system, each synchronized to the eye tracker.


RESULTS
Ocular tremor was observed in all 8 PD subjects and was not influenced by head free and head fixed conditions. Both magnetic tracking and accelerometer recordings supported that the ocular tremor was fully independent of head position.


CONCLUSIONS
The present study findings support our initial findings that ocular tremor is a fundamental feature of PD unrelated to head movements. Although the utility of ocular tremor for diagnostic purposes requires validation, current findings in large cohorts of PD subjects suggest its potential as a reliable clinical biomarker.
Southeast Parkinson's Disease Research, Education, and Clinical Center (PADRECC), Hunter-Holmes McGuire Veterans Affairs Medical Center, Richmond, VA, USA; Virginia Commonwealth University, Department of Biomedical Engineering, Richmond, VA, USA. Electronic address: gitchelg@gmail.com.
George T
GT
Gitchel
Virginia Commonwealth University, Department of Biomedical Engineering, Richmond, VA, USA. Electronic address: pawetzel@vcu.edu.
Paul A
PA
Wetzel
Southeast Parkinson's Disease Research, Education, and Clinical Center (PADRECC), Hunter-Holmes McGuire Veterans Affairs Medical Center, Richmond, VA, USA; Virginia Commonwealth University, Department of Physical Medicine and Rehabilitation, Richmond, VA, USA; Virginia Commonwealth University, Department of Neurology, Richmond, VA, USA. Electronic address: abu.qutubuddin@va.gov.
Abu
A
Qutubuddin
Southeast Parkinson's Disease Research, Education, and Clinical Center (PADRECC), Hunter-Holmes McGuire Veterans Affairs Medical Center, Richmond, VA, USA; Virginia Commonwealth University, Department of Neurology, Richmond, VA, USA. Electronic address: mbaron@mcvh-vcu.edu.
Mark S
MS
Baron
D000328:Adult; D000368:Aged; D015331:Cohort Studies; D053483:Eye Movement Measurements; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000175:diagnosis* / Q000453:epidemiology / Q000503:physiopathology; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology; D012149:Restraint, Physical / Q000379:methods; D014202:Tremor / Q000175:diagnosis* / Q000453:epidemiology / Q000503:physiopathology
Biomarker; Bite plate; Eye movements; Ocular tremor; Oscillopsia; Parkinson's disease