Progressive bradykinesia and hypokinesia of ocular pursuit in Parkinson’s disease
- Dr GR Barnes, MRC Human Movement and Balance Unit, Institute of Neurology, Queen Square, London WC1N 3BG, UK. Telephone 0044 171 837 3611 ext 3069; fax 0044171 278 9836; email g.barnes{at}ion.ucl.ac.uk
- Received 6 May 1998
- Revised 6 November 1998
- Accepted 22 December 1998
Abstract
OBJECTIVES Patients with Parkinson’s disease characteristically have difficulty in sustaining repetitive motor actions. The purpose of this study was to establish if parkinsonian difficulty with sustaining repetitive limb movements also applies to smooth ocular pursuit and to identify any pursuit abnormalities characteristic of Parkinson’s disease.
METHODS Ocular pursuit in seven patients with moderate to severe bradykinesia predominant Parkinson’s disease was compared with seven age matched controls. Predictive and non-predictive pursuit of constant velocity target ramps were examined. Subjects pursued intermittently illuminated 400/s ramps sweeping to the left or right with an exposure duration of 480 ms and average interval of 1.728 s between presentations. To examine for any temporal changes in peak eye velocity, eye displacement or anticipatory smooth pursuit the 124 s duration of each record was divided into four epochs (E1, E2, E3, E4), each lasting 31 s and containing 18 ramp stimuli. Three test conditions were examined in each subject: predictive (PRD1), non-predictive (NPD), and predictive (PRD2) in that order.
RESULTS Both patients and controls initiated appropriate anticipatory pursuit before target onset in the PRD1 and PRD2 conditions that enhanced the response compared with the NPD condition. The distinctive findings in patients with Parkinson’s disease were a reduction in response magnitude compared with controls and a progressive decline of response with stimulus repetition. The deficits were explained on the basis of easy fatiguability in Parkinson’s disease.
CONCLUSIONS Ocular pursuit shows distinct anticipatory movements in Parkinson’s disease but peak velocity and displacement are reduced and progressively decline with repetition as found with limb movements.
