Progressive bradykinesia and hypokinesia of ocular pursuit in Parkinson's disease

Objectives-Patients with Parkinson's disease characteristically have diffic ulty in sustaining repetitive motor actions. The purpose of this study was to establish if parkinsonian difficulty with sustaining repetitive limb mov ements also applies to smooth ocular pursuit and to identify any pursuit ab normalities characteristic of Parkinson's disease. Methods-Ocular pursuit in seven patients with moderate to severe bradykines ia predominant Parkinson's disease was compared with seven age matched cont rols. Predictive and non-predictive pursuit of constant velocity target ram ps were examined. Subjects pursued intermittently illuminated 40 degrees/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 temp oral changes in peak eye velocity, eye displacement or anticipatory smooth pursuit the 124 s duration of each record was divided into four epochs (El, 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 pursu it before target onset in the PRD1 and PRD2 conditions that enhanced the re sponse compared with the NPD condition. The distinctive findings in patient s with Parkinson's disease were a reduction in response magnitude compared with controls and a progressive decline of response with stimulus repetitio n. The deficits were explained on the basis of easy fatiguability in Parkin son's disease. Conclusions-Ocular pursuit shows distinct anticipatory movements in Parkins on's disease but peak velocity and displacement are reduced and progressive ly decline with repetition as found with limb movements.