Akinesia, hypokinesia, and bradykinesia in the oculomotor system of patients with Parkinson's disease

Abstract

Detailed characteristics of voluntary saccadic eye movement were measured in 14 Parkinsonian patients and 12 age-matched controls by d-c electrooculography (5% attenuation at 450 Hz). Subjects performed rapid, alternating gaze shifts between two fixed visual targets separated horizontally by 25° of arc. On average, the patients took about twice as long as the controls ( p < .001) to complete a cycle of the alternating task. Since the dynamic characteristics of the patients' saccadic movements were normal for the amplitude achieved, the fault was not due to a reduced ability to make fast, coordinated, muscle movements. The slowed performance was found to be due to two main factors: an increased target fixation time manifest as delayed initiation of voluntary movement (akinesia); and increased transit time between targets (bradykinesia) due to the normal delays of about 200 msec between corrective saccades which were necessitated by an abnormal ( p < .001) tendency to undershoot the target (hypokinesia). The marked akinesia found in this investigation of voluntary eye movements contrasts strongly with the normal latency of saccadic response to sudden target movement found in the same patients during a previous investigation. The present findings support the previously drawn conclusion that peripheral neuromuscular components of the oculomotor system are unimpeded by the disease. Comparison with observations of other authors suggests that the impairment of oculomotor performance described here may be simlar to that found in skeletal muscle systems during Parkinson's disease.