Predictive ocular motor control in Parkinson's disease.
A comparison was made of predictive eye movements of both the saccadic and pursuit ocular motor systems in parkinsonian patients and aged-matched normal controls. In a predictive task our patients, who were mildly or moderately affected, showed a reduced tendency to make anticipatory saccades compared with normal controls. Although there was some impairment of pursuit during a nonpredictive task as shown by an increased phase lag, a normal amount of improvement took place with a predictive task. This difference between prediction in the saccadic and pursuit system is possibly explained by an increased reliance on a visual input by parkinsonian patients which prevents them making use of verbal instruction to generate anticipatory (eye in advance of target) saccades. Improvement of pursuit with a predictive target track is possible in such patients since normally in these circumstances the target is mainly followed rather than anticipated. The metrics of saccadic and smooth pursuit eye movements (saccadic velocity and pursuit turnover velocity) were normal.