Ocular Fixation: A Useful Aid in the Differential Diagnosis of Parkinsonism?

Eye movements occurring during ocular fixation have been recorded in normal, idiopathic Parkinson's (IPD) and atypical Parkinson's (AP) subject groups using an infrared limbus eye tracker. All subjects displayed periods of ocular fixation interspaced by saccadic intrusions. The saccadic intrusion amplitude and frequency displayed an increase in value in both the IPD and AP groups relative to those values obtained for the control group. The total time spent fixating displayed a reduction in value in both the IPD and AP groups relative to that observed for the normal control group. The mean fixation displacement was increased in both the IPD and AP groups relative to that observed for the normal control subject group. Analysis of ocular fixation has the potential to provide a simple non-invasive quantitative and objective method that will aid the differential diagnosis of parkinsonism.