Objective To further assess oculomotor control of patients with Parkinson disease (PD) during fixation and with movement.
Design Case-control study.
Setting A Parkinson disease research, education, and clinical center.
Patients One hundred twelve patients with PD, including 18 de novo untreated patients, and 60 age-matched controls.
Intervention Modern, precise eye tracking technology was used to assess oculomotor parameters. Oculomotor function was compared between groups during fixation and while tracking a randomly displaced target on a PC monitor.
Main Outcome Measures Fixation stability and saccadic parameters.
Results All patients with PD and 2 of 60 control subjects showed oscillatory fixation instability (ocular tremor), with an average fundamental frequency of 5.7 Hz and average magnitude of 0.27°. Saccadic parameters and occurrences of square wave jerks did not differ between subjects with PD and controls. The amplitude and frequency of fixation instability did not correlate with disease duration, clinical Unified Parkinson's Disease Rating Scale scores, or dopa-equivalent dosing. No differences in oculomotor parameters were found between medicated and unmedicated patients with PD.
Conclusions All patients with PD exhibited persistent ocular tremor that prevented stability during fixation. The pervasiveness and specificity of this feature suggest that modern, precise oculomotor testing could provide a valuable early physiological biomarker for diagnosing PD.