Pervasive Ocular Tremor in Patients With Parkinson Disease

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 degrees. 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.