Using precise eye-tracking technology, researchers found ocular fixation instability in all 112 patients (mean age of 66) with Parkinson’s disease (PD) compared with only 2 of 60 healthy age-matched controls. Precise oculomotor testing could provide clinicians with a simple means to accurately diagnose PD with accuracy well exceeding that of clinical assessments. The patients have had PD symptoms for an average of 5.5 years.
The investigators report that while fixating on a randomly displaced target on a computer screen, all 112 patients with PD showed persistent instability characterized by oscillatory behavior. In contrast, 58 of 60 controls showed highly stable fixations characterized by minimal drift of gaze and no oscillatory behavior.
The mean amplitude of the fixation instability was 0.27 degrees horizontally and 0.33 degrees vertically, ranging from 0.14 to 1.63 degrees (vertical component of the instability was of greater magnitude). In 71 patients (63.3%), the maximum amplitude of the instability at times reached the 0.5-degree threshold for obscuring foveal vision.