Fixational Microsaccades in Patients With Parkinson Disease

Background: Fixational microsaccades (FM) encompass the involuntary, small-scale movements of the eye that occur as we attempt to fixate on a single point. These movements are crucial for maintaining a steady visual perception despite our gaze's constant, subtle changes. FM is significant because it can serve as an indicator of central nervous system disorders; for example, altered FM correlated with multiple sclerosis disability levels and disease progression. This study aims to characterize FM in patients with Parkinson disease (PD). Methods: Fourteen older adults (age 71.0 ± 7.2 years, 6 females) with PD and 17 controls (age 73.4 ± 4.4 years, 15 females) were recruited. Retinal motion traces were recorded using a tracking scanning laser ophthalmoscope (TSLO, RetiTrack, C. Light Technologies, Cambridge, MA). The number of FM, saccade amplitude, velocity, peak velocity, and frequency were measured. Results: All FM measurements were significantly different between PD and controls ( P values < 0.05): the number of saccades (19.45 ± 7.40 vs 10.19 ± 6.69, P = 0.001), average amplitude (0.44 ± 0.15 vs 0.33 ± 0.10°, P = 0.027), average velocity (7.45 ± 1.44 vs 6.46 ± 0.96°/s, P = 0.037), average peak velocity (10.48 ± 2.99 vs 8.49 ± 2.03°/s, P = 0.044), and saccade frequency (1.95 ± 0.74 vs 1.07 ± 0.69 Hz, P = 0.002). Furthermore, the average amplitude strongly correlated with the Movement Disorders Society-sponsored Unified Parkinson Disease Rating Scale part III (MDS UPDRS III) motor subscale (r = 0.62, P = 0.02) and the Unified Parkinson Disease Rating Scale Hoehn and Yahr Stage (UPDRS HY Stage) (r = 0.62, P = 0.02). Similarly, average velocity and average peak velocity significantly correlated with both UPDRS III (r = 0.56, P = 0.04) and UPDRS HY Stage (r = 0.59, P = 0.03–0.04). These results indicated that PD patients had larger, more frequent, and quicker microsaccades, which were associated with disease severity. Conclusions: To our knowledge, this is the first study to characterize FM using TSLO in patients with PD. The tracking scanning laser ophthalmoscope appears to have high precision and sensitivity, offering detailed, real-time retinal imaging with minimal motion artifact. The results indicate that impaired fixational microsaccades in PD correlate with disease severity, suggesting that altered FM could serve as a biomarker for progression and treatment response.