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Fixational microsaccades: A quantitative and objective measure of disability in multiple sclerosis

Background: Objective tools for prognosis and disease progression monitoring in multiple sclerosis (MS) are lacking. The visuomotor system could be used to track motor dysfunction at the micron scale through the monitoring of fixational microsaccades. Aims: The aim of this study was to evaluate whether microsaccades are correlated with standard MS disability metrics and to assess whether these methods play a predictive role in MS disability. Method: We used a custom-built retinal eye tracker, the tracking scanning laser ophthalmoscope (TSLO), to record fixation in 111 participants with MS and 100 unaffected controls. Results: In MS participants, a greater number of microsaccades showed significant association with higher Expanded Disability Status Scale score (EDSS, p < 0.001), nine-hole peg test (non-dominant: p = 0.006), Symbol Digit Modalities Test (SMDT, p = 0.014), and Functional Systems Scores (FSS) including brainstem (p = 0.005), cerebellar (p = 0.011), and pyramidal (p = 0.009). Both brainstem FSS and patient-reported fatigue showed significant associations with microsaccade number, amplitude, and peak acceleration. Participants with MS showed a statistically different average number (p = 0.020), peak vertical acceleration (p = 0.003), and vertical amplitude (p < 0.001) versus controls. Logistic regression models for MS disability were created using TSLO microsaccade metrics and paraclinical tests with ⩾80% accuracy. Conclusion: Microsaccades provide objective measurements of MS disability level and disease worsening.