A novel eye-tracking oculomotor score correlates with excessive daytime sleepiness and motor progression in Parkinson’s disease

Parkinson’s disease (PD) progression involves complex interactions between motor and non-motor systems. Oculomotor (OCM) deficits are a known feature, but current eye-tracking metrics are often fragmented. Excessive daytime sleepiness (EDS) is a prevalent non-motor symptom, yet its relationship with OCM function remains unexplored. Therefore, this study developed a novel global OCM score as a potential sensitive correlate of PD severity and to investigate its association with EDS. In this cross-sectional study, the OCM score integrated saccadic and gaze stability metrics. Participants - PD patients ( n = 44, Hoehn & Yahr stages 1–3) and age-matched controls ( n = 21) - underwent assessment with the Epworth Sleepiness Scale (ESS) and motor scales during ON-medication states. Strong interocular consistency was found, but PD patients showed significantly lower OCM scores versus controls. Scores showed severity-dependent deterioration: 92% of controls maintained scores ≥ 50, versus only 26% of PD patients, while 40% of PD patients scored < 50. A strong negative correlation existed with H&Y-M stage ( r =-0.66; P < 0.0001). Paradoxically, a positive significant correlation ( r = 0.28; P = 0.02) was found between OCM scores and ESS in PD (higher scores with greater sleepiness), a relationship absent in controls. The OCM score shows promise as a potential indicator of motor impairment and warrants further investigation in longitudinal studies. Its association with EDS suggests a complex interaction between sleep-wake and OCM systems, potentially mediated by sleep deprivation-induced dopaminergic dysfunction. This score holds promise for objective monitoring, patient stratification, and elucidating motor/non-motor interplay in PD.