Revisiting eye blink in Parkinson's disease.

Spontaneous blinking is a rapid and unconscious type of blinking that has been linked to several cognitive processes. Blink rate has been established as a reliable measure of cognitive processing and a predictor of dopamine-related cognitive function. Patients with Parkinson's disease (PD) have a reduced spontaneous blink rate. In this study, we propose an additional measure of blink characteristic, namely blink duration, and evaluate its alteration in a large cohort of 107 patients with PD. We also investigate the relationship between blink rate and blink duration and disease characteristics such as severity and dopaminergic neuronal loss. The results show that the blink rate is reduced, and blink duration is increased in patients compared to healthy controls. Blink rate is related to motor deficit severity and significantly correlated with dopamine depletion (dopamine transporter striatal binding ratio). Conversely, blink duration is related to non-motor aspects such as sleepiness. These findings highlight the potential of blink as a distinguishing feature of Parkinson's disease, underscoring the importance of incorporating blink assessments into standardized oculomotor testing protocols for PD.