Photic Blink Reflex in People With Blepharospasm and Increased Blinking

Objective: * The purpose of the first study of this protocol is to improve understanding of the role played by light sensitivity in the pathophysiology of blepharospasm (BPS). * As a characteristic feature of BPS, the electrocutaneous blink reflex recovery cycle (EBR rc) shows an increased recovery index of R2 compared with healthy subjects. * In the first study proposed under this protocol we will study the recovery cycle of the blink reflex evoked by a light stimulus (PBR rc) and the effect of a light stimulus on the EBR (MBR rc) in patient with BPS. Since photophobia and increased blinking are common symptoms in this group of patients, we will look for possible correlations between neurophysiological data and the Light Sensitivity Questionnaire (LSQ) or the Blink rate (Brt). The second study proposed under this protocol will explore the PBR rc and the MBR rc in patients with increased blinking alone, a condition indicated as a possible precursor of BPS. Study population: We plan to recruit 24 patients with blepharospasm, 24 healthy volunteers (HVs) and 24 patients with increased blinking alone. Design: In two different studies, we will compare all the results from the EBR rc, PBR rc and MBR rc between BPS patients (first study) or increased blinking patients (second study) and HVs. We will also look for possible correlation between the neurophysiologic data and the clinical scales acquired during a clinical assessment. In the EBR rc procedure, the supraorbital nerve will be stimulated with paired electrical stimuli at varying ISIs and the EMG response from the orbicularis oculi muscles will be recorded. In the PBR rc procedure, paired light stimuli will be given at varying interstimulus intervals (ISIs) and the EMG responses from the orbicularis oculi will be recorded. In the MBR rc study a weak light stimulation will be given at varying ISIs before an electrical stimulation of the supraorbital nerve. Each experimental procedure will last about 1 hour. There will be one screening visit and up to 4 testing visits per participant. However, participant can either undergo all the experimental procedures or participate in only some of them and will be allowed to participate in two experimental procedures per testing visit. Outcome measurements: * EBR rc, PBR rc, MBR rc: the electromyography (EMG) responses at different interstimulus intervals (ISIs). * Blink rate: number of eye blinks per minute. * LQs: the total score of the Light Questionnaire Scale. These results will be compared between the two patient groups and HVs. We will look for possible correlations between neurophysiological and clinical data.