Published online by Cambridge University Press: 05 February 2014
Primary blepharospasm is a common adult-onset focal dystonia, characterized by involuntary contractions of the periocular muscles that result in forceful eye closure and impaired opening and closing of the eyes (Marsden, 1976; Berardelli et al., 1985; Defazio et al., 2007). The severity of blepharospasm can vary from repeated frequent blinking, causing only minor discomfort, to persistent forceful closure of the eyelids leading to functional blindness (Fig. 8.1). Blepharospasm can be caused by tonic or phasic contractions of the orbicularis oculi muscles and may also be associated with levator palpebrae muscle inhibition (apraxia of eyelid opening) or involuntary movements in the lower face and masticatory muscles (Meige’s syndrome). In most cases, blepharospasm is considered primary and is only occasionally secondary to structural brain lesions or drug therapy (Jankovic, 2006).
Neurophysiological recordings of the blink reflex have given important insights into the pathophysiology of blepharospasm. In patients with blepharospasm, the recovery cycle of the R2 component of the blink reflex is enhanced, presumably owing to a lack of brainstem interneuronal inhibition (Berardelli et al., 1985, 1998). Blepharospasm is also associated with an abnormal responsiveness of the blink reflex to sensory stimuli. Studies using magnetic brain stimulation also suggest a loss of inhibition and increased plasticity in the central nervous system of patients with blepharospasm (Defazio et al., 2007; Quartarone et al., 2008).