MOTOR PERSISTENCE OF ORBICULARIS OCULI MUSCLE IN EYELID-OPENING DISORDERS

We describe clinical and EMG findings in three patients with an inability to reopen the eyes after voluntary closure of the eyelids. Synchronous EMG recording from the levator palpebrae (LP) and orbicularis oculi (OrbOc) muscles revealed that after voluntary closure of the eyelids and upon the command to open the eyes, all three patients were unable to inhibit the ''voluntary'' contraction of the OrbOc muscles, while on clinical examination there was no evidence of ongoing OrbOc muscle contraction. This ''motor persistence'' was restricted predominantly to the pretarsal portion of the OrbOc. In one patient, it occurred as an isolated abnormality of the eyelid movement and was recorded as an additional EMG abnormality in two patients with blepharospasm and involuntary LP inhibition. Clinical examination alone cannot differentiate this type of disorder of supranuclear control of eyelid movement from involuntary LP inhibition; simultaneous EMG recording from the LP and OrbOc muscles is required. Injection of botulinum toxin into the pretarsal portion of OrbOc muscles is helpful.