Blepharospasm is the condition in which there is involuntary closing of the eyelids due to sustained, forced dystonic contraction of orbicularis oculi (OO) muscle. So called apraxia of lid opening (ALO) is another condition of involuntary eyelid closure which is suspected to be originated from the involuntary levator palpebrae (LP) inhibition. Clinically it is difficult to differentiate blepharospasm and ALO, and these two conditions are sometimes associated. This fact makes it difficult to predict and evaluate Botulinum A toxin injection treatment outcome. These disorders of involuntary eyelid closure are thought to have disturbed normal antagonistic activities of OO and LP, so electrophysiologic evaluation using synchronous EMG recording of LP and OO helps understanding the antagonistic activities of these two muscles and the origin of varying forms of eyelid movement disorders, and analysing the cause of unsatisfactory response to the Botulinum A toxin treatment.
