Facial spastic disorders are neurologic conditions characterized by involuntary, forceful contraction of facial muscles. When the muscles affected include eyelid muscles, uncontrollable closure of the eyelids can occur, resulting in functional vision impairment or even functional blindness.
People who have these disorders are often forced to alter their lives to minimize the spasm. Due to the associated symptoms (light sensitivity and eye irritation), people are often misdiagnosed as having dry eye syndrome and treated as such for years before the correct diagnosis is made. This can be an intensely frustrating and disheartening experience.
Benign essential blepharospasm is a focal dystonia typically limited to the muscles of the eyelids (orbicularis oculi). It tends to affect both eyes, though may not be symmetric. It can spread to involve other facial muscles (oromandibular dystonia or Meige syndrome) or even other parts of the body. Both tend to improve or resolve during sleep.
Hemifacial spasm is not a true dystonia. It is due to irritation of the facial nerve, most commonly by a nearby blood vessel next to the brain. It tends to affect only one side of the face and may or may not involve the eyelid muscles. It tends to continue even during sleep.
In most circumstances, all three of these conditions can be effectively managed with the injection of botulinum toxin into the affected muscles to lessen or stop the spasms, while maintaining reasonable muscle strength for their main functions. This must be repeated in regular intervals, which can vary from person to person.
Another site from which to gain valuable information is the Benign Essential Blepharospasm Research Foundation.