Botox is the trade name for botulinum toxin. In its pure form, botulinum toxin is a poisonous neurotoxic protein that is found in certain spoiled foods and causes muscle weakness. It acts as a nerve impulse blocker, preventing muscles from contracting. In an extremely dilute form, botulinum toxin has many medical applications.

Botulinum toxin is used to treat ocular conditions such as blepharospasm, an excessive contraction of the eyelid muscles that forces the eyelids closed, and hemifacial spasm, an excessive contraction of the facial muscles on one side of the face. When the toxin is injected directly into the muscles of the face or the eye, it causes the overactive muscles to relax. It usually takes a few days for the therapeutic effects to be noticeable, and the injections may need to be repeated every four to six months.

Botulinum toxin also is used to treat certain kinds of double vision. The toxin is injected directly into the eye muscle opposite the paralyzed muscle.

Botulinum toxin can also be used for cosmetic purposes to soften wrinkles around the eye. It can also weaken the brow muscles in order to diminish the deep furrows or frown lines that may appear in the middle of the forehead.

Side effects of the injections are temporary. They can include a droopy upper eyelid, double vision, and being unable to close the eyelids.

(c) 2007 The American Academy of Ophthalmology