[Spectral analysis of electromyograms in the strabismus cases--before and after botulinum toxin injection].

An examination was made on the mechanism of botulinum toxin injection into extraocular muscles with the use of the power spectrum. Four cases of esotropia (11-16 years) were treated with 0.5 to 3.25 units of botulinum toxin injected into the medical rectus muscle. After the injection, power spectral components under 300 Hz were decreased. In the case of repeated injections, the spectrum resembled the pattern of slow fiber components. It is assumed that a malfunction of fast fibers rather than slow ones is related to the effects of botulinum toxin on extraocular muscles.