Spectral analysis of electromyograms for extraocular muscles in normal and ophthalmoplegia cases.

Quantitative analysis of electromyograms (EMGs) of the extraocular muscles (EOMs), which contain fast fibers, like all skeletal muscles, but also slow fibers, was carried out in healthy subjects and a patient with external ophthalmoplegia. Interference EMGs of normal extraocular muscles demonstrated a relatively higher power spectrum in the higher frequency domain than those of the biceps brachii (BB). In the case of ophthalmoplegia, the lateral rectus (LR) and medial rectus (MR) muscles demonstrated a power spectrum with a wide ranging distribution up to 2,000 Hz in the early stage of recovery. Conservative treatment led to an improvement in the patient's ocular motility accompanied by a gradual shift of the spectrum towards lower frequencies within 265 days, during which time EMG examinations were performed four times. The results imply that the electrical activity of the slow fibers proper in the extraocular muscles affects the high frequency domain of the power spectrum and that the those fibers synchronously improve with fast fibers.