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Electromyography of skeletal muscles has been utilized as a diagnostic technique in the field of neurology for over 20 years. It was first adapted successfully about seven years ago to the study of extraocular muscles. Its main contribution has been in helping to localize the site of a lesion which produced muscle weakness, i.e., whether the lesion was primarily in the motor nerve to the muscle (neurogenic), at the neuromuscular junction (e.g., myasthenia gravis), or in the muscle itself (myopathic).
The principle of the examination is as follows: A needle electrode inserted into a muscle will pick up the electrical activity produced by those few muscle fibers located close to the tip of the needle. This electrical activity is amplified electronically and is seen as a deflection of the baseline up and down on a screen which is basically the same as a TV-screen. In a normal relaxed muscle, no
Electromyography. Arch Ophthalmol. 1960;64(5):650-652. doi:10.1001/archopht.1960.01840010652003