Electromyography—A Tool in Ocular and Neurologic Diagnosis: II. Muscle Palsies

Electromyography (EMG) of the extraocular muscles has afforded insight into innervational patterns of common and uncommon diseases affecting ocular motility. The method has been described previously.1,2 The following applications are of particular interest. A. NEUROGENIC PALSIES OF EXTRAOCULAR MUSCLES 1. Third, fourth, and sixth nerve palsies are frequently encountered in ophthalmological and neurological practice. It is of diagnostic and prognostic importance to establish the site and character of the lesion. Electromyography has an important role to play in such studies. The following observations considerably amplify the findings of Bjork.3 The presence of lower motor neuron denervation may be determined. The cardinal sign of denervation is fibrillation—the minute discharge of single muscle fiber potentials which occur spontaneously without relation to volition and indicate lower motor neuron damage. Characteristic fibrillations have been noted in oculomotor palsies.1 Caution is necessary in the interpretation of ocular muscle potentials, since small, single