Electromyographic Study of Conditions involving Limited Mobility of the Eye, chiefly due to Neurogenic Pareses

ELECTROMYOGRAPHY has supplied us with information of great importance in the understanding of the physiology of the muscular system under normal and diseased conditions.Electromyography (EMG) has also become a routine clinical method that is widely used in diagnosis, particularly ofpareses.Not until quite recently was a method devised of obtaining electromyo- graphic recordings from the extrinsic muscles of the human eye (Bj6rk, 1952; Bjork and Kugelberg, 1953a).Certain conditions characteristic of the ocular muscles were thereby demonstrated.Thus the action potentials are smaller than in other human muscles (duration 1 60 ±0 06 milliseconds in the recti).They attain far higher frequencies and recruitment is more rapid than in other muscles (Bjork and Kugelberg, 1953a).It was further shown that, when the eye is in the primary position, all the recti muscles and the levator palpebrae superioris manifest a considerable activity.In simultaneous recording from the internal and external recti it has been shown that, on outward gaze, the activity in the agonist increases greatly, while it falls successively in the antagonist but does not usually disappear even in the extreme outward position (Bj6rk and Kugelberg, 1953b).A preliminary account of electromyographic studies of paretic eye muscles has been published earlier (Bj6rk, 1952).In the present paper a more detailed report will be given of investigations into cases of paresis due to a lesion of the peripheral motor neuron.Some cases have also been included in which such a lesion has been questioned without a distinct diagnosis being possible by the methods used hitherto.Neurogenic pareses in other muscles have been studied by many authors, and the myographic picture has therefore already been thoroughly analysed.In lesions of anterior horn cells or motor nerve fibres there is a falling off in the number of action potentials which is largely proportional to the number of nerve fibres that have been put out of function and also to the diminution in muscular force (Lindsley, 1935;Seyffarth, 1938Seyffarth, , 1940)).If the lesion is so severe that nerve fibres degenerate, fibrillations occur after 2 to 3 weeks (Denny-Brown and Pennybacker, 1938; Weddell and others, 1944).They consist of small potentials of 1-2 m.sec.duration with an