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   Table of Contents      
ARTICLES
Year : 1973  |  Volume : 21  |  Issue : 1  |  Page : 1-4

Electromyography of extraocular muscles (EOM)


1 Dept of Ophthalmology, King Edward Memorial Hospital, Bombay -12, India
2 Laboratory of Electrophysiology, Gordhandas Sunderdas Medical College, Bombay-12, India

Correspondence Address:
R C Patel
Dept of Ophthalmology, King Edward Memorial Hospital, Bombay -12
India
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Source of Support: None, Conflict of Interest: None


PMID: 4792999

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How to cite this article:
Patel R C, Shahani M. Electromyography of extraocular muscles (EOM). Indian J Ophthalmol 1973;21:1-4

How to cite this URL:
Patel R C, Shahani M. Electromyography of extraocular muscles (EOM). Indian J Ophthalmol [serial online] 1973 [cited 2020 Dec 3];21:1-4. Available from: https://www.ijo.in/text.asp?1973/21/1/1/31427


  Introduction Top


The electrophysiological studies in eye muscles can be based widely on knowledge of the electrical behaviour of peripheral skeletal muscles.

DUBOIS-REYMOND in 1848, estab­lished the `action current' principle or wave of the electrical negativity of the nerve impulse.

PIPER in 1907, obtained first re­corded electromyogram.

ADRIAN AND BRONK in 1929 intro­duced concentric needle electrodes which made it possible to pick up po­tentials developed by a single motor unit.

As early as 1930, COOPER AND ECCLES studied the mechanical and electrical response of medial rectus muscle to tetanic stimulation.

With respect to extraocular muscles pioneering work was done by SHER­RINGTON on reciprocal innervation and HERRING on equal distribution of nerve impulse between contralateral synergists. The outstanding papers of BJORK AND KUGELBERG have pre­sented the first detailed study of elec­tromyography of extraocular muscles in man.

BREININ [1] and his colleagues have studied various aspects of electromyo­graphy of extraocular muscles like electromyography of normal extra­ocular muscles, EMG of extraocular muscles in conditions of limited mo­bility chiefly due to neurogenic para­lysis, as a tool in neurogenic diagno­sis.

TAMLER, MERG AND JAMPOLSKY [8] studied electromyography of co-acti­vity of human extraocular muscles in following movements, in saccadic eye movements and following movements of the eye between tertiary positions.

The recording of potentials from the extraocular muscles in man is a technique which may provide a grea­ter insight in understanding their func­tion.


  Material and Method Top


Normal subjects, 13 males and 2 females between the ages of 20-70 years were chosen from patients at­tending out-patient department of K.E.M. Hospital, Bombay. They had no clinical manifestations of the in­volvement of extraocular muscles. Electromyography was carried out with concentric bipolar needle electro­des using Medelec MS-4 EMG ma­chine.

Conjunctiva was anaesthetised with anaethaine 0.5% at intervals of five minutes. An eye speculum was put. A concentric needle electrode 25 to 50 mm. long and a diameter of 0.45 mm. made of platinum lead and insulated from steel cannula was used.

Autoclaved electrode was ,inserted through the conjunctiva into the belly of the muscle almost parallel to the muscle axis. A burst of impulses and a high crescendo sound in loud spea­ker indicates the proper placement of the electrode.

Electrical activity from the muscle is picked up by electrode and led off by means of shielded wires to a box type pre-amplifier connected to the machine.

The visual display of the electrical activity was made by cathode ray oscil­loscope. Recordings were made pho­tographically by 35 mm. still camera. Tracings can be suitably displayed by adjusting the sweep speed.

The electrical activity of the mus­cle was made audible by a loud spea­ker.

Recordings of electrical activity were made in primary position of the eyes, in the direction of the action of the muscle and the direction opposite to the action of the muscle. Electri­cal activity was studied mainly in late­ral and medial recti in normal sub­jects.

Observations

As soon as the electrode was in­troduced in the muscle, the electrical activity was noted on the oscilloscope screen as well as by sharpness of sound in the loud speaker. The degree of activity recorded was dependant upon the correct site of the electrode tip in the muscle.

With the eyes in primary position and the electrode inserted in the mus­cle, continuous electrical activity was noted in all the subjects. Out of 15 cases, 3 cases showed lateral rectus (LR) and 2 cases medial rectus (MR) interference pattern. The range of amplitude noted was 25-149μv in case of LR and 17-125 μv in case of MR during rest. [Figure - 2]

When the eyes were moved in the direction of the action of the muscle, there was distinct increase in the am­plitude, and pattern of the electrical activity from single oscillation or mix­ed pattern became a complex pattern of interference in all cases. [Figure - 1] The pitch of the electromyographic sound as noted from the loud speaker rose to sharp crescendo into sharp loud sound like a fast moving train in all cases. The amplitudes noted ranged from 33-958μv and 58-917 µv in cases of LR and MR respectively during the action of the muscles. The frequency noted was very fast, several hundreds sec.

Electrical activity of the muscle during the position of the eyes in the direction opposite to cardinal action of the muscle were found to be mar­kedly inhibited. In two cases in LR no activity was noted while in all other cases single discrete potentials were noted. The duration in LR and MR ranged from 1.6 to 2.5 m sec. and 2.5 to 3.3 m sec. respectively. The ampli­tude ranged from 12.5 to 125 μv in LR and 50 to 125 µv in MR. [Figure - 3]

Low amplitude values were noted in old patients (60 years and above) both in MR - and LR while higher am­plitude values were noted in those be­low 40 years.


  Discussion Top


A striking characteristic of extra­ocular muscle is continuous electrical activity during resting state in pri­mary position, as against no electrical activity in other skeletal muscles at rest. [Figure - 2]

The electrode in an extraocular muscle may record from a single unit (motor unit) which is recognised by its rhythmicity and constant size and shape. When a single unit responds a pattern of single oscillations in the form of spikes is observed.

If several units are being recorded, they will appear as separate impulses unless two or more happen to fall synchronously. In this case they will summate or show the total of their individual amplitudes. Here the res­ponse is so great that the individual units cover one another so that they cannot be individually resolved, and one gets an interference pattern. This summated pattern will show notches or humps where motor units have their maxima or minima. This pattern in extraocular muscle is seen common­ly when the muscle is contracting.

When more than one unit is res­ponding but still the response is not so great so that individual units can­not be masked, the picture is called mixed pattern.

The change from simple pattern to interference pattern [Figure - 1] is due to

(1) Increase in frequency of dis­charge of motor units.

(2) Recruitment of additional mo­tor units which may be of lar­ger amplitude.

Electrically there is no position of rest; the so called position of rest of extraocular muscles, the straight ahead position of the eyes involves constant contraction of number of motor units in all the muscles.

Sherrington in his epic work en­unciated the law of reciprocal inner­vatic-ti. This is confirmed by electro­myography of the antagonist muscles. In all cases we noticed that there was marked diminution of electrical activity, when the eyes were made to look in the direction opposite to that of the action of that particular muscle. In two cases there was no electrical acti­vity, while in the remaining cases dis­crete single potentials were noted. The amplitude ranged from 12 to 150 µv, while the duration ranged from 1.6 to 3.3 m sec. Frequency ranged from 19 to 61 /sec. [Figure - 3]

The motor unit of ocular muscle is much smaller than that of the skele­tal muscle as evidenced by small dis­crete amplitudes in the electromyo­graph of the antagonist muscle. The small duration of these potentials may be due to smaller fibre diameter of the ocular muscle (15.9 to 22.7 μv) than that of the other striated muscles.

In summarising it may be said that electrical activity in the ocular mus­cle differs in some respects from that in skeletal muscles. The ocular mo­tor unit has a lower amplitude and shorter duration. The frequency is much higher. The individual motor units can recruit faster than the ske­letal motor units. There is constant electrical activity in the so called posi­tion of rest in extraocular muscles while skeletal muscles are electrically silent in position of rest. [Table 1]


  Summary and Conclusions Top


Electromyography was done in 15 normal volunteers.

Electromyography of extraocular muscles in man is clinically feasible, relatively simple and without ill ef­fects. It provides important tool for physiological study of innervational factors of extraocular muscles.

Electromyography of extraocular muscles show that motor unit is sim­pler, and smaller than skeletal mus­cles, shorter in duration and can fire at a greater frequency.

There is no position of innervation­al rest. Reciprocal innervation in vergences and versions is exhibited by gradual decrement of the antagonists and augmentation of agonists. The field of action of a muscle can be readily demonstrated[9].

 
  References Top

1.
Breinin, G. M. and Moidaver J.: Electromyography of human extra­ocular muscles. Arch. Oph. 54: 206, 1955.  Back to cited text no. 1
    
2.
Hughes. W. F.: EMG of Eye Muscles Year Book of Ophthalmo­logy, 1963-64, p. 66.  Back to cited text no. 2
    
3.
Jampolsky, A., Tamler and Merg: Artefacts and normal variations in human EMG. Arch. Oph. (Chi­cago) 61: 402, 1959.  Back to cited text no. 3
    
4.
Licht, S.: Electrodiagnosis and Electromyography. Elizabeth Licht Publications, 1956.  Back to cited text no. 4
    
5.
Merg, E. et al.: Elements of hu­man extraocular muscle electromyo­graphy. Arch. Oph. (Chicago) 61: 258, 1959.  Back to cited text no. 5
    
6.
Miller, J. E.: The EMG of Ver­gence movement. Arch. Oph. (Chicago) 62: 790, 1959.  Back to cited text no. 6
    
7.
Moses, R. A.: Adler's Physiology of the Eye. 5th Edition, The C. V. Mosby Company.  Back to cited text no. 7
    
8.
Tamler, E., Merg, E. and Jampolsky, A. et al.: EMG of human saccadic eye movements. Arch. Oph. (Chicago) 62: 657, 1959.  Back to cited text no. 8
    
9.
Tamler, E. and Jampolsky, A. et al.: EMG study of following mo­vements of the eye between tertiary positions. Arch. Oph. (Chicago) 62: 804, 1959.  Back to cited text no. 9
    


    Figures

  [Figure - 1], [Figure - 2], [Figure - 3]



 

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Introduction
Material and Method
Discussion
Summary and Conc...
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