Diagnostic Injection of Xylocaine into Extraocular Muscles ELBERT MAGOON, MD, MARC CRUCIGER, MD, ALAN B. SCOTT, MD, ARTHUR JAMPOLSKY, MD

Abstract: In situations where it is unclear which extraocular muscle is causing anomalous eye movement or to what extent one of two muscles is responsible, temporary paralysis of the muscle with Xylocaine may provide the answer. The procedure is to inject 0.2 to 0.5 cc 2% Xylocaine directly into the muscle using electromyography (EMG) for precise lo­calization, a technique similar to that of therapeutic injections of botulinum toxin (Oculinum). The procedure is especially useful for Duane's syndrome, superior oblique palsy, and other situations where abnormal muscle insertions or innervations make diagnosis ofthe muscle responsible for an eye movement anomaly difficult and surgery unpre­dictable. [Key words: botulinum toxin, eye muscle injection, Strabismus diagnosis, Xylocaine.] Ophthalmology 89:489-491, 1982

The contribution of each extraocular muscle, espe­cially for vertical and torsional movements, is not straightforward. Even between normal subjects there is some variability; in strabismus patients, these in­teractions of eye muscles may be quite unpredictable. Although good surgical results are obtained in most cases of strabismus by assuming normal muscle ac­tion, better results could be achieved if the effects of individual muscles could be quantitatively known be­fore surgery. In patients who have abnormal innerva­tion or anomalous muscle insertions, it is even more difficult to predict the effect of surgery using classic normal physiology guidelines.

Injections of 2% Xylocaine into extraocular muscles have been used in the past as a research tool to study muscle mechanics.1.2 Advanced techniques and in­strumentation developed for therapeutic injections of botulinum toxin (Oculinum)3 have made practical the diagnostic injection of Xylocaine directly into ex-

From the Smith-Kettlewell Institute of Visual Sciences, San Fran­cisco, California.

Presented at the Eighty-sixth Annual Meeting of the American Academy of Ophthalmology, Atlanta, Georgia, November 1-6, 1981.

Supported by NIH grant # EY 070271 and EY 02106 and the Smith-Kettlewell Eye Research Foundation.

Reprint requests to Elbert Magoon, MD, Smith-Kettlewell Institute of Visual Sciences, 2232 Webster Street, San Francisco, CA 94115.

traocular muscle under electromyographic control to selectively eliminate the action of possibly abnormal muscles.

This paper describes four cases where these injec­tions were found to be helpful: case 1 is Duane's syn­drome with vertical upshoot; case 2 is IV nerve palsy; case 3 is a patient with orbital anomalies; and in case 4 Xylocaine is used to predict the effect of long-term paralysis with botulinum toxin.

TECHNIQUE

Topical anesthetic drops (proparacaine) are used for anesthesia. One drop of 1% epinephrine reduces the vascularity of tissues and probably makes subcon­junctival hemorrhage less likely. A syringe of 2% Xylocaine is attached to a special electromyography (EMG) needle electrode identical to those used for therapeutic injections of Oculinum.3 This is a 26-gauge needle with an insulated wire running down the bore of the needle to provide an EMG signal. The needle is used with a small portable amplifier/speaker box that has been designed for this purpose and gives the sur­geon auditory feedback from the EMG potentials. The needle is inserted into the extraocular muscle insertion region and advanced about 15 mm along the orbital side of the muscle with the eye looking in the primary position. Then the patient is instructed to look into the

0161-6420/82/0500/0489/$00.65 © American Academy of Ophthalmology 489

OPHTHALMOLOGY • MAY 1982 • VOLUME 89 • NUMBER 5

field of action of the muscle to increase muscle activ­ity, and the needle is angled into the muscle. At this point a strong EMG signal will be heard, and the nee­dle Can be advanced 5 to 10 mm more while continuing to monitor the EMG signal. When the needle is well into the muscle, the Xylocaine can be injected. The EMG signal will gradually disappear indicating that the muscle is becoming paralyzed. With minimal effect on surrounding eye muscles, 0.2 to 0.5 cc of 2% Xylocaine usually gives effective paralysis of that muscle. Routinely a drop of chloramphenicol is given after the procedure. The whole procedure takes about five minutes. Within a few minutes the change in eye movements caused by paralysis of the injected muscle can be assessed.

CASE REPORTS

Case I-Duane's syndrome. A 16-year-old girl was referred for evaluation of Duane's syndrome , involving the left eye with upshoot on adduction. At age 3 she had a left medial rectus recession of 4.5 mm for left hypertropia and esotropia. For persistent left hypertropia she had a 3.5 mm recession of the left superior rectus and resection of the left inferior rectus 4.5 mm. After operation her hypertropia per­sisted.

Upon examination the visual acuity was 20125 right eye, 20/100 left eye. There was a 40 prism diopter left hypertropia in the primary position at distance fixation. The left eye showed very little abduction or adduction, and also demon­strated a moderate deficiency of depression. On attempted adduction of the left eye, there was significant enophthalmos and elevation. There was also a slight "A" pattern and a slight hypertropia of the left eye in all positions of gaze.

Electromyography recording from the left superior rectus showed a normal pattern of activity . Recording from the left inferior oblique showed a possible increase of some units on adduction. However, after 0.4 ml of Xylocaine reduced the EMG of this left inferior oblique to an unrecordable level, there was still no substantial alteration in the pattern of over­shoot, which proved the inferior oblique was not responsible for the overshoot. [The elevation on adduction of the left eye.] Following 0.5 cc Xylocaine into the left lateral rectus, there was a marked reduction in enophthalmos and of the vertical overshoot on adduction of the left eye, which proved co-contraction of the horizontal muscles was the cause of the overshoot.

Case 2-right superior oblique palsy. This 59-year­old woman suffered a head injury five months prior to examination. She had a 20/20 vision in both eyes. There was a right hypertropia of 12 prism diopters, with esotropia of 8 prism diopters in the primary position. In right gaze this was 7 prism diopters of right hypertropia and 4 prism diopters of esotropia; in left gaze, 12 prism diopters right hypertropia and 6 prism diopters esotropia. Forced head tilt test to the right increased the hypertropia to 16 prism diopters and to the left decreased it to 10 prism diopters . The hypertropia was also greater in downgaze and less in upgaze. Cyclotor­sion measured with a Hess screen in primary position was 10" excyclotorsion, decreasing to 2° in upgaze and increasing to 20" in downgaze. (Table I).

The effect of right inferior oblique weakening on heF'tor­sional diplopia was examined by the injection of 0.5 cc 2%

490

Table 1. Case 2-Right Superior Oblique Palsy (Hess Screen Torsion Measurements)

Gaze Before After Xylocaine After Positions Treatment Paralysis of RIO Surgery

30° up 2° excyclo 5° incyclo 5° incyclo 15° up 5° excyclo 3° incyclo 2° incyclo Straight

ahead 10° excyclo 2° excyclo No torsion 15° down 15° excyclo 5° excyclo 3° excyclo 300 down 20° excyclo 10° excyclo 10° excyclo

Xylocaine into the right inferior oblique muscle. Two min­utes after injection, her torsional diplopia was alleviated in the primary position, where there was only 2° excyclotor­sion. In upgaze there was now 5° of incyclotorsion, and in downgaze there was 10° excyclotorsion; vertical and hori­zontal deviations were unchanged.

It could be predicted that surgical correction of the tor­sional diplopia could be achieved with a right inferior oblique weakening procedure but that additional vertical and hori­zontal procedures would be necessary to correct the ocular misalignments in all fields of gaze.

The right inferior oblique muscle was recessed to a posi­tion II mm from the limbus and 2 - 3 mm lateral to the in­ferior rectus muscle. The right medial rectus muscle was subjected to tenotomy of the upper 9/10 of its insertion (as an alternative to 3-4 mm infraplacement). The left inferior rec­tus was recessed 4.5 mm on an adjustable suture that was tightened 2 mm the next day to effect a 2.5 mm recession. This procedure resulted in orthophoria in primary gaze and gaze to either side, with 2 prism diopters right hypertropia in downgaze. Cyclotorsion was improved. There was no tor­sion in the primary position. In downgaze it was now only 10" excyclotorsion and in upgaze 5° in cyclotorsion (Table O.

Case 3-right hypotropia with orbital anomaly. This 44-year-old woman had suffered sinusitis in infancy that resulted in right facial hypoplasia of the inferior orbit and maxilla. Recently, her large, right hypophoria had become a tropia, giving her diplopia and headaches. She had 20/20 vi­sion in each eye. There was a 25 prism diopter right hypo­tropia that decreased in right gaze to 20 prism diopters . Forced head tilt to the right decreased the deviation to 20 prism diopters and tilt to the left increased the deviation to 35 prism diopters right hypotropia . Forced duction test re­vealed that the right eye was very slightly limited to eleva­tion .

To assess the effect of possible right inferior rectus muscle weakening procedure, this muscle was injected with 5 cc Xylocaine. In this case inferior rectus muscle vertical effect was exceptionally noncomitant and was confined to right­gaze and downgaze. Before injection the eye depressed fully in all fields of gaze. After the injection the eye could depress fully in adduction but not in rightgaze and downgaze. Up­gaze was minimally affected, as was left gaze. In the primary position, there remained a 10 prism diopter right hypotropia, although in straight downgaze there was a 15 prism diopter right hypertropia created by the injection. It was judged that a further procedure to affect upgaze and left gaze was re­quired. At surgery, the right inferior rectus and left superior rectus were each recessed 4 mm on an adjustable suture; no subsequent adjustment was necessary. After operation there was a 2 prism diopter right hypotropia in primary, right, and left gaze. There was no deviation upgaze or downgaze.

MAGOON, et al • XYLOCAINE INJECTION

Case 4-sixth nerve innervational anomaly. A 20-year-old woman had undergone successful surgery for a brain tumor. There was, however, left sixth nerve damage resulting in almost total paralysis. Over one year after her neurosurgery, the left medial rectus muscle was recessed 8 or 9 mm and the left lateral rectus resected 7 or 8 mm. This resulted in good mobility of the left eye and satisfactory alignment much of the time.

However, after gazing to the left, the left eye would not be able to return to primary position. This caused diplopia and exotropia that was quite distressing to the patient. This anomaly was studied extensively with EMG and found to be an innervational anomaly (neuromyotonia) of the lateral rec­tus muscle. That is, some left lateral rectus muscle motor units were unable to be appropriately inhibited. Carbama­zepine (Tegretol) treatment was not tolerated. An injec­tion of Xylocaine weakened the lateral rectus muscle suf­ficiently to prevent the patient's distressing symptoms. Semi-annual injection of Botulinum toxin (Oculinum) has been a successful treatment for over three years.

DISCUSSION

Analysis using normal muscle physiology is usually sufficient to guide surgery. However, in cases of ab­normal innervations, muscle insertions and mechan­ics, it may be helpful to be certain exactly what are the effects of certain muscles. In these situations diagnostic injection of Xylocaine may be helpful.

Case 1 is a typical Duane's co-contraction up­shoot.4,5 With Xylocaine injection, one can be certain the inferior oblique plays no role in the upshoot on adduction, and that it is caused solely by co­contraction of medial and lateral rectus muscles. EMG alone can determine horizontal rectus muscle co­contraction and can demonstrate the patterns of mus­cle recruitment; but temporary paralysis is the only preoperative way to determine quantitatively which muscles are causing the upshoot. Surgery can be guided by this knowledge.

A positive forced duction test in Duane's syndrome always presents a problem. One does not know how much force is contributed by active anomalous inner­vation to the lateral rectus, and how much is contrib­uted by passive stretch of a fibrotic muscle. Xylocaine injection can eliminate the active innervational com­ponent and enable one to perform a truly passive forced duction test.

Case 2 is an example of torsional diplopia where Xylocaine injection helps the surgeon predict whether simple weakening of the inferior oblique muscle (as by a Z-lengthening procedure) will cure the torsional problem. Also, it helps predict the need for additional vertical muscle surgery to correct the vertical devia­tion.

The inferior rectus muscle has been injected to pre­dict the effect of inferior rectus recession on the vari­ous fields of gaze as in case 3. Since the division of labor between vertical muscles in various fields of gaze varies from patient to patient, injection helps predict effects of surgery.

Case 4 illustrates the use of Xylocaine injection to predict whether long-term abolition of innervation will be effective therapeutically. In addition to Duane's syndrome, IV nerve palsy, and orbital anomalies, the technique has been found to be helpful in cases of III nerve anomalous regeneration, partial VI nerve palsy, and possible anomalous muscle insertions. The tech­nique may not be of value for routine horizontal strabismus, but it has been found helpful for situations where division of labor between individual muscles is uncertain.

By causing temporary paralysis, Xylocaine injec­tions help assess the active force of innervated muscle, but not passive stretch forces. This helps predict the effect of a surgical weakening procedure in the field of action of the muscle. But a few minutes of paralysis will not remove passive stretch forces and will not predict the effects of recession of a tight muscle in gaze positions out of the field of its action.

No complications except for small subconjunctival hemorrhage have been encountered. By force mea­surements at least 90% of muscle strength can be temporarily eliminated with Xylocaine. The precise localization of the drug is critical to this purpose. The technique requires a thorough knowledge of eye mus­cle mechanics and innervational patterns seen by electromyography. Since the techniques and EMG ap­paratus for diagnostic Xylocaine injection are the same as those recently developed for the therapeutic injec­tion of botulinum toxin (Oculinum), they are readily available to interested ophthalmologists.

REFERENCES

1. Scott AB, Collins CC, O'Meara DM, Zipf RF. Contribution of individual extraocular muscles to eye movement. ARVO Abstracts. Invest Ophthalmol 1973; 63.

2. Tamler E, Jampolsky A, Marg E. Electromyography in strabis­mus. Califomia Med 1959; 90:437-9

3. Scott AB. B'otulinum toxin injection into extraocular muscles as an alternative to strabismus surgery. Ophthalmology 1980; 87:1044-9.

4. Scott AB. Upshoots and downshoots. In: Souza-Dias C ed. V Congress of the CLADE (Conselho Latino-Americano de Es­trabismo), October 16-17, 1976, Guaruja-Brasil. Sao Paulo: Oficinas das Edicoes Loyola, 1978.

5. Scott AB, Wong GY. Duane's syndrome: an electromyographic study. Arch Ophthalmol 1972; 87:140-7.

491