Alan B. Scott

Botulinum Toxin Injection into Extraocular Muscles as an Alternative to Strabismus Surgery

Sixty-seven injections of botulinum. A toxin were given to patients for correction of strabismus. No systemic complications of any kind have occurred. The maximum time of paralysis occurs four to five days following the injection, and then gradually diminishes, depending on the dose. The maximum correction of strabismus has been 40 prism diopters. The maximum follow-up following injection is six months. Injection of botulinum A toxin into extraocular muscle to weaken the muscle appears to be a practical adjunct or alternative to surgical correction.

Botulinum Toxin Injection in the Management of Lateral Rectus Paresis

Seventeen patients with lateral rectus paresis (3 bilateral) were treated by injection of botulinum toxin to the antagonist medial rectus to eliminate its unopposed action or to eliminate its contracture. This allowed maintenance of single binocular vision in most patients while waiting for the palsy to heal, especially important in two children. It allowed avoidance of surgery in some cases, and a reduction or elimination of medial rectus surgery when later intervention was needed for persistent paralysis. The release of medial rectus shortening and stiffness (contracture) after just a few days of denervation was unexpected. This implies an internal muscular mechanism of contracture, perhaps sarcomere overlap, different from the fibrotic changes found in muscles after inflammation or trauma. These results also provide a rationale for experimental denervation treatment of contracture in limb muscle disorders.

Botulinum Treatment of Childhood Strabismus

Four hundred thirteen children ranging in age from 2 months to 12 years were treated for strabismus by botulinum injection of extraocular muscles. An average of 1.7 injections per patient was given. Follow-up at an average of 26 months after the last injection (minimum, 6 months) was available on 362 children (88%). The frequency of correction of 10 prism diopters (PD) or less in various groups of strabismus cases was: all 362 cases, 61%; all esotropia, 66%; infantile esotropia, 65%; and exotropia, 45%. Smaller deviations (10-20 PD) were more frequently corrected (73%) than were larger deviations (20-110 PD, 54%). The frequency of correction to 10 PD or less of previously operated cases was not different from that of unoperated cases. There was no globe perforation, amblyopia, or visual loss produced by the injection treatment in this series.

Elements of the peripheral oculomotor apparatus.

ABSTRACT In awake patients the rectus muscles exert about 15 grams force on the globe. Stiffness of orbital tissues to rotation is nearly linear and is about 0.5 gm/degree. Stiffness of rectus muscles to rotation is about 1.0 gm/degree, and is the same from 30° of abduction to 30° of adduction. These values can be separately determined. The balance between them should help predict the type and amount of surgery required to correct an imbalance.

Horizontal saccadic velocities in Duane's syndrome.

Horizontal ocular saccadic velocities were measured by electro-oculography in 33 patients with Duanes syndrome. In 28 patients with limited abduction associated with retraction on adduction (Type 1), abduction saccadic velocity was markedly reduced while adduct-on saccades were moderately slow. In three patients with exotropia and good abduction but associated limited adduction and retraction on adduction (Type 2), abduction velocity was good, while adduction saccadic speed was slow. In two patients with limited abduction and adduction with retraction on adduction (Type 3), abduction and adduction saccadic velocity was appreciably slow. Ocular electromyographic testing selected patients indicated that slow abduction saccades could be explained by absence of lateral rectus muscle recruitment, while slow adduction saccadic speed could be explained by paradoxical innervation of the lateral rectus muscle.

Diagnostic injection of Xylocaine into extraocular muscles.

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 Duanes syndrome, superior oblique palsy, and other situations where abnormal muscle insertions or innervations make diagnosis of the muscle responsible for an eye movement anomaly difficult and surgery unpredictable.

Botulinum Toxin Treatment of Strabismus

In the 12 years since the beginning of strabismus treatment by botulinum toxin at Smith-Kettlewell, about 6,000 cases have been treated world-wide. Injection is particularly attractive in adults, representing an office procedure of a few minutes, requires no incision, leaves no scar, and is cheaper.

Bupivacaine injection of the lateral rectus muscle to treat esotropia

PURPOSE We report results of a pilot trial of bupivacaine injection into extraocular muscles as a method of enlarging and strengthening the muscles to treat strabismus. METHODS Bupivacaine, in volumes from 1.0 to 4.5 mL and concentrations from 0.75% to 3.0%, was injected into 1 lateral rectus muscle in each of 6 patients with comitant esotropia with the use of the electrical activity recorded from the needle tip to guide injection. Magnetic resonance imaging was performed before and at intervals after injection to estimate changes in muscle size. Clinical measures of alignment were made before and at intervals after injection. Two patients required a second injection for adequate effect. RESULTS Four patients showed improved eye alignment, averaging 12(Delta), measured an average of 367 days after the last injection (range, 244-540 days). Two patients were substantially unchanged. Alignment improvement for all 6 patients averaged 8(Delta) (range, 0-14(Delta)). Volumetric enlargement of the injected muscle, computed from magnetic resonance images, was 6.2% (range, -1.5% to 13.3%). There was a positive correlation between alignment change and muscle enlargement averaging 0.65. Injection caused a retrobulbar hemorrhage in an unchanged patient that cleared without affecting vision. CONCLUSIONS Bupivacaine injection improved eye alignment in 4 of 6 esotropic patients. There was a positive correlation between improved eye alignment and increased muscle size. Clinical and laboratory studies are underway to determine optimal dosages, effects in other strabismus conditions, and differential effects of bupivacaine on contractile and elastic muscle components.

Disinserted Extraocular Muscles

In two patients, a muscle that slipped from the globe posteriorly created the clinical pattern of reduced rotation amplitude, reduced saccadic velocity, reduced active force, and increasing exophthalmos with gaze into the field of action of the muscle. The muscle was surgically identified by an electronic stimulator that caused the muscle to contract, thus allowing the surgeon to fell it pull on the forceps or see its traction on adjacent tissues.

Bupivacaine Injection Remodels Extraocular Muscles and Corrects Comitant Strabismus

PURPOSE To evaluate the clinical effectiveness and anatomic changes resulting from bupivacaine injection into extraocular muscles to treat comitant horizontal strabismus. DESIGN Prospective, observational clinical series. PARTICIPANTS Thirty-one comitant horizontal strabismus patients. METHODS Nineteen patients with esotropia received bupivacaine injections in the lateral rectus muscle, and 12 patients with exotropia received bupivacaine injections in the medial rectus. Sixteen of these, with large strabismus angles, also received botulinum type A toxin injections in the antagonist muscle at the same treatment session. A second treatment was given to 13 patients who had residual strabismus after the first treatment. MAIN OUTCOME MEASURES Clinical alignment measures and muscle volume, maximum cross-sectional area, and shape derived from magnetic resonance imaging, with follow-up examinations for up to 3 years. RESULTS At an average of 15.3 months after the final treatment, original misalignment was reduced by 10.5 prism diopters (Δ; 6.0°) with residual deviations of 10Δ or less in 53% of patients. A single treatment with bupivacaine alone reduced misalignment at 11.3 months by 4.7Δ (2.7°) with residual deviations of 10Δ or less in 50% of patients. Alignment corrections were remarkably stable over follow-ups for as long as 3 years. Six months after bupivacaine injection, muscle volume had increased by 6.6%, and maximum cross-sectional area had increased by 8.5%, gradually relaxing toward pretreatment values thereafter. Computer modeling with Orbit 1.8 (Eidactics, San Francisco, CA) suggested that changes in agonist and antagonist muscle lengths were responsible for the enduring changes in eye alignment. CONCLUSIONS Bupivacaine injection alone or together with botulinum toxin injection in the antagonist muscle improves eye alignment in comitant horizontal strabismus by inducing changes in rectus muscle structure and length.