When medical therapy of strabismus (glasses, prisms, miotics, orthoptics) fail to straighten the ocular position adequately, surgery has been the next step in treatment. Although surgery is often successful, it does require hospitalization, an anesthetic, an incision, the use of sutures, and some time lost from school or work, in addition to a modest amount of ocular inflammation and discomfort.
In the early 1970s, Dr. Alan Scott, at the Smith-Kettlewell Institute of Visual Sciences in San Francisco, began studies utilizing various toxins injected into the extraocular muscles of monkeys. The aim was to cause a temporary ocular muscle palsy with a resultant change in ocular alignment after the effect of the toxin had worn off. After trying several substances, he concluded that a dilute solution of botulinum type A toxin (now called Oculinum) was the best material for his investigations. Following encouraging initial results in animals, Dr. Scott began utilizing this method in humans in the late 1970s (with NEI and FDA approval). Successful trials in patients1 allowed the introduction of this treatment modality to other strabismologists in 1982.
At the University of Rochester, we have treated 41 patients, 14 of whom have had a second injection and one who has had Five injections. Oculinum was injected through an EMG needle electrode to ensure proper location of the toxin. A volume of 0.1 cc was used with the dose varyingbetweenl x 10'3M-gto5 x 10-^g, depending upon the size of the deviation. There have been no systemic complications. At present, we have injected only teen-age and adult patients and have not treated children. Only horizontal rectus muscles have been injected. Local complications have included several patients with mild to moderate upper lid ptosis, which have all been temporary, and a few instances of sube onj u net i val hemorrhage. A small amount of patient discomfort has accompanied the injection, and two patients developed a hypertropia on the side of the injection with evidence of inferior rectus weakness with limitation of downgaze. The vertical deviation disappeared within four weeks.
FIGURE 1: Patient with 40 prism diopters of right esotropia and full adduction, right eye (left photograph). Five days following oculinum injection to the right medial reclus muscle, adduction of the right eye is limited to the midline (right photograph).
Our patients had horizontal strabismus, ranging in size from 20 to 80 prism diopters. In patients with esotropia, the medial rectus was treated, while cases of exotropia had the lateral rectus muscle injected. The resulting palsy remained from four to ten weeks, depending upon the dosage used. The eye fails to rotate in the direction of action of the treated muscle (Figure 1) and the resulting saccadic velocity is very slow (Figure 2).
The basic principle of therapy is that paresis of a rectus muscle for a period of weeks or months will allow the antagonist muscle to shorten and tighten. When the paretic muscle recovers, the increased stiffness of the antagonist will keep the eye in an improved position, even in a straight position if the initial deviation was not very large. Repeat injections are possible.
Oculinum therapy has worked very well in patients with rectus muscle paralysis of fairly short duration (less than four to six weeks). If the paralytic muscle recovers, the eyes will remain aligned without further treatment, as antagonist muscle contracture (causing a continued deviation) has been avoided (Figure 3). If recovery from the paralysis does not occur, the injection will be of only temporary help and will not result in long term alignment (Figure 4).
Patients seem especially interested in this therapeutic approach if they have undergone one or several "unsuccessful" surgical procedures. This sometimes causes difficulty locating the muscle with the EMG needle electrode, but with some experience, can be overcome.
Significant advantages include:
1. the procedure takes only 10 minutes;
2. it can be done entirely in an outpatient setting;
FIGURE 2: Electro-oculographic tracing of horizontal saccades in the right eye, five days after Oculinum injection to the right medial rectus muscle. Saccades right fri are rapid while saccades left (Il are slow. Upper tracing - eye position; lower tracing - peak velocity.
3. only topical anesthesia is required;
4. it is easily repeatable;
5. time is not lost from school or employment;
6. it is less costly.
Disadvantages to consider are:
1. temporary overcorrection may cause diplopia (this can be managed with a patch);
FIGURES: Left sixth nerve palsy with 60 prism diopters of left esotropia t right photograph). Tivo months following Oculinum injection to left medial rectus muscle, the eyes are straight (left photograph) and horizontal rotations were full, left eye.
FIGURE 4: Long-standing right lateral rectus paralysis with SO prism diopters of right esotropia tieft photograph). One week following Oculinum injection to the right medial rectus muscle, the eyes are parallel !note the nasal subconjunctiua! hemorrhage, right eye) (center photograph). Tiiio months following injection, the right esotropia has returned (right photograph).
2. a prolonged period of ptosis may follow injection of the superior rectus muscle;
3. it is possible to perforate the globe with the EMG needle electrode;
4. insurance frequently does not provide coverage for an experimental procedure;
5. the long-term effects are still not known.
When children are treated, ketamine anesthesia has been used in the recovery room setting of the hospital. DrAlan Scott has had experience in children and believes this method has value in these patients. The children can be discharged several hours after injection.
It would seem that Oculinum injection for strabismus is an innovative new form of therapy that has clear benefits and advantages in certain cases. Further experience will allow us to place this technique in its proper role among the treatments now available for the strabismus patient.
1. Scott AB: Botulinum toxin injection of eye muscles to correct strabismus. TrAm Qphthalmol Soc 1981; 79:735-770.