Tonic pupil after botulinum toxin-A injection for treatment of esotropia in children

Golden Indications and an Overview on the Use of Botulinum Toxin in Strabismus

Botulinum toxin A (BTXA) is considered a pharmacological agent that may provide an alternative treatment to surgery in strabismus. It can be used as both a diagnostic and therapeutic agent in various concomitant, paralytic, and restrictive disorders. The major advantage of BTXA treatment is that it is non-invasive and does not impact the patient's chance for future surgery in case of an unfavorable response. In some selected disorders, BTXA has become the primary choice of treatment, whereas surgery is found to be more effective in others. Accumulated knowledge and experience have demonstrated that BTXA is more than merely an alternative treatment and has additional specific indications such as in unstable deviations and as an adjunct to surgery. Patients with recurrent deviations despite multiple surgeries are also good candidates for BTXA treatment. Although the major expectation is to obtain a permanent result, BTXA can also be used as a maintenance treatment. This paper mainly focuses on the current indications for the use of BTXA in strabismology, with special emphasis on ideal first-choice applications referred to as "golden indications," within the scope of the author's own experience with the use of BTXA over 30 years.

[Long term outcomes of botulinum toxin injections in infantile esotropia]

PURPOSE

To evaluate long terms outcomes of botulinum toxin in infantile esotropia by measuring the amount of microtropia 24 months after injection. Secondary purpose was to identify predictive factors of microtropia.

METHODS

A retrospective, single-center study was performed at the university medical center in Bordeaux between 2001 and 2018, including all patients with infantile esotropia greater than 20 D. All patients received 5 or 7,5 IU of botulinum toxin A in each medial rectus, once or twice depending on the angle of deviation after the first injection and after wearing full optical correction at least two months. We noted the angle at 1, 6, 12 and 24 months, the occurrence of any complications and the need for later strabismus surgery. The primary endpoint was the achievement of a microtropia less than 8 diopters (D) at 24 months post-injection. We evaluated the predictive factors for microtropia with a Fischer's test.

RESULTS

We included 30 patients with esotropia greater than 20 D. The mean follow-up after injection was 48 months ±30. The mean age was 16.24 months (7-29 months) with a female predominance in the population (SR=0.43). The mean pre-injection deviation was 41.25±12.17 D. The majority of patients were mildly (40%) or moderately (40%) hyperopic. At 24 months, 46.7% microtropias were obtained (95% CI: 28.9%-64.5%). The change in mean angle at 1, 6, 12 and 24 months post-injection was -8.57±25.21 D; 14.48±13.40 D; 18.38±12.07 D and 21.23±14.97 D, respectively. No factors were predictive of microtropia. Of the 30 children, 3 had transient ptosis requiring strips and 12 showed an exotropia at 1 month. All complications were self-limited and without consequences. 3 children had a second injection of botulinum toxin, which in 2/3 of the cases resulted in a long-lasting microtropia. 26.7% (n=8) of the children underwent secondary surgery. Obtaining a microtropia 24 months after injection statistically significantly reduced the need for secondary strabismus surgery: 92.9% P=0.039% CI 95% (0.002; 1.0606).

CONCLUSION

Botulinum toxin appears to be a less invasive and more conservative alternative to surgery in children with infantile esotropia. In 46.7% of cases, microtropia is achieved. An improvement was noted in 90% (n=27) of the children with a reduction of half (21.23 D) of the mean post-injection angle at 24 months. When effective, it significantly reduces the need for secondary surgery.

Use of Botulinum Toxin in Ophthalmology

Botulinum toxin is an important treatment for many conditions in ophthalmology, including strabismus, nystagmus, blepharospasm, hemifacial spasm, spastic and congenital entropion, corneal exposure, and persistent epithelial defects. The mechanism of action of botulinum toxin for both strabismus and nystagmus is the neuromuscular blockade and transient paralysis of extraocular muscles, but when botulinum toxin is used for some forms of strabismus, a single injection can convey indefinite benefits. There are two unique mechanisms of action that account for the long-term effect on ocular alignment: (1) the disruption of a balanced system of agonist-antagonist extraocular muscles and (2) the reestablishment of central control of alignment by the binocular visual system. For other ocular conditions, botulinum toxin acts through transient paralysis of periocular muscles. Botulinum toxin is a powerful tool in ophthalmology, achieving its therapeutic effects by direct neuromuscular blockade of extraocular and periocular muscles and by unique mechanisms related to the underlying structure and function of the visual system.

The Use of Botulinum Toxin in Strabismus Treatment

There is a long and extensive experience with the use of Botulinum Toxin type A (BoNT-A) injection in the treatment of different types of strabismus and oculomotor palsies. The frequency of its use varies depending on the country and institution. It is a short procedure, may reduce general anesthesia exposure, causes minimal scarring compared to surgery, and can be proposed as an early treatment in unstable strabismus. Over many years, the experience of using BoNT-A indications has been refined and new applications have been reported. The use of BoNT-A in the postoperative period, after strabismus surgery or during surgery, can also be beneficial.

Eyeing up the Future of the Pupillary Light Reflex in Neurodiagnostics

The pupillary light reflex (PLR) describes the constriction and subsequent dilation of the pupil in response to light as a result of the antagonistic actions of the iris sphincter and dilator muscles. Since these muscles are innervated by the parasympathetic and sympathetic nervous systems, respectively, different parameters of the PLR can be used as indicators for either sympathetic or parasympathetic modulation. Thus, the PLR provides an important metric of autonomic nervous system function that has been exploited for a wide range of clinical applications. Measurement of the PLR using dynamic pupillometry is now an established quantitative, non-invasive tool in assessment of traumatic head injuries. This review examines the more recent application of dynamic pupillometry as a diagnostic tool for a wide range of clinical conditions, varying from neurodegenerative disease to exposure to toxic chemicals, as well as its potential in the non-invasive diagnosis of infectious disease.

The resurgence of botulinum toxin injection for strabismus in children

PURPOSE OF REVIEW

The present review discusses recent advances in the use of botulinum toxin for the management of strabismus in children.

RECENT FINDINGS

Botulinum toxin injection produces similar results compared to surgery for certain subtypes of strabismus, especially acute onset esotropia. It may be more effective in many subtypes of esotropia where surgery has been less reliable, including partially accommodative esotropia, esotropia associated with cerebral palsy, and thyroid eye disease.

SUMMARY

Small retrospective studies have demonstrated the efficacy of botulinum toxin in the treatment of many types of pediatric strabismus, providing some guidance for clinicians to determine which patients would benefit most from this intervention. Although administration of botulinum toxin is generally accepted as a reasonable option in select cases, many strabismus surgeons have not fully embraced the treatment, in part because of perceived disadvantages compared to surgery and difficulty in identifying subsets with the highest potential for therapeutic success. A recent study compared the administration of botulinum toxin in children with acute-onset esotropia to surgical correction and found botulinum toxin had a statistically equal success rate, but with the advantage of significantly less time under general anesthesia. In addition, botulinum toxin has been recently tried in patients with partially accommodative esotropia, esotropia associated with cerebral palsy, cyclic esotropia, and in patients with thyroid eye disease. The present review will discuss current clinical recommendations based on recent studies on the use of botulinum toxin in children with strabismus.