The Role of Botulinum Toxin in Decompensated Strabismus

A Comparison of Chemodnervation to Incisional Surgery for Acute, Acquired, Comitant Esotropia: An International Study

PURPOSE

To compare the efficacy of botulinum toxin injections to strabismus surgery in children with acute, acquired, comitant esotropia (ACE), and to investigate factors predicting success.

DESIGN

International, multi-center nonrandomized comparative study METHODS: Setting: Cloud-based survey.

STUDY POPULATION

Children aged 2 to 17 years who underwent a single surgical intervention for ACE.

INTERVENTIONS

Botulinum toxin injection ("chemodenervation" group) or strabismus surgery ("surgery" group).

MAIN OUTCOME MEASURES

Primary measure: success rate at 6 months in propensity-matched cohort, defined as total horizontal deviation of 10 prism diopters or less with evidence of binocular single vision. Secondary measure: Risk factors for poor outcomes in the full cohort.

RESULTS

Surgeons from 19 centers contributed. There were 74 patients in the chemodenervation group and 97 patients in the surgery group. In the propensity-matched data (n = 98), success rate was not significantly different at 6 months (70.2% vs 79.6%; P = .2) and 12 months (62.9% vs 77.8%; P = .2), but was significantly lower in the chemodenervation group at 24 months (52% vs 86.4%; P = .015). Irrespective of treatment modality, treatment delay was associated with lower success rates at 6 months, with median time from onset to intervention 4.5 months (interquartile range (IQR): 2.1, 6.7) in the success group and 7.7 months (IQR: 5.6, 10.1) in the failure group (P < .001).

CONCLUSIONS

In children with ACE, success rate after chemodenervation was similar to that of surgery for up to 12 months but lower at 24 months. Those with prompt intervention and no amblyopia had the most favorable outcomes, regardless of treatment modality.

Botulinum Toxin Injection for the Treatment of Strabismus: A Report by the American Academy of Ophthalmology

PURPOSE

To review the available evidence comparing the effectiveness of extraocular muscle botulinum toxin type A (BTXA) injection with eye muscle surgery for restoring ocular alignment in children and adults with nonparalytic, nonrestrictive horizontal strabismus.

METHODS

Literature searches in the PubMed Cochrane Library, and clinical trial databases with no date restrictions, but limited to articles published in English, were conducted last on January 10, 2021. The searches yielded 515 citations, 40 of which were reviewed in full text by the first author. Fourteen articles met the criteria for inclusion (randomized or nonrandomized comparative studies, or case series with a minimum 50 patients; evaluating extraocular muscle BTXA injection for initial or repeat treatment of horizontal, nonparalytic, nonrestrictive strabismus; with at least 6 months of follow-up) and were graded by a methodologist.

RESULTS

The 14 included studies consisted of 2 randomized clinical trials, 3 nonrandomized comparative studies, and 9 case series. All 5 comparative studies were graded level II evidence, and the 9 case series were graded level III evidence. Successful motor outcomes after BTXA injection were relatively consistent across 4 of the 5 comparative studies at 60%, when adjustment was made for differential selection bias in 1 of the studies. In the 4 studies, successful motor outcomes after surgery ranged from 66% to 77% with a mean follow-up of 23 to 75 months, and the outcomes were not significantly different from those after BTXA injection. In the fifth level II study, success was significantly higher with BTXA injection than with surgery (94% vs. 72%). The level III BTXA case series demonstrated higher motor success rates of 87% to 89% when children were treated in 2 muscles at a time; rates were lower in adults treated with single-muscle BTXA injection.

CONCLUSIONS

Extraocular muscle injection of BTXA achieves a high rate of successful motor alignment, comparable with that achieved after eye muscle surgery for nonparalytic, nonrestrictive horizontal strabismus. Good alignment may require multiple BTXA injections, and it is not yet clear whether sensory outcomes are equivalent for BTXA injections versus eye muscle surgery in young children.

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.

Botulinum toxin uses in strabismus: A review of the injections performed during one year in a general hospital

OBJECTIVE

To analyse the indications, dosage and efficacy of botulinum toxin A injection performed in patients in a Strabismus Department.

METHODS

In this prospective study, botulinum toxin A was injected into 28 patients diagnosed with strabismus. Data was obtained from the records of patients that were evaluated during 2013 in the Strabismus Unit of Rey Juan Carlos Hospital (Móstoles, Madrid, Spain) in order to assess the indications and dosage of botulinum toxin A use in strabismus, as well as its clinical effect and differences in paediatric and adult patients. The outcomes in the last visit, at least 14 months after the injections, were analysed.

RESULTS

An analysis was performed on the data from 11 children, 6 females (54.5%), and 17 adults, 11 males (64%). The mean age was 4.42±3.48 years and 58.71±18.07 years in the children and adult groups, respectively. The majority of cases in both groups were esotropia (81.8% in children and 47.1% in adults). However the pathologies in the adult group were quite heterogeneous, including 4 patients with exotropia (26.5%), 4 with hypertropia (26.5%), and one with isolated nystagmus (5.9%). The mean number of the botulinum toxin injections in children was 1.45±0.93, although 72.7% received a single injection. In the adult group, the mean number of injections was 3.27±1.41. There was a statistically significant difference between pre- and post-injection in the tropia and phoria measurements in children and adults group (P<.05). In both groups there was a statistically significant improvement in post-injection torticollis when compared with the pre-injection measurement (P<.05). An improvement in the stereoacuity could be detected in 4 children. Two children (18.2%) and 5 adults (29.4%) required subsequent surgical intervention. Eight adult patients (49.1%) complained of diplopia in the primary position, which was resolved in 6 cases with toxin injection, whereas 2 needed surgery for diplopia correction.

CONCLUSIONS

Botulinum toxin is a very useful tool in the management of strabismus, obtaining better sensory and motor results in children, but it is also effective as a symptomatic treatment in some types of strabismus in adults.

An external pilot study to test the feasibility of a randomised controlled trial comparing eye muscle surgery against active monitoring for childhood intermittent exotropia [X(T)]

INTRODUCTION

The evidence base for the treatment of strabismus (squint) is poor. Our main aim is to improve this evidence base for the treatment of a common type of childhood squint {intermittent exotropia, [X(T)]}. We conducted an external pilot study in order to inform the design and conduct of a future full randomised controlled trial (RCT).

METHODS

Children of between 6 months and 16 years with a recent diagnosis of X(T) were eligible for recruitment. Participants were recruited from secondary care at the ophthalmology departments at four UK NHS foundation trusts. Participants were randomised to either active monitoring or surgery. This report describes the findings of the Pilot Rehearsal Trial and Qualitative Study, and assesses the success against the objectives proposed.

RECRUITMENT AND RETENTION

The experience gained during the Pilot Rehearsal Trial demonstrates the ability to recruit and retain sites that are willing to randomise children to both trial arms, and for parents to agree to randomisation of their children to such a study. One child declined the group allocation. A total of 231 children were screened (expected 240), of whom 138 (60%) were eligible (expected 228: 95%) and 49 (35% of eligible) children were recruited (expected 144: 63% of eligible). Strategies that improved recruitment over the course of the trial are discussed, together with the reasons why fewer children were eligible for recruitment than initially anticipated. Attrition was low. Outcome data were obtained for 47 of 49 randomised children.

TRIAL PROCESSES AND DATA COLLECTION

The Trial Management processes proved effective. There were high levels of completion on all of the data collection forms. However, the feedback from the treatment orthoptists revealed that some modifications should be made to the length and frequency of the health service assessment and travel assessment questionnaires, thus reducing the burden on participants in the main trial. Modifications to the wording of the questions also need to be made.

MONITORING OF BIAS

Children who recruited to the trial were older and had more severe strabismus than those children eligible but declining participation. Strategies to account for this in a full trial are proposed.

REASONS FOR PARTICIPATION OR DECLINING STUDY

These were identified using qualitative interviews. The principal reasons for declining entry into the study were strong preferences for and against surgical treatment.

HARMS

There were no serious unexpected adverse events. Two children had overcorrection of their X(T) with reduction in binocular vision following surgery, which is in line with previous studies. No children in the active monitoring arm developed a constant strabismus although two showed some reduction in control.

CONCLUSIONS

The SamExo study has demonstrated that it is possible to recruit and retain participants to a randomised trial of surgery compared with active monitoring for X(T). For longer-term full RCTs, in order to maximise the generalisability of future studies, consideration needs to be given to planning more time and clinic appointments to assess eligibility and to allow consideration of participation; the greater use of research nurses for recruitment; and accommodating the strong preferences of some parents both for and against surgical intervention.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN44114892.

FUNDING

This project was funded by the NIHR Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 19, No. 39. See the NIHR Journals Library website for further project information.

[Treatment of the comitant adquired esotropia residual deviation]

PURPOSE

To review the therapeutic options in the management of residual esotropia, particularly focusing on the effectiveness of botulinum toxin.

METHODS

Retrospective study of cases of post-surgical residual esotropia treated in our hospital from January 1999 to January 2008. Visual acuity and motor outcomes were analysed in the patients who received botulinum toxin injection.

RESULTS

Of the 200 cases reviewed, 91% of the patients had a new surgery, 5% of patients refused any treatment, while 8 patients (4%) received botulinum toxin injection. Visual acuity (Snellen) before surgery, before toxin and after toxin injection in the right eye was 0.77 (SD 0.2), 0.86 (SD 0.2) and 0.97 (SD 0.2), respectively, and in the left eye: 0.76 (SD 0.1), 0.91 (SD 0.09) and 0.97 (SD 0.2), respectively. The percentage net change in the angle of deviation at far and near distance after toxin injection in the last follow-up was 41.66% and 10%, respectively. The mean follow-up after botulinum toxin injenction was 30.8 months. The success rate (ocular alignment in primary eye position) after toxin at the end of follow-up was 75%.

CONCLUSIONS

Residual esotropia may be managed with further surgery or with botulinum toxin injection. The first option is more common, but in selected cases botulinum toxin injection may provide very successful outcomes with a low incidence of complications.