Dr.SAYALI MAHAJAN

Dr. DEEPTI P., Dr.Krishna Prasad R

Abstract

Purpose: To determine effect of botulinum toxin(BT) augmentation on bimedial recession surgery in children with large-angle esotropia(ET)> 50 PD

Design: Prospective interventional case series in a tertiary centre in south India. 14 children with large angle ET >50PD underwent bimedial recession augmented with 2.5 units of BT to each MR muscle intraoperatively and were followed up for 2 years. Surgery was considered successful if patients had <10 PD of deviation and did not require additional surgery

Results: The mean preop deviation was 65 PD(range 50–80 PD). Successful outcome was seen in 10 of 14 patients (71.42%), p<0.001. Of these 10, 7 had sensory fusion on worth 4 dot test. Of the rest 4, 3 had residual small angle ET and 1 developed consecutive exotropia

Conclusions: For children with large angle ET (>50 PD), 2 muscle surgery may not be adequate. BT augmentation is a safer alternative, preserving third muscle for future need and helps to achieve satisfactory binocular alignment

Full Text

Botulinum toxin augmented strabismus surgery in large angle esotropia- Saviour in disguise

Purpose:

To determine effect of botulinum toxin (BT) augmentation on bimedial recession surgery in children with large-angle esotropia (ET)> 50 prism diopters (PD)

Design:

Prospective interventional case series in a tertiary centre in south India. Fourteen children with large angle ET > 50PD underwent bimedial recessions augmented with 2.5 units of BT to each MR muscle intraoperatively and were followed up for 2 years. Surgery was considered successful if patients had <10 PD of deviation and did not require additional surgery.

Results:

The mean preop deviation was 65 PD (range 50–80 PD). Successful outcome was seen in 10 of 14 patients (71.42%), p<0.001. Of these 10, 7 had sensory fusion on worth 4 dot test. Of the rest 4, 3 had residual small angle ET and 1 developed consecutive exotropia

Conclusions:

For children with large angle ET (>50 PD), two muscle surgery may not be adequate. BT augmentation is a safer alternative, preserving third muscle for future need and helps to achieve satisfactory binocular alignment

Introduction

Infantile esotropia is defined as an esodeviation of unknown etiology that manifestsbefore the age of 6 months. It is the most common type of strabismus in infancy, with an estimated prevalence of 0.3-0.5%.1,2 It is seen that the deviation is not present at birth but develops around the age of 2-4 months.1 When the angle reaches above 40PD it is unlikely to resolve by itself.3,4 The purpose of this study is to report long-term outcomes for children with large-angle infantile esotropia.

Materials and methods

The study design was a non-randomized clinical study and was conducted at a tertiary-care pediatric hospital. Institutional Review Board (IRB) approval was obtained prospectively. The study conformed to the research adhered to the tenets of the Declaration of Helsinki.

The study was conducted for all patients less than 7 years of age with esotropia of at least 50 PD. Patients were excluded who had undergone previous ocular surgery, who had major neurologic abnormalities, or who were unavailable for follow-up for a minimum period of six weeks following surgery.

Deviation was measured by prism cover test on accommodative target at distance (6 m) and near (33 cm); measurements within 5 PD on two consecutive visits were required preoperatively. Measurements for children too young for accurate prism cover test measurements at distance were obtained at near only. Versions were recorded. For cycloplegic refractions, instillation of one drop (20 µL) of 1.0% cyclopentolate hydrochloride was followed by a second drop five minutes later; retinoscopy was performed after a 40-minute interval. Refractions were repeated on subsequent visits until retinoscopic findings agreed within 0.5 diopter (D). Two patients had a cycloplegic refraction of +2.00 D spherical equivalent or greater and these were placed in their full cycloplegic correction before surgery. Any patient who had amblyopia was treated by full-time occlusion therapy until the visual acuities of the two eyes were less than one line’s difference, or until the fixation pattern was equal. The sensory status was assessed by fusion to Worth’s four-dot test and by the Titmus stereoacuity test. A total of 14 children met the criteria for the study. They underwent bimedial recessions of 5- 6.5 mm augmented with 2.5 units of BT to each MR muscle intraoperatively.

Results

The follow-up period ranged from six weeks to 2 years. Prism cover test measurements were performed under the same conditions as preoperatively. A good surgical result was defined as orthophoria +/- 10 PD both at distance and near. An esotropia greater than 10 PD was considered an undercorrection, and exotropia greater than 10 PD an overcorrection.

The mean preop deviation was 65 PD (range 50–80 PD). Successful outcome was seen in 10 of 14 patients (71.42%), p<0.001. Out of these 10 patients, 7 had sensory fusion on worth 4 dot test. Three patients had residual small angle ET and one developed consecutive exotropia.

Transient complications were common, including 2 cases (14.2%) of transient overcorrection and 1 cases (7.14%) of transient ptosis which resolved after 4 weeks. No patients developed a transient vertical deviation. There were no long term complications from botulinum toxin injection.

Discussion

The treatment of infantile esotropia consists of a uniform approach or a selective one. Uniform surgery consists of either bimedial recessions or a monocular recession-resection. The selective surgery consists of operating three or four horizontal muscles, tailoring the amount of surgery to the amount of preoperative deviation by performing graded amounts of resection of one or both lateral rectus muscles in addition to bimedial recessions.5 While studies on three-muscle surgery have reported good early success rates,5, 6, 7 Many of them studies have also reported high rates of sequential exotropia of up to 24%.8

Another treatment approach designed to avoid undercorrection is to perform “supra-maximal” medial rectus muscle recessions, but this is encountered with late overcorrection. Kushner9 cstudied that if the medial rectus muscle is recessed beyond a certain point, there is a significant risk of progressive late overcorrection.

The injection of botulinum toxin into the medial rectus muscles causes transient paralysis by blocking transmission at the neuromuscular junction.10 The direct effects of botulinum toxin may be temporary but there can be a long-lasting effect on ocular alignment.11,12 One advantage of using botulinum toxin is that a standard dose can be used for a range of deviations, which is useful because it is difficult to obtain precise measurements in young infants.13,14 A case series of 60 patients reported a high success rate (close to 90%) with botulinum toxin injections, especially in children <7 months old.15 However, a large comparative study found that botulinum toxin was much less effective than surgery when the angle of deviation was greater than 35 PD, suggesting that botulinum toxin alone is likely a poor choice for patients with large angle esotropia.13

Early surgery may help to promote the development of binocularity and stereoacuity.16,17 However, a study by the Pediatric Eye Disease Investigator Group found that the angle of deviation is more variable at a young age.14

This study has weaknesses. The treatment strategies were not standardized. The mean follow-up was 2 years, further changes in alignment may continue to occur years and decades after surgery. Longer term data is needed to determine if and how post-operative binocularity and stereoacuity are affected by the timing of surgery.

Future studies comparing different treatment strategies would be useful since most studies to date have reported outcomes using a uniform treatment approach. Longer-term studies would also be helpful to inform treatment decisions and provide more accurate prognostic information for children with large-angle, infantile esotropia.

References

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