Evaluation of The Techniques in Correcting Large-Angle Exotropia

The aim of this study is to evaluate the techniques of combined lateral rectus muscle recession with hang back and combined lateral rectus muscle recession with z-tenotomy in correcting large-angle exotropia.

Strabismus was defined as any heterotropia at near or distance fixation, or both, on cover testing. Micro strabismus was known as a deviation of fewer than 10 prism diopters (PD). Different studies have defined large angle deviation as 35 Δ , 40 Δ, 50 Δ and 60 Δ.

Studies revealed that during the first decade of life, exotropia is most prevalent with intermittent exotropia and convergence insufficiency are the most frequent. Exotropic deviations include exophoria, infantile exotropia, intermittent exotropia, sensory exotropia and consecutive exotropia.

Large-angle constant exotropia has a negative impact on the patients and surgical treatment of exodeviations improves the patient's psychosocial functioning. Hence, many surgical techniques have been described for management of exotropia, including bilateral lateral rectus recessions or recess/resect procedures. Botulinum toxin injection combined with recession-resection procedures was used as another surgical technique.

As a fact large-angle exotropia usually requires greater amounts of surgery, often a surgery on a greater number of extraocular muscles. Hence, 3 or 4 horizontal muscle surgery was performed for correcting large angle exotropia. Single-staged three horizontal muscles surgery for large angle intermittent exotropia has been more successful.

Recently, medial rectus muscle surgery as bilateral medial rectus resection for primary large-angle exotropia has been used with successful results. A successful outcome of surgery was defined as deviation within 10 prism diopters for both distance and near.

Moreover, hang-back loop suspension surgical technique can be performed for lateral rectus (LR) muscle recession. This technique can offer potential advantages over the conventional rectus muscle recession, including better exposure of the site of scleral sutures, lower risk of scleral perforation , shorter procedure duration and lower postoperative induced astigmatism.

On the other hand, the hang-back recession has some limitations as a potential unpredictability in surgical outcomes.Although previous reports suggest that the hang-back technique for LR recession for exotropia results in poorer surgical success and may require a different surgical dosage, another study proved that the hang-back surgical technique was as effective as conventional LR recession surgery for children with exotropia.

Furthermore, many studies were performed on Z-tenotomy technique as an alternative procedure for muscle weakening. This technique was applied for superior oblique muscle in cases with mild to moderate over depression in adduction with success rate 90%. An Other study has revealed that z-tenotomy up to 50% progressively reduces extraocular tendon force transmission, but Z-tenotomy of ≥50% is biomechanically equivalent in vitro to complete tenotomy.

In the past it was thought that muscle recessions with the muscle placed behind the anatomical equator of the globe would cause limitation of ocular rotation. Postoperative abduction limitation is one of the main problems in large recession and/or resection for primary and recurrent exotropia with large angle. It is generally thought that keeping the lateral rectus recession to no more than 8 mm prevents this complication. However, several studies revealed that large amounts of recession can be done without causing significant ocular movement limitation.

Eligibility Criteria:
Inclusion Criteria:

* Patients suffering from large angle exotropia; defined, in this study, as an angle of deviation ≥ 40 prism diopters (PD).

Exclusion Criteria:

1. Patients suffering from exotropia with angle \< 40 prism diopters (PD).
2. Patient with paralytic strabismus.
3. Patient with restrictive strabismus.
4. Patient with combined vertical and horizontal deviation.
5. Patients with previous strabismus surgery.
6. Patients who had previously been administered botulinum toxin A.
7. Patient refusal.