This is a multi-center, randomized single-blind controlled trial to compare the effectiveness of S-BLR with C-BLR for the treatment of CI-IXT in children.

Specific Aim 1 (Primary): To compare the surgical successful rate of S-BLR with C-BLR for the treatment of CI-IXT in children.

Specific Aim 2 (Secondary): To study the suboptimal surgical outcomes between S-BLR and C-BLR for the treatment of CI-IXT in children.

Using conventional surgical procedures, higher postoperative near undercorrection and/or distant overcorrection rates were observed in CI-IXT. To achieve better outcome, S-BLR was introduced. Previous studies showed its efficacy in reducing near exodeviation, distant exodeviation, and NDD. So far, only limited studies have directly evaluated the surgical outcomes between S-BLR and C-BLR. The pilot study done by Snir et al included 12 patients with S-BLR and 6 patients with C-BLR and the success rates of S-BLR vs C-BLR were 92% vs 0 at one-year follow-up. The retrospective study done by Song et al included 17 patients undergoing S-BLR and 14 patients undergoing C-BLR. With stricter successful criteria, the success rates of S-BLR vs C-BLR were 35% vs 7% at six-month follow-up. A large randomized trial is needed to compare the surgical successful rate and suboptimal surgical outcomes of S-BLR with C-BLR in children with CI-IXT.

The proposed trial will be conducted in 6 different study sites working in the field of pediatric ophthalmology and strabismus.Each site will have one certified surgeon to do all surgeries. Under general anesthesia, the LR recession is performed using an inferior-temporal fornix incision. For S-BLR, the lower horn of the LR is recessed based on near exodeviation and the upper horn is recessed based on distant exodeviation. For C-BLR, the LR is recessed based on distant exodeviation. Surgical dose is according to the largest preoperative exodeviation at distance (6 meters) or near (1/3 meter) by the prism and alternate cover test(PACT). The extent of the recession is based on Parks' surgical dosage schedule.

Inclusion Criteria:

• Exodeviation at least 15 at distance (6 meters);
• Exodeviation at most 50 at near (1/3 meter);
• Greater exodeviation at near than at distance by 10 or more;
• Control score of exodeviation greater than 3;
• Best-corrected visual acuity of 20/40 or better in the worse eye, and interocular difference of less than 2 lines;
• Myopia5.00D, hyperopia3.0D and anisometropia≤2.5D based on cycloplegic refraction
• Optical correction needed for at least 2 weeks before evaluation of exodeviation: myopia0.5D or astigmatism1.5D in either eye, or anisometropia1.0D;
• Written informed consent given by participants and their parents or legal guardians.

Exclusion Criteria:

• Prior strabismus surgery or botulinum toxin injection;
• Coexisting vertical deviation greater than 5, oblique muscle dysfunction, torsional deviation, dissociated vertical deviation, A-V pattern, or other conditions requiring horizontal rectus transposition, oblique surgery or vertical rectus surgery;
• Paralytic or restrictive strabismus;
• Lateral incomitance (greater exodeviation in right or left gaze position than in primary position by 5 or more with appropriate optical correction);
• Ocular disease other than strabismus or refractive error;
• Previous intraocular or refractive surgery;
• Craniofacial malformations affecting the orbit;
• Significant neurological disorders;
• Birth date34 weeks or birth weight1500 gram.

Abbreviations: CI-IXT, convergence insufficiency intermittent exotropia; D, diopter.

We concerns about patient privacy issues and it's better to protect the publication potential.