Extraocular Muscle Transplantation Surgery for Primary Treatment of Extra Large-angle Squint.

Purpose: Large-angle horizontal ocular deviations will commonly require bilateral surgery to correct the primary ocular deviation. However, considering the need for full correction with one surgical procedure and patients' reluctance to be operated on the good eye, such large horizontal ocular deviations may be managed with true muscle transplantation. The authors present a case series of patients who underwent this procedure and develop a surgical table to guide management.

Methods: Patients with horizontal squints measuring 80 prism diopters (PD) or larger in all age groups who underwent extraocular muscle transplantation surgery between January 2019 and June 2022 in Nigeria were included. Preoperative deviation of the squint, sensory evaluation, surgical dosage, and outcomes were documented. Part of the resected muscle was transplanted to give additional recession in the antagonist muscle. Success was defined as deviation corrected by 60% or more or postoperative ocular alignment within 10 PD or less, six weeks postoperatively.

Results: Fourteen patients with extra-large-angle strabismus were operated. Male/female ratio was 0.6:1. Mean preoperative deviation of 89.6 $\pm$ 9.3 collapsed to 6.6 $\pm$ 1.8 PD at six weeks and continued to improve to a mean deviation of 2.5 PD at six months postoperatively. When the subgroup of patients who were $<$ 18 years were analyzed, the outcome was equally successful; preoperative deviation of 89.4 PD collapsed to 1.4 PD, six months postoperatively. There were equal success rates when those with sensory strabismus were compared with those with binocular vision; preoperative deviation of 92.5 PD in the sensory group and 88.5 PD in the binocular group collapsed to 5.9 PD and 1 PD, respectively, six months after surgery.

Conclusion: A viable alternative for treating extra-large-angle strabismus in adults and children in developing countries was described with good postoperative outcome. In addition, a new expanded surgical dosage table for muscle transplantation surgery corrections of up to 130 PD was developed.