Long-term efficacy of superior oblique suture lengthening surgery for A-pattern strabismus: a retrospective observational study

A-pattern strabismus, often associated with superior oblique overaction (SOOA), presents with greater horizontal deviation in downgaze than upgaze and may lead to significant ocular misalignment. Superior oblique suture lengthening offers a quantifiable alternative to traditional weakening procedures. The aim of this study was to evaluate the long-term efficacy of unilateral and bilateral superior oblique suture lengthening in treating A-pattern strabismus caused by SOOA. This single-centre retrospective observational study included 35 patients who underwent unilateral ( n = 14) or bilateral ( n = 21) superior oblique suture lengthening between January 2013 and August 2023. All patients were followed for over one year. Preoperative and postoperative assessments included measurements of A-pattern deviation, SOOA grade, objective cyclotorsion, vertical strabismus, and binocular vision. Statistic al analysis was performed using SPSS and Python software, employing paired t-tests, Wilcoxon rank-sum tests, and correlation analyses. The A-pattern improved in all patients after surgery.The mean correction was 16.07 ± 4.34 prism dioptres (PD) in unilateral cases and 21.71 ± 7.58 PD in bilateral cases. Vertical strabismus in the unilateral group improved by 13.86 ± 3.21 PD, though five patients developed reverse vertical strabismus in the contralateral eye. SOOA scores improved from + 3 preoperatively to 0 postoperatively in both groups. Mean cyclotorsion correction was 7.14 ± 3.90° (unilateral) and 8.10 ± 4.17° (bilateral). Binocular visual function improved in 20 patients. Suture extension showed a significant positive correlation with both preoperative SOOA grade and postoperative change in SOOA. A similar correlation was observed between preoperative cyclotorsion and torsional correction. Unilateral surgery had no significant effect on the contralateral eye. No complications, including rotational diplopia or muscle insufficiency, were observed during long-term follow-up.A suture length optimization prediction model was developed based on Generalized Additive Models to address small-sample clinical data characteristics. Superior oblique suture lengthening is a safe and effective surgical method for correcting A-pattern strabismus and SOOA. It achieves stable alignment, improves torsional outcomes and binocular function, and shows no measurable effect on the contralateral eye. These results support the use of this technique as a long-term solution for managing superior oblique overaction.