Surgical outcomes of four inferior oblique weakening techniques: a graded, severity-based approach

Inferior oblique muscle overaction (IOOA) is a common cause of vertical strabismus. Most published comparisons cover two or three techniques. We evaluated 1-year outcomes of a severity-guided algorithm comparing four weakening techniques for IOOA: disinsertion, myectomy, anterior transposition (AT), and nasal transposition (NT).

In this retrospective comparative cohort study, 286 eyes of 200 patients with IOOA (grade + 1 to + 4) were treated by disinsertion (n = 141), myectomy (n = 29), AT (n = 94), or NT (n = 22), selected by the operating surgeon according to preoperative IOOA severity (minimum 1-year follow-up). Pre- and postoperative IOOA grade, abnormal head posture (AHP), and horizontal deviation were compared with non-parametric tests; a patient-level sensitivity analysis was performed. Success (postoperative IOOA grade 0 or + 1 without underaction) is reported with 95% Wilson confidence intervals.

The cohort's median preoperative IOOA grade was + 3 and fell to 0 at 1 year (p < 0.001). As expected from the indication-based design, preoperative IOOA differed across groups (Kruskal-Wallis p < 0.001): disinsertion was used for a median grade of + 3 (range + 1 to + 4); transposition techniques were used for more severe cases (median + 3.5 to + 4). At 1 year, the median postoperative IOOA was 0 in every group (p = 0.098 between techniques). Patient-level sensitivity analysis preserved the same conclusion (Kruskal-Wallis postoperative p = 0.075). Success (postoperative IOOA grade 0 or + 1) was achieved in 92 to 95% of patients in each arm, with overlapping 95% confidence intervals (Disinsertion 93.1%, 95% CI 86.4 to 96.6%; Myectomy 89.5%, 95% CI 68.6 to 97.1%; anterior transposition 92.1%, 95% CI 82.7 to 96.6%; nasal transposition 94.1%, 95% CI 73.0 to 99.0%). AHP prevalence fell from 54.5% to 15.0%, and no case of anti-elevation syndrome was observed.

Within a severity-guided, real-world algorithm, the four techniques achieved comparable short-term IOOA control when applied within their intended severity ranges; because assignment was indication-driven, this reflects within-indication performance, not equivalence. This short-term parity should be read cautiously and may not hold over time: a 1-year follow-up cannot capture the late recurrences. Prospective studies with longer follow-up, etiology stratification, dissociated vertical deviation documentation, and functional endpoints are needed.