To compare the outcome of inferior oblique (IO) disinsertion and myectomy in patients with unilateral congenital superior oblique palsy (SOP).

IO myectomy and disinsertion were performed for 34 and 28 consecutive unilateral congenital SOP patients, respectively. Success was defined as primary position hypertropia ≤ 5 PD and no hypotropia. In the cases with preoperative hypertropia ≤ 5 PD, success was defined as improvement of hypertropia and resolution of abnormal head posture (AHP).

Preoperative primary position hypertropia in IO myectomy and disinsertion groups was 15.8±7.4 and 14.5±7.3 PD, respectively (P=0.756). AHP was present in 85.3% and 85.7% of patients, respectively (P=1). Mean follow up duration was 7.5±6.7 and 6.9±3.0 months, respectively (P=0.637). Correction of hypertropia in primary position was more pronounced in IO myectomy (14.3±7.4 PD) compared to IO disinsertion (10.0±5.4 PD; P=0.013). Success was achieved in 91.2% and 60.7% of patients, respectively (P=0.006). However, persistence of AHP postoperatively was not different in the two groups (8.8% in myectomy group and 7.1% in disinsertion group; P = 1). Comparison of patients with preoperative hypertropia ≤ 15 PD revealed non-significant differences between IO myectomy and disinsertion in rate of success (100% vs 81.3%; P=0.226) and correction of primary position hypertropia (8.8±3.2 vs 7.6±4.0 PD; P=0.336).

IO myectomy has a greater effect in reduction of primary position hypertropia. However, IO disinsertion is as effective as myectomy if preoperative vertical deviation is ≤ 15 PD. Both procedures are effective in correction of AHP which is one of the main patients’ complaints and self-adjustment is observed in both operations