Surgical Management of Masquerading Superior Oblique Palsy

Purpose: To compare the surgical outcomes between superior oblique (SO) palsy (SOP) and masquerading SO palsy (mSOP). Design: Retrospective comparative case series. Methods: Medical records of patients with SOP and mSOP were reviewed from 1991 to 2024. Palsy cases had maximum SO cross section in the hypertropic eye no more than 80% of that in the fellow eye, while mSOP cases had bilaterally symmetrical SO muscles on magnetic resonance imaging. Types of surgery and effect on hypertropia (HT) were compared between groups. Result: A total of 39 patients aged 38±20 (standard deviation) years had SOP and 18 aged 36±17 years had mSOP. Maximum palsied SO cross-section was 10.6±3.8mm2, significantly smaller than 18.9±4.0mm2 of the contralateral fellow (P<0.0001), but was bilaterally symmetrical in mSOP. Mean preoperative central gaze HT was similar at 14.7±9.8Δ in SOP and 11.0±6.9Δ in mSOP (P=0.2). The commonest surgery was ipsilateral inferior oblique (IO) weakening combined with contralateral inferior rectus (IR) recession, followed by ipsilateral IO weakening and contralateral IR recession. After 41±65 months follow-up in SOP and 22±41 months in mSOP, central gaze HT decreased from 14.7±9.8Δ to 1.7±4.1Δ in SOP, and from 11.0±6.9Δ to -2.9±5.4Δ in mSOP (both P<0.0001). Surgical effect was similar at 13.2±10.3Δ in SOP and 14.1±10.0Δ in mSOP. Re-operation rate was low and similar in both groups. Conclusion: Clinical characteristics and surgical effect are similar in mSOP and SOP. Conventional surgeries are comparably effective in both. This suggests that mechanism beyond SO muscle function drive head-tilt dependent cylcovertical strabismus.