One- vs Two- vertical muscle surgery in the management of unilateral superior oblique muscle palsy with hypertropia over 20 PD.

To compare the surgical outcomes of One- versus Two-vertical muscle surgery in patients with unilateral superior oblique muscle palsy (SOP) with primary position hypertropia (HT) over 20 PD. Patients in Group 1 underwent inferior oblique anterior transposition plus resection (IOATR), while patients in Group 2 underwent inferior oblique anterior transposition (IOAT) along with contralateral inferior rectus (IR) recession. Medical data of all SOP patients treated by either procedure from 2000 to 2023 in our strabismus center were recruited. We compared surgical outcomes between Group 1 and Group 2 by analyzing HT correction, rate of under-correction, and over-correction. The study included 33 patients in Group 1 and 23 in Group 2. Both groups were similar in age, sex, etiology, affected side, diplopia, and head tilt. Group 2 achieved higher HT correction in all measured gazes. Group 1 had a higher risk of under-correction (18.18% in Group 1 vs 8.69% in Group 2) while Group 2 had a higher rate of over-correction (21.73% vs 0% in Group 1). In patients with severe unilateral SOP, Two-vertical muscle surgery achieved higher amounts of HT correction in all gazes despite a significantly higher risk of over-correction.