Abstract: Objective To investigate the clinical effect of inferior oblique muscle belly transposition in the small angle congenital superior oblique muscle palsy with compensatory head position. Design Retrospective cases series. Participants The 18 patients (18 eyes) who has single eye small angle congenital superior oblique muscle palsy with compensatory head position and treated in the Ophthalmology Department of Baoding Hospital of Beijing Children's Hospital from April 2019 to December 2022. Methods For the above 18 patients, give the surgery of inferior oblique muscle belly transposition. The muscle abdomen was about 10-11 mm away from the inferior oblique muscle end and was fixed 5 mm after the temporal end of the lower rectus muscle. Observe the angle of vertical strabismus at the first-eye position measured with a prism, according to the Hunter grading method inferior oblique muscle hyperactivity of sick eye, compensatory head position, the fovea-disc angle (FDA) of fundus photograph was measured using Photoshop7.0 software. Main Outcome Measures The angle of vertical strabismus, inferior oblique muscle hyperactivity, compensatory head position and FDA. Results The angle of vertical strabismus at the first-eye position at 6 months after surgery was (0.51±0.60) PD, it was significantly lower than before (5.03±0.84) PD (t=14.241, P＜0.001). In the 18 eyes, before surgery,  the oblique muscle hyperactivity was 2+ in 10 eyes, 6 eyes disappeared and 4 eyes were 1+ after surgery; before surgery the oblique muscle hyperactivity was 1+ in 8 eyes, all disappeared after surgery, which was 100% effective. Before surgery all the 18 children showed the head tilt toward the healthy eye side, disappeared after surgery in 12 patients, and the compensatory head position was significantly improved in 6 children, there’s no reverse tilt, which was 100% effective. The FDA after surgery (4.81±2.53)° decreases (3.02±0.91)° than before surgery (9.82±5.17)°. During the 6 months’ follow-up, none of the patients developed relevant complications. Conclusion Inferior oblique muscle belly transposition is safe and effective for the treatment of small angle congenital superior oblique muscle palsy, especially in patients with compensatory head position. (Ophthalmol CHN, 2024, 33: 61-65)

Key words: inferior oblique muscle belly transposition, congenital superior oblique muscle palsy