[Clinical characteristics and surgical outcomes in pediatric progressive restrictive strabismus]

Objective: To investigate the clinical features, imaging manifestations, histopathological characteristics, and surgical outcomes in pediatric progressive restrictive strabismus. Methods: A retrospective case series study was conducted, including data from 9 cases (9 eyes) of pediatric progressive restrictive strabismus treated at Tianjin Eye Hospital from June 2017 to October 2022. The study compared the degree of globe protrusion in both eyes, changes in eyelid fissure height during internal and external rotation in the primary gaze, summarized clinical characteristics, and analyzed intraoperative conditions, surgical outcomes and postoperative histopathological results of strabismus correction surgery. Statistical analysis was performed using Wilcoxon signed-rank test and Friedman two-way analysis of variance. Results: All 9 cases involved unilateral onset, with 4 males and 5 females. Three cases affected the right eye, and six affected the left eye. Onset age ranged from 2 to 40 months. The degree of globe protrusion in the affected eyes was 13.00 (12.00, 13.00) mm for the right eye and 12.00 (12.00, 13.50) mm for the left eye, with no statistically significant difference (Z=-1.00, P=0.317). There were no significant changes in eyelid fissure height during internal rotation [8.00 (7.25, 8.00) mm], primary gaze [7.50 (7.00, 8.00) mm], and external rotation [8.00 (7.75, 8.00) mm] in the affected eyes (χ²=1.00, P=0.607). No apparent abnormalities were observed in head CT or MRI scans, serum, or immunological tests. However, orbital CT or MRI scans indicated thickening of different extraocular muscle bellies. Six out of nine cases underwent strabismus correction surgery, and postoperative examination revealed restriction in eye movement despite achieving orthophoria in the primary gaze. Tissue pathology of three cases showed increased collagen fiber proliferation in one, scattered bundles of smooth muscle fibers amid diffuse collagen fiber proliferation in another, and abnormal proliferation of striated muscle fibers with varying diameters, increased paired box (PAX)7-positive satellite cells expressing slow muscle myosin in the third case. Conclusions: Pediatric progressive restrictive strabismus presents with restrictive changes, without significant alterations in globe protrusion and eyelid fissure height. Imaging examinations reveal thickening of the extraocular muscle bellies in the affected eye. Although strabismus correction surgery improves eye position, postoperative eye movement remains restricted. Histopathological findings in some cases show abnormal proliferation of skeletal muscle fibers or collagen fibers.