Horizontal extraocular muscle insertion locations in children undergoing extraocular muscle surgery.

Background: The location of extraocular muscle (EOM) insertions is clinically relevant in ophthalmologic surgery. The spiral of Tillaux has been a reference for normal EOM insertion since the nineteenth century. Research on EOM insertions is limited and has focused on adult cadaveric eyes. In this study we investigated the location of EOM insertions in children undergoing EOM surgery.

Methods: Children who underwent EOM surgery for strabismus or anomalous head position at a large tertiary care center were consecutively identified from October 2022 to December 2023. Intraoperative measurements of medial rectus (MR) and lateral rectus (LR) insertions were compared to the spiral of Tillaux and within patient groups using one-sample and independent-samples t tests, respectively. Associations of EOM insertions with age, refraction, and axial length were evaluated with Pearson correlation.

Results: In 292 children who underwent EOM surgery, 528 previously unoperated EOM insertions were recorded. Mean insertions were closer to the limbus than expected by the spiral of Tillaux (MR, 5.21 vs 5.5 mm [P < 0.001]; LR, 6.76 vs 6.9 mm [P = 0.001]). Esotropia was associated with closer EOM insertions than exotropia (MR, P = 0.021; LR, P = 0.045). Males had farther MR insertions than females (5.33 vs 5.03 mm [P < 0.001]). Age was weakly associated with farther EOM insertions (MR, r = 0.215, P < 0.001; LR, r = 0.232, P < 0.001). Myopia was very weakly associated with farther MR insertions (r = -0.145, P = 0.024).

Conclusions: In children undergoing EOM surgery, MR and LR insertions were closer to the limbus than expected relative to the spiral of Tillaux. This finding may have implications for surgical planning and outcomes.