Anterior horizontal rectus anatomy in children with concomitant strabismus.
BACKGROUND Anterior ciliary vessel (ACV) counts, tendon width (TW), and limbus-to-insertion distance (LID) describe vascular, structural, and positional features of the anterior horizontal rectus. Data integrating these parameters in children with concomitant strabismus remain limited. We aimed to characterize ACV counts, TW, and LID in pediatric horizontal concomitant strabismus and examine their associations with diagnosis and clinical variables. METHODS In this hospital-based cross-sectional study, 227 children undergoing primary horizontal rectus surgery were included. ACV bundles were quantified from intraoperative images, and TW and LID were measured. Esotropia-exotropia comparisons were performed within measured muscle subsets. Exploratory analyses examined associations with deviation magnitude, age, and axial length (AL), with false discovery rate (FDR) correction. Multivariable linear regression adjusted comparisons for age and AL. Logistic regression was performed in cases with complete measurements of both horizontal rectus muscles. RESULTS The mean age was 7.31 ± 3.18 years. ACV-count patterns differed between the medial rectus (MR) and lateral rectus (LR), but not by diagnosis or deviation magnitude; 59.18% of LRs had two ACV bundles. Mean TW was 9.98 ± 0.65 mm for the MR and 9.60 ± 0.64 mm for the LR. Mean LID was 5.44 ± 0.38 mm for the MR and 6.84 ± 0.40 mm for the LR. After adjustment for age and AL, the crude LR width difference between exotropia and esotropia was attenuated (P = 0.212), whereas MR insertion remained shorter in esotropia (P = 0.022). LR width showed positive associations with age (P < 0.001) and AL (P = 0.004). Narrower MR width showed nominal associations with larger exodeviations in large-angle exotropia and did not remain significant after FDR correction. In restricted logistic regression, more anterior MR insertion was associated with esotropia (P = 0.033). CONCLUSIONS In pediatric concomitant horizontal strabismus, LR ACV bundles were more frequent than traditionally described, LR width appeared influenced by age and AL, and MR LID was shorter in esotropia than in exotropia. These integrated anatomical findings provide a useful surgical anatomical reference for children and may help frame future studies of esotropia-exotropia mechanisms and postoperative response.