Materials and Methods: This cross-sectional study involved 106 eyes from 53 subjects. Group 1 included subjects with accommodative refractive esotropia (n=19), Group 2 included subjects with convergence insufficiency-type exotropia (n=16) and age-matched controls (n=18). Ophthalmologic examination and shear wave elastography were performed to all participants. The mean stiffness values of the medial and the lateral rectus muscles were obtained. The datas compared between groups. Also, any correlation between muscle stiffness and age, gender, muscle diameter, deviation angle and near point of convergence was investigated.

Results: The mean age of all subjects was 9.5 years (range 4-18 years). The mean stiffness value of the medial rectus muscles was 6.6±2.2 kPa in Group 1, 8.9±3.5 kPa in Group 2 and 9.4±3.4 kPa in control eyes. Statistically significant lower rigidity (higher elasticity) was found in the medial rectus muscles in Group 1. The mean stifness value of the lateral rectus muscles was 7.3±3.2 kPa in Group 1, 7.8±2.4 kPa in Group 2 and 9.1±2.9 kPa in controls. No significant difference was found between groups. The deviation angle showed a significant correlation with the mean stiffness values of the medial and lateral rectus muscles.

Conclusions: Medial rectus muscles may have greater elasticity in children with accommodative esotropia compared children with convergence insuffiency and healthy controls. Future studies are needed to establish normative data. Keywords : convergence insufficiency, medial rectus muscle, lateral rectus muscle, shear wave elastography, stiffness