[Preliminary observations of extraocular muscle changes in patients with intermittent exotropia during binocular convergence based on MRI].

Objective: To investigate changes in diffusion-weighted imaging (DWI) of extraocular muscles in patients with intermittent exotropia (IXT) during binocular convergence using MRI, and to explore the imaging characteristics of extraocular muscle alterations in IXT. Methods: It was a cross-sectional study. Patients diagnosed with IXT at the First Affiliated Hospital of Anhui Medical University from January 2023 to September 2023 were enrolled as the IXT group, with age-and sex-matched healthy individuals recruited as the control group. Axial MRI scanning was used to measure DWI signal intensity values of the medial rectus, lateral rectus, and optic nerve during primary gaze and convergence gaze. The normalized DWI values between the two groups and two gaze conditions were compared. The correlation between normalized DWI value changes and the degree of strabismus in the IXT group was analyzed. Normally distributed data were analyzed using independent and paired t-tests, while non-normally distributed data were evaluated with Mann-Whitney and Wilcoxon signed-rank tests. Pearson correlation analysis was used to assess the relationship between DWI values and the degree of strabismus. Results: Eleven patients (22 eyes) were included in the IXT group (six males, five females; mean age, 24±4 years), and 10 healthy controls (20 eyes) were included (four males, six females; mean age, 24±1 years). Baseline characteristics were comparable between groups (P>0.05). In the control group, the normalized DWI value of the medial rectus was 0.86 (0.72, 0.97) during primary gaze and 0.97 (0.87, 1.20) during convergence gaze, with a significant difference (P<0.05). In the IXT group, the normalized DWI value of the medial rectus was 0.77 (0.72, 0.93) during primary gaze and 0.81 (0.69, 1.08) during convergence gaze, with no significant difference (P>0.05). A negative correlation trend was observed between changes in normalized DWI values of the medial rectus during convergence gaze and the degree of strabismus in the IXT group (r=-0.58, P=0.059). Conclusion: Patients with IXT exhibit significantly reduced changes in normalized DWI values of the medial rectus during binocular convergence compared to healthy controls.