Refractive changes after strabismus surgery in patients with intermittent exotropia

OBJECTIVES: To evaluate the long-term refractive changes after horizontal muscle surgery in patients with intermittent exotropia and investigate the correlation between changes in the postoperative refractive error and clinical factors. METHODS: We retrospectively reviewed the clinical data of patients aged < 15 years who underwent unilateral strabismus surgery (lateral rectus recession and medial rectus resection [RR, n = 47], lateral rectus recession and medial rectus plication [RP, n = 81], or lateral rectus recession [LRc, n = 68]). Preoperative and postoperative refractive errors up to four years after surgery were recorded. A mixed model was applied to compare the refractive error between the operated and fellow eyes and identify the factors associated with postoperative refractive changes. RESULTS: The mean age at surgery was 7.5±2.4years, and girls accounted for 56.1% of the study population. There was no significant difference in the change in the spherical equivalent of refractive error between both eyes throughout the postoperative period. In contrast, the operated eyes consistently and significantly showed higher cylindrical power in with-the-rule astigmatism by 0.25D than in fellow eyes. Age, sex, and preoperative refractive error were not correlated with changes in postoperative astigmatism. Meanwhile, the type of surgery showed a significant interaction with the astigmatism changes. RP had less effect on the changes in astigmatism than RR and LRc (p = 0.001 and p = 0.022, respectively). CONCLUSIONS: Horizontal muscle surgery has no long-term effect on the change in the spherical equivalent. However, mild with-the-rule astigmatism is induced and sustained after surgery, and the type of surgery affects the postoperative change of astigmatism.