Changes in astigmatism after horizontal muscle recession strabismus surgery: A retrospective cohort study.

Purpose The aim of this study was to evaluate the changes in astigmatism after unilateral recession of horizontal rectus muscles in pediatric patients. Methods The authors retrospectively evaluated the medical history of 52 children with esotropia or exotropia, that underwent a unilateral recession strabismus surgery. The intervention group consisted of the 52 eyes that underwent strabismus surgery, and the control group consisted of the other 52 fellow unoperated eyes of the same participants. The intervention group was divided into medial and lateral rectus muscle subgroups, and four subgroups based on the astigmatism axis preoperatively (A: with-the-rule astigmatism, B: no astigmatism, C: intermediate meridians, D: against-the-rule astigmatism). All patients were examined one day preoperatively, and then, six weeks postoperatively. Paired tests were conducted, and the significant level was set to 0.05 or was adjusted for subgroups. Results A mean difference 0.43 D of astigmatism (95% CI: 0.27, 0.59) was observed after the surgery between intervention and control group (P < 0.001). Astigmatism change (postoperative - preoperative) in subgroup A was 0.50 D (P < 0.001) and in subgroup B was 0.75 D (P < 0.001). Moreover, astigmatism changes of 0.50 D were found in both lateral (P < 0.001) and medial rectus muscle group (P = 0.002). Conclusion Strabismus surgery appears to be associated with alterations in astigmatism, and in particular increase in cylindrical power in the eyes that had with-the-rule astigmatism or no astigmatism preoperatively. Those changes should be considered when planning the operation, to avoid transforming clinically non-significant astigmatism into clinically significant.