Effect of Horizontal Strabismus Surgery on the Refractive Status

Purpose: To evaluate the effects of horizontal strabismus surgery on the refractive and astigmatic status of eyes following horizontal muscle surgery using double-angle vector analysis. Materials and Methods: This was a retrospective analysis of 137 patients (250 eyes) conducted between February 1997 and October 2010 in patients who had unilateral or bilateral recession or monocular recession and/or underwent resection of horizontal muscles by a single surgeon. Refraction data were obtained at 1-2 weeks preoperative and at 4-6 weeks and 4-6 months postoperative. Surgically induced refractive changes were calculated using double-angle vector analysis. Results: The mean change in the spherical equivalent (SE) of the refraction was 0.23 +/- 0.78 D for surgically induced refractive changes at 4-6 weeks postoperative (SIRC1; p < 0.0001) and 0.14 +/- 0.85 D (p = 0.018) for surgically induced refractive changes at 4-6 months postoperative (SIRC2), indicating a small shift in the myopic direction with regression at 4-6 months. The mean amplitudes of the induced cylinders were 0.072 +/- 1.22 D (p = 0.262) in SIRC1 and 0.20 +/- 1.14 D (p = 0.012) in SIRC2, and the mean axis of the induced plus cylinder was 21.74 degrees in SIRC1, indicating a small shift in the with-the-rule direction, but no statistically significant difference from zero (p = 0.331). The changes in the surgically induced refraction over time (SIRC d), ie, 0.05 +/- 0.64 in SE (p = 0.255) and 0.09 +/- 0.65 in the cylinder (p = 0.049), were stable. There was no significant correlation between the amounts of horizontal rectus muscle recession and/or resection and the cylinder power of individual induced astigmatism at 4-6 weeks after surgery (p = 0.266) and the myopic shift (p = 0.345). Moreover, there were no significant correlations between the ages of the patients and the spherical equivalent for SIRC1 (p = 0.858) and the induced cylinder for SIRC1 (p = 0.750). Conclusion: Horizontal rectus muscle surgery tended to induce a transient, statistically significant change in the spherical equivalent of refraction, with a myopic shift that was clinically not important. Our findings did not strongly support that the astigmatism induced changes. There was no correlation between the amount of recession and/or resection and the amount of induced refractive error.