Is Inferior Oblique Overaction Associated With Astigmatism?

Abstract

To study the relationship between inferior oblique muscle overaction and astigmatism, and to explore any change in astigmatism after surgery. This was a retrospective chart review of patients undergoing strabismus surgery. Demographic data collected included age, diagnosis, preoperative refraction, presence of inferior oblique overaction, surgery performed, and postoperative refraction. Patients were divided into three groups: those having only horizontal strabismus without inferior oblique overaction (no inferior oblique group) as a control group, those having bilateral inferior oblique overaction (bilateral inferior oblique group), and those having unilateral inferior oblique overaction (unilateral inferior oblique group). Right eyes of the bilateral inferior oblique and no inferior oblique groups were chosen for analysis, whereas the eye with inferior oblique overaction was included in the unilateral cases. Refractions were converted to power vector coordinates for comparison. Statistical analysis was performed to compare the power vectors among groups using the no inferior oblique group as controls and to explore any postoperative change in astigmatism. One hundred eighteen patients undergoing strabismus surgery were included (60 males and 58 females; mean age: 11.31 ± 10.59 years). Patients were divided into three groups: those having only horizontal strabismus without inferior oblique overaction (no inferior oblique group; 60 patients) as controls, those having bilateral inferior oblique overaction (bilateral inferior oblique group; 41 patients), and those having unilateral inferior oblique overaction (unilateral inferior oblique group; 17 patients). Preoperatively, there were no differences in astigmatism when comparing eyes with and without inferior oblique overaction. Postoperatively, both the no inferior oblique group and the bilateral inferior oblique group equally showed an increase in with-the-rule cylinder power (P = .02 and .01, respectively). Inferior oblique muscle overaction did not result in an increased prevalence of astigmatism along the axis of the overacting muscle.