The effect of bilateral inferior oblique myectomy surgery on the astigmatism

INTRODUCTION: The function of the inferior oblique (IO) muscle is to externally rotate, elevate, and abducts the eye. Inferior oblique myectomy (IOM) is one of the most commonly used techniques for correction of inferior oblique overactions (IOOA). Surgical strabismus procedures have been known to cause refractive changes. The change in ocular torsion is known to cause changes to the axis of astigmatism. AIM: To study the effect of bilateral inferior oblique myectomy on the axis and power of astigmatism. METHODS AND MATERIAL: Medical records of 40 patients (80 eyes) who underwent bilateral IOM have been reviewed. Both eyes spherical equivalent, cylinder power and axis preoperatively and 2 months and 6 months postoperatively were recorded and analyzed. RESULTS: The preoperative visit assessment showed that the main diagnosis of cases was exotropia in 19 (47.5%) patients, followed by esotropia in 18 (45%) patients, and Orthotropia (i.e. patients had no horizontal misalignment, only bilateral IOOA) in 3 (7.5%) of the recruited patients. The study showed that IOM has a statistically significant effect on the cylinder power of astigmatism. However, it does not contribute to a significant change in the axis of astigmatism. Yet it was noticed that the axis in each eye in the 2 months postoperative visit had moved to an opposite direction, in the right eye the axis decreased and in the left eye the axis increased indicating more intorsion, however this effect disappeared in the 6 months visit, yet all these changes were statistically insignificant. CONCLUSION: bilateral IOM leads to a statistically significant change in the cylinder power of astigmatism, with change in the axis of astigmatism towards intorsions yet statistically insignificant.