Changes in ocular extorsion after horizontal muscle surgery in patients with intermittent exotropia coexisting with hypertropia and mild inferior oblique overaction.

Abstract

To investigate changes in vertical strabismus and extorsion in patients with intermittent exotropia and mild unilateral inferior oblique muscle overaction (IOOA) who underwent horizontal muscle surgery without vertical or oblique muscle surgery. The medical records of 41 patients were retrospectively analyzed. The patients were followed up for at least 6 months after surgery. Fundus photography was performed before and after surgery, and the sum of the angles of torsion in both eyes was used to measure changes in extorsion using ImageJ software. The enrolled patients were divided into two groups according to the degree of IOOA: patients with grade 1 IOOA were placed in +1 IOOA group and those with grade 2 IOOA in +2 IOOA group. The pre- and postoperative angles of horizontal and vertical strabismus and extorsion were compared between the two groups. The +1 IOOA and +2 IOOA groups included 24 and 17 patients, respectively. The angle of preoperative exotropia did not differ significantly: 25.54 ± 5.68 prism diopters (PD) and 25.65 ± 8.11 PD in the +1 IOOA and +2 IOOA groups, respectively. In the +1 IOOA and +2 IOOA groups, hypertropia was 2.67 ± 1.52 PD and 2.82 ± 1.13 PD, respectively, and extorsion angles were 7.14 ± 2.77° and 7.94 ± 2.87°, respectively. As the IOOA degree increased, the extent of hypertropia and extorsion also increased. However, there were no significant differences between the two groups. Postoperative angles of hypertropia and extorsion significantly decreased in both groups (p < 0.001) after surgery. The degree of change in hypertropia and extorsion was not significantly different between the two groups (p = 0.563 and p = 0.354, respectively). Hypertropia and extorsion improved significantly after horizontal muscle surgery in patients with mild unilateral IOOA and intermittent exotropia. There was no significant difference in the improvement in hypertropia or extorsion between IOOA grades I and II.