Unilateral four muscle surgery for extra-large monocular exotropia

Introduction: Recurrent exotropia is common following surgery for monocular large angle constant sensory exotropia. Surgery is usually limited to operations on the affected eye. Simultaneous oblique weakening surgery may enhance the effect of the horizontal rectus muscles surgery by decreasing the abducting forces. We report the results of simultaneous oblique muscle weakening procedures combined with ipsilateral horizontal rectus muscle surgery constant monocular exotropia greater than 35 prism diopters (PD).

Methods: Retrospective case series of patients who underwent unilateral lateral rectus recession combined with medial rectus muscle resection and simultaneous weakening of both ipsilateral oblique muscles. Primary outcome measure was ocular alignment in primary position.

Results: Twelve eyes of 12 patients were included. The mean preoperative exotropia improved from 57.9 ± 15.1 (range 35-80; median 60 PD) to 3.3 ± 5.5 (range 0-16; median 0 PD) postoperatively (p < 0.005). Two of 3 patients with a pre-existing vertical deviation had resolution of their vertical misalignment postoperatively. At the last postoperative follow up 92% of the patients had an exodeviation of 10 PD or less (range 0-16 PD median 0 PD), and 7 (58%) measured near and distance orthotropia. Postoperative abduction measured -0.6 ± 1 (0 to -3) and adduction -0.4 ± 0.7 (0 to -2).

Conclusion: Weakening the ipsilateral oblique muscles may enhance the effect of the horizontal rectus muscles surgery by decreasing the abducting vectorial forces when operating for a large angle monocular exotropia. As an additional potential advantage, oblique muscle surgery may be used simultaneously to address associated vertical deviations.