Effect of Isolated Oblique Muscle Weakening Procedures on Horizontal Deviation in A- and V-pattern Exotropia.

Purpose: To evaluate the effect of isolated oblique muscle weakening on horizontal deviation in patients with A- and V-pattern exotropia.Methods: The medical records of patients who underwent bilateral oblique muscle weakening for A- and V-pattern exotropia associated oblique muscle overaction between 2011 and 2018 were reviewed. The primary outcome measures were the angle of horizontal deviation and the amount of pattern collapse.Results: Forty-three patients had A-pattern exotropia with bilateral superior oblique muscle overaction (SOOA) and underwent superior oblique (SO) weakening, while 44 patients had V-pattern exotropia with inferior oblique muscle overaction (IOOA) and underwent inferior oblique (IO) weakening. There were significant differences in exodeviation at near and distance between measurements obtained before and after oblique muscle weakening procedures (p < .05). The mean horizontal esoshift at distance was 7.9 PD in patients who underwent SO weakening and 9.5 PD in patients who underwent IO weakening. The mean postoperative collapse was 24.6 PD for A-pattern and 10.1 PD for V-pattern exotropia.Conclusion: The oblique muscle weakening procedures have secondary effects and reduce horizontal exodeviation. This study suggests that surgeons should be aware of the effects of oblique muscle weakening on horizontal deviation and pattern collapse of when planning and performing strabismus surgery.