When is isolated inferior oblique muscle surgery an appropriate treatment for superior oblique palsy?

Purpose: To evaluate the efficacy of isolated inferior oblique muscle weakening in the treatment of superior oblique palsy.
Methods: Forty-seven patients with superior oblique palsy underwent either single-muscle surgery (anteriorization or recession of the inferior oblique muscle) or two-muscle surgery (anteriorization of the inferior oblique muscle combined with recession of the contralateral inferior rectus muscle according to the amount of vertical deviation). In a retrospective noncomparative study the objective surgical effect was calculated as the difference between the deviation at the day before surgery and the deviations 6 weeks and at least 1 year after surgery. Pre- and postoperative sensorimotor status and subjective outcome were evaluated.
Results: In patients who underwent isolated inferior oblique muscle surgery the mean preoperative vertical deviation decreased from 15+/-9 (distance)/16+/-10 (near) prism diopters (PD) (anteriorization) and 7+/-5 (distance)/9+/-8 (near) PD (recession) to 4+/-4 (distance)/4+/-6 (near) PD (anteriorization) and 2+/-2 (distance)/2+/-3 (near) PD (recession) at the 1-year follow-up. In patients who underwent two-muscle surgery the mean vertical deviation decreased from 20+/-11 (distance)/21+/-10 (near) PD preoperatively and 6+/-7 (distance)/6+/-6 (near) PD at 1-year follow-up. Subjective assessment showed excellent scores among the patients treated with single-muscle surgery and slightly lower but also favorable scores among the patients treated with combined techniques. A direct comparison of the different outcome scores was not possible because of the more difficult initial situation in patients who underwent combined surgery.
Conclusions: Isolated inferior oblique muscle weakening is an effective treatment option for superior oblique palsy up to 15 PD of vertical deviation in primary position. Two-muscle surgery should be reserved for patients with larger vertical deviations.