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 non-comparative 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 pre-operative 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.