Vertical rectus surgery for Knapp class II superior oblique muscle paresis.

OBJECTIVE To evaluate the efficacy of treating Knapp class II superior oblique muscle palsy with 7-mm nasal transposition of the ipsilateral inferior rectus muscle combined with recession of the contralateral inferior rectus muscle when the primary position hypertropia is 10 prism diopters (PD) or less. METHOD A retrospective review of 8 consecutive patients with superior oblique muscle paresis who had nasal transposition of the inferior rectus muscle in the paretic eye and recession of the inferior rectus muscle in the nonparetic eye. Ocular motility, including objective and subjective torsion, were evaluated before and after surgery. RESULTS The mean (SD) preoperative hypertropia was 5 PD (1.5) and 13.1 (3.6) PD in the primary position and downgaze, respectively. After surgery the mean (SD) hypertropia was 1.25 (1.0) and 3.25 (1.3) PD in the primary position and downgaze, respectively. The mean (SD) subjective excyclotropia decreased from 6.6 degrees (1.3 degrees) preoperatively to 0.5 degrees (0.9 degrees) after surgery, and there was a mean (SD) objective decrease in the excyclotorsion of the paretic eye by 7.8 degrees (1.4 degrees). All patients were diplopic before surgery and asymptomatic after surgery. CONCLUSION Treatment with 7-mm nasal transposition of the ipsilateral inferior rectus muscle combined with recession of the contralateral inferior rectus muscle can effectively treat Knapp class II superior oblique muscle palsy when the primary position hypertropia is 10 PD or less.