PURPOSE: To investigate the surgical outcomes of inferior oblique muscle Z myotomy in patients with inferior oblique overaction (IOOA). METHODS: A prospective study was performed in 21 patients (primary IOOA in 13 patients, secondary IOOA in 8 patients) who underwent inferior oblique muscle Z myotomy. Patients with IOOA under the degree of +2 were included. Seventy percent of Z myotomies were performed at 6 mm along the physiological path after identifying the inferior oblique muscle through an inferotemporal fornix incision. A comparison was made before the operation and 3 months postoperatively on the degree of IOOA, vertical deviation, and cyclotorsion. RESULTS: Simultaneous horizontal rectus surgery was performed with inferior oblique muscle Z myotomy because all patients had combined horizontal deviation. The mean degrees of preoperative and postoperative IOOA were +1.9 +/- 0.32 and +0.7 +/- 0.67 in the primary IOOA group and +1.83 +/- 0.41 and +0.17 +/- 0.41 in the secondary IOOA group. Six of 7 patients in the primary IOOA group showed V-pattern strabismus, which was improved in all cases after the operation. In the secondary IOOA group, changes of preoperative and postoperative hypertropia and cyclodeviation were from 7.75 +/- 6.64 prism diopters and 8.6 +/- 2.31 degrees to 1.2 +/- 3.35 prism diopters and 4.7 +/- 2.02 degrees , respectively. Inadvertent complete myotomy occurred in 1 patient due to excessive traction by an assistant during the procedure. CONCLUSION: Inferior oblique muscle Z myotomy was an effective surgical procedure in patients with primary and secondary IOOA under the degree of +2.
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