Comparison of anterior transposition and recession of the inferior oblique muscle in unilateral superior oblique paresis

Purpose: Both anterior transposition and graded recession have been shown to be effective procedures in weakening the inferior oblique muscle. Anterior transposition may work in part by converting the inferior oblique muscle from an elevator to a depressor of the globe. In theory, this would be useful in treating the inferior oblique overaction associated with superior oblique paresis. We compared inferior oblique recession and anterior transposition for the surgical correction of Knapp's class III unilateral superior oblique paresis. Methods: Four patients underwent 14 mm recession, and five underwent anterior transposition of the inferior oblique muscle for the hypertropia in superior oblique paresis. Prism cover test measurements were made in all cardinal fields of gaze and were compared before and after operation between the two groups. Results: The mean preoperative hyperdeviation in the primary position was 12 prism diopters in the recession group and 15 prism diopters in the anterior transposition group. The mean postoperative hyperdeviation was 1 prism diopter in the recession group and 3 prism diopters in the anterior transposition group. Postoperative results in the inferior oblique field of action demonstrated a mean 3 prism diopter hypertropia in the recession group and a 2 prism diopter hypotropia in the anterior transposition group. Conclusions: Anterior transposition and graded recession gave similar results in correcting the primary position hyperdeviation in Knapp's class III superior oblique paresis. Both procedures also markedly improved the hyperdeviation in the field of action of the inferior oblique muscle and superior oblique muscle. However, anterior transposition was more likely to result in postoperative hypodeviation in upgaze.