To evaluate the correlation among hypertropia, inferior oblique overaction (IOOA), and extorsion.

Thirty-one patients with congenital unilateral superior oblique palsy were evaluated. Visual acuity tests, refraction tests, ocular movement tests, prism cover tests, and fundus photography were performed. The correlations of vertical deviation, IOOA, and extorsion were analyzed. The operation method involved weakening the inferior oblique muscle, and then a comparison was made between measurements 1 month preoperative and 1 month postoperative for vertical deviation, inferior oblique overaction, and extorsion.

On average, preoperative hypertropia was 8.84±6.88 prism diopters (PD), IOOA was 2.20±0.69, and extorsion was 18.06±5.83°. The Pearson's correlation of IOOA and extorsion, hypertropia and IOOA, and extorsion and hypertropia were r=0.620, r=0.327, and r=0.126, respectively. Postoperative hypertropia, IOOA, and extorsion were reduced to 1.42±3.11PD, 0.42±1.11, and 8.63±5.09, respectively.

Both extorsion and hypertropia showed significant positive correlations with IOOA, whereas hypertropia and extorsion revealed somewhat weaker positive correlations in congenital monocular superior oblique palsy. In addition, the amount of hypertropia was reduced, and extorsion and IOOA improved after recession of the inferior oblique muscle.