Introduction: The effects of anterior transposition of the inferior oblique on elevation in adduction have been studied, but changes in objective ocular torsion have not been investigated.
Methods: A prospective study on the effect of anterior transposition of the inferior oblique on objective torsion with use of fundus photography was undertaken in 24 eyes of 13 patients. The amount of oculartorsion was determined by measuring the angle formed by a horizontal line drawn across the geometric center of the disc and a second line connecting the geometric center to the foveola.
Results: The decrease in excyclotorsion at 6 to 8 weeks after surgery was 6.9+/-5.0 degrees (34%) (p = 0.006) and 2.8+/-4.4 degrees (13%) (not significant) after 10 weeks. An overall net change of 6.2+/-4.8 degrees (33%) was obtained after anterior transposition of the inferior oblique adjacent or anterior to the inferior rectus insertion (p = 0.006). Transpositions done 1 to 3 mm behind the inferior rectus insertion showed a negligible torsional change. Torsion where inferior oblique function normalized after anterior transposition of the inferior oblique (8.5+/-2.9 degrees) was not different from control, whereas torsion where inferior oblique function recurred after surgery (15.9+/-7.2) was significantly different from control (p = 0.002). Regression analysis showed that only preoperative inferior oblique overaction and preoperative degree of torsion predicted the change in torsion after anterior transposition of the inferior oblique.
Conclusion: Anterior transposition of the inferior oblique muscle initially decreased objective excyclotorsion, but the effect decayed beyond 10 weeks. At least in the short term only anterior transposition of the inferior oblique muscle done adjacent or anterior to the inferior rectus insertion affected torsion.