The influence of head tilt on ocular torsion in patients with superior oblique muscle palsy.

INTRODUCTION Patients with superior oblique muscle palsy often assume a compensatory head tilt to the contralateral side of the affected eye. This tilt serves to decrease the hypertropia and, in theory, might decrease the excyclotropia. METHODS A prospective investigation was undertaken of the effect of forced head tilt to the right and left on torsion and the hypertropia in patients with unilateral superior oblique muscle palsy. RESULTS Twenty patients with unilateral superior oblique muscle palsy had a mean decrease in their hypertropia of 6.4(Delta) +/- 3.9(Delta) on forced head tilt from the head-erect position toward the contralateral side (95% CI, 4.7-8.1). This finding represented a decrease of 62% of the hypertropia found in the head-erect position. The difference was significant (p < 0.001, paired t-test). The mean decrease of the excyclotropia was only 0.25 degrees +/- 0.6 degrees on contralateral head tilt, which represented 3% of the excyclotropia in the head-erect position. This difference was not significant (p < 0.06). The percent by which the hypertropia decreased from the head-erect position to that found on contralateral head tilt was significantly greater than the amount by which the excyclotropia decreased (p < 0.001). CONCLUSIONS With contralateral head tilt, patients with superior oblique muscle palsy demonstrate a significant decrease in their hypertropia but essentially no change in their excyclotropia. The compensatory head tilt they manifest appears to serve the purpose of decreasing the vertical but not the torsional misalignment.