Bielschowsky head-tilt test--II. Quantitative mechanics of the Bielschowsky head-tilt test.

In ten recent cases of superior oblique (SO) palsy the involved eye elevated by 8.2 +/- 3.8 deg (standard deviation) on 45 deg ipsilateral head tilt. A computer model predicted a rise to only 4.1 deg but could easily achieve 8.2 deg by including reactions in the other cyclovertical muscles, notably on overaction of the superior rectus (SR). In 17 older cases the elevation on tilt rose to an average of 15 deg. The model shows that these deviations must be due to SR overaction. The analysis suggests that SR overaction is the main cause of the rapid increase in eye elevation in recent cases and further increases in older cases.