Bielschowsky’s Sign, Bielschowsky’s Test
Bielschowsky’s sign is head tilt toward the shoulder, typically toward the side contralateral to a trochlear (IV) nerve palsy. The intorsion of the unaffected eye brought about by the head tilt compensates for the double vision caused by the unopposed extorsion of the affected eye. Very occasionally, head tilt is paradoxical (i.e., toward the involved side: presumably the greater separation of images thus produced allows one of them to be ignored).
Bielschowsky’s (head tilt) test consists of the examiner tipping the patient’s head from shoulder to shoulder to see if this improves or exacerbates double vision, as will be the case when the head is respectively tilted away from or toward the affected side in a unilateral trochlear (IV) nerve lesion. The test is usually negative in a skew deviation causing vertical divergence of the eyes. This test may also be used as part of the assessment of vertical diplopia to see whether hypertropia changes with head tilt to left or right; increased hypertropia on left head tilt suggests a weak intortor of the left eye (superior rectus); increased hypertropia on right head tilt suggests a weak intortor of the right eye (superior oblique).