Skew deviation, or the Hertwig-Magendie sign, is a supranuclear vertical misalignment of the visual axes; the final common efferent pathway for eye movements is spared (cf. hypertropia, hypotropia, due to ocular motor nerve palsies or extraocular muscle disease). This is thought to reflect damage to otolith-ocular pathways or vestibulo-ocular pathways. There may be concurrent ocular tilt reaction. Bielschowsky’s head tilt test is usually negative (cf. ocular motor nerve palsies).
Skew deviation has been associated with posterior fossa lesions, from midbrain to medulla. Ipsiversive skew deviation (ipsilateral eye lowermost) has been associated with caudal pontomedullary lesions, whereas contraversive skew (contralateral eye lowermost) occurs with rostral pontomesencephalic lesions, indicating that skew type has localizing value.
Brandt Th, Dieterich M. Skew deviation with ocular torsion: a vestibular brainstem sign of topographic diagnostic value. Annals ofNeurology 1993; 33: 528-534