Diplopia from skew deviation in unilateral peripheral vestibular lesions.

Vertical diplopia from skew deviation is well described in brainstem lesions. The phenomenon can also result from peripheral vestibular lesions. During the past years, we have observed these ocular changes in the acute stage following unilateral vestibular neurectomy and labyrinthectomy (n = 13), as well as in series of patients suffering from idiopathic sudden unilateral peripheral vestibular or cochleo-vestibular deficit (n = 5). Diplopia from skew deviation was noted immediately following ablative vestibular procedures; in patients with idiopathic vestibular deficit, it was observed as an associated sign. In all patients, clinical evaluation revealed an acute unilateral peripheral vestibular loss, with spontaneous nystagmus toward the unaffected ear and absence of nystagmic response to caloric testing on the affected ear. Skew deviation was measured using the Hess-Weiss test, which is based on the haploscopic principle. Static visual vertical was evaluated with the original methods of vertical frame and Maddox rod techniques. Photographs were made of the ocular fundi, to measure the degree of cyclotorsion of both eyes. In our patients, we found skew deviation with hypotropia of the eye that was ipsilateral to the affected ear and conjugated cyclotorsion and tilt of the static visual vertical on the side of the affected ear. Skew deviation was the first sign to disappear within a few days; conjugated cyclotorsion and tilt of the static visual vertical persisted for weeks to months. The eye-head postural reaction, consisting of head tilt, conjugated eye cyclotorsion, skew deviation, and alteration of vertical perception directed toward the side of the lesion, is known as the Ocular Tilt Reaction (OTR). The mechanism is presumably related to a lesion of the otolithic organs and/or to changes in the afferent graviceptive pathways. In man, the OTR is often mild and unrecognized, masked by spontaneous nystagmus and marked neuro-vegetative symptoms. Our observations indicate that skew deviation, as a part of the OTR, occurs in patients with sudden peripheral vestibular lesions, whether surgical or non-surgical in origin.