DIPLOPIA FROM SKEW DEVIATION IN UNILATERAL PERIPHERAL VESTIBULAR LESIONS

Vertical diplopia from skew deviation is well described in brainstem l esions. The phenomenon can also result from peripheral vestibular lesi ons. During the past years, we have observed these ocular changes in t he acute stage following unilateral vestibular neurectomy and labyrint hectomy (n = 13), as well as in a series of patients suffering from id iopathic sudden unilateral peripheral vestibular or cochleo-vestibular deficit (n = 5). Diplopia from skew deviation was noted immediately f ollowing ablative vestibular procedures; in patients with idiopathic v estibular deficit, it was observed as an associated sign. In all patie nts, clinical evaluation revealed an acute unilateral peripheral vesti bular loss, with spontaneous nystagmus reward the unaffected ear and a bsence of nystagmic response to caloric testing on the affected ear. S kew deviation was mesured 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. Phot ographs were made of the ocular fundi, to measure the degree of cyclot orsion of both eyes. In our patients, we found skew deviation with hyp otropia of the eye that was ipsilateral to the affected ear and conjug ated cyclotorsion and tilt of the static visual vertical on the side o f the affected ear. Skew deviation was the first sign to disappear wit hin 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 th e lesion, is known as the Ocular Tilt Reaction (OTR). The mechanism is presumably related to a lesion of the otolithic organs and/or to chan ges in the afferent graviceptive pathways. In man, the OTR is often mi ld 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 vestibul ar lesions, whether surgical or non-surgical in origin.