PubMed · 9226050
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G M Halmagyi, R A Yavor, L A McGarvie. 1997. Testing the vestibulo-ocular reflex.. https://doi.org/10.1159/000059042
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Auditory brainstem response (ABR) is the reference screening technique for acoustic neuromas, but because of a few false negatives and the increasing performance of magnetic resonance imaging (MRI), its role as the standard method has been questioned. We assessed sensitivity of screening tests in 89 patients with surgically proven acoustic neuromas. Sensitivity of ABR was 92%; 94% for extracanalicular neuromas and 77% for intracanalicular neuromas. For stapedius reflex (SR), sensitivity was 84% and for caloric vestibular response (CVR) 86%. The combined sensitivity of ABR + SR was 97% and of ABR + RS + CVR 98%. For false negatives, the greatest diameter including the intracanalicular portion was always less than 18 mm, with a mean of 15 mm, and none of these tumours reached the brainstem. For patients with unilateral cochleo-vestibular deficit, we propose ABR and SR as first-line screening tests. These tests are repeated at 6 months and at 1 year in the case of normal results. MRI is ordered for patients whose auditory threshold is too low and for those whose ABR or SR results favour retrocochlear disease.
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The realisation of combined movements of the head and eyes requires the capacity to modulate the vestibulo-ocular reflex (VOR) but the absence of sufficiently rapid visual feed back results in an open loop function. This reflex must be modulated by other mechanisms. Two options are discussed. A modulation of the gain of the reflex loop is not satisfactory for small combined movements of the head and eyes as it would no longer permit the effective compensation for unexpected perturbations of movement of the head. An additive mechanism modifying the VOR through the addition of an other ocular movement is limited by the constrictions of latency, speed and amplitude of such movement. According to experimental conditions, varying complementary effect of the two mechanisms seems to result in maximum efficiency. This paper attempts to include the mechanism of the ocular fixation index (OFI) among the models of study. The OFI applied to a pendular test is, by the nature of its stimulus, more physiologic and more capable of being integrated into existing models. In the usual conditions of the test, the additive model is probably dominant with a preponderant role in the ocular pursuit system. But whatever may be the part of each mechanism, the OFI is not only dependent on the integrity of the floccular inhibition of the VOR but on the numerous cortical and subcortical structures involved in the realisation of voluntary ocular movements. This information should encourage clinicians to investigate the ocular movements of patients presenting vertigo, particularly those with visual instability on head movements.