New Clinical Applications of the oVEMP: what can the late peaks tell us?

Abstract

The ocular vestibular evoked myogenic potential (oVEMP) provides unique insight into the otolith-ocular reflex. Here, the otoliths are stimulated artificially using bone-conducted (BC) or air-conducted (AC) stimuli, which generates a negative peak of excitation in the inferior oblique muscle, called the n10, which can be measured by surface electrodes placed below the eyes. Following the n10, the waveform continues with a series of peaks and troughs. The current thesis characterised the later peaks of the oVEMP in healthy volunteers and examined how these peaks are affected in pathologies affecting the vestibular system, brainstem and cerebellum. The first experimental chapter demonstrated that all peaks of the waveform are vestibular in origin, as they are abolished in bilateral vestibular loss. The second experimental chapter showed that the amplitude and number of late peaks can be increased in central disorders such as vestibular migraine, whereas third window lesions that provide an additional pathway for energy to enter the vestibular labyrinth enhance peak amplitude but not the number of late peaks. Findings from the final experimental chapter showed that patient groups associated with greater brainstem involvement had low amplitude responses and overall fewer peaks, while patient groups with purely cerebellar involvement had normal oVEMPs and late peaks. Together these findings demonstrate that the oVEMP is an important tool in understanding how different structures can affect the otolith-ocular reflex.