After the n10: late oVEMP peaks in patients with unilateral vestibular loss and healthy volunteers.

The ocular vestibular evoked myogenic potential (oVEMP) is a measure of otolith function. The initial n10 peak follows a contralateral pathway from ipsilateral utricle to contralateral inferior oblique muscle. Following the n10, a series of positive and negative waves are elicited in the inferior oblique, but their characteristics and generators are unknown. This paper therefore investigated the latency, amplitude, and laterality of these late peaks in patients with hearing or vestibular loss compared to healthy volunteers. oVEMPs were elicited to bone-conducted (BC) square wave pulses and air-conducted (AC) clicks in 63 healthy volunteers, 15 patients with profound hearing loss (HL), 45 patients with unilateral vestibular loss (uVL), and 10 patients with bilateral vestibular loss (bVL). In healthy volunteers, up to 5 peaks and troughs were elicited to BC bilaterally. The first two peaks were largest, and amplitude decreased linearly thereafter. In healthy volunteers stimulated with AC clicks and patients with uVL stimulated with either stimulus, the first 2-3 oVEMP waves were significantly larger on the side opposite the healthy/stimulated ear, while the later waves were smaller and had similar amplitude bilaterally. All peaks were absent stimulating ears with no measurable vestibular function. Late peaks were elicited in patients with intact vestibular function regardless of hearing status, demonstrating the vestibular origin of all peaks. Like the clinical n10-p15 waves, the second waves followed a dominant contralateral pathway, while waves 3 onwards appear to have a separate origin and may represent bilateral projections to the extra-ocular muscles.