Effects of viewing distance on ocular vestibular evoked myogenic potentials (oVEMPs) for air- and bone-conducted stimuli at multiple sites

BACKGROUND: The ocular vestibular evoked myogenic potential is otolith-dependent and has been suggested to be a manifestation of the linear vestibulo-ocular reflex (L-VOR). A characteristic feature of the translational LVOR (t-LVOR) is its dependence on the distance of a target. OBJECTIVE: To assess if viewing distance affects amplitude and latency properties of the ocular vestibular evoked myogenic potential (oVEMPs). METHODS: Bone- and air-conducted (BC and AC) stimuli were used to evoke oVEMPs in 10 healthy subjects. BC stimuli consisted of impulsive accelerations applied at the mastoids, AFz, Oz and Iz. AC stimuli consisted of 500 Hz tones delivered unilaterally to each ear. Target distances of 40 cm (near), 190 cm (intermediate) and 340 cm (far) were used for all stimuli. RESULTS: The largest amplitude oVEMP was obtained from Iz and the latency for AFz was shorter than for BC stimulation at other sites. We found no significant effect of target distance on oVEMP amplitudes for any of the stimuli used. There was a small but significant effect on latency with the nearest target having a longer latency (overall 12.4 ms vs 12.0 ms for the 2 more distant sites). CONCLUSIONS: Previously reported differences between latencies and stimulus sites for midline BC stimulation were confirmed. Target distance had no significant effect on oVEMP amplitude, which suggests it is not modified like other components of the t-LVOR.