Test-Retest Reliability of oVEMP's Across Different Electrode Montages

Specific Aim: Compare the difference in the contralateral peak-to-peak N1-P1 amplitude and N1 latency between the belly tendon electrode montage with the conventional infraorbital electrode montage in otologically normal patients grouped by decade with the goal of developing normative values to use clinically.

The oVEMP is a short latency (~10 ms), negative polarity evoked myogenic potential that is recorded from the extraocular muscles. The oVEMP test is well-tolerated by patients and is simple to administer. Whereas the recording of the cVEMP to air-conducted stimuli represents a means for evaluating the function of the saccule and inferior vestibular nerve, the oVEMP in response to mechanical, and probably air conducted stimuli, is now felt to represent a method for assessing the functional integrity of the utricle and superior vestibular nerve.

The oVEMP response is recorded from beneath both the ipsilateral and contralateral eyes, but the largest response is typically seen in the contralateral recording. The contralateral utricular-ocular pathway terminates on the inferior oblique muscle, the electrical field of which can be recorded by an electrode placed at the midline of the lower lid and having the subject gaze upward (i.e. which results in the inferior oblique muscle becoming more superficial to the location of the surface electrode.

The the absolute oVEMP N1 peak-to-peak amplitude has become the most important measurement for diagnostic purposes. Typical oVEMP latencies are ~11 ms for the negative peak (N1) and ~15 ms for the following positive peak (P1) .

Variables that may confound recording oVEMPs include body position and electrode montages. Regarding electrode placement, there are three different electrode montages that have been studied and implemented clinically. The vast majority of clinics favor the electrode montage reported in the early papers describing the oVEMP. The authors reported that the non-inverting electrode was placed infraorbitally at the margin of the lower eyelid. The inverting electrode was placed 2 cm inferior to the location of the non-inverting electrode. Two additional electrode montages that have been reported include: 1) the noninverting electrodes placed at the margin of the lower eyelid slightly lateral to midline and the inverting electrode placed rostral to the inner canthus of the eye, and, 2) the noninverting electrodes placed at the middle of the lmargin of the lower eyelid and a single common inverting electrode placed on the chin. A report by Sandhu et al. (2013) indicated that the maximal oVEMP amplitude was recorded with the former electrode montage. In this montage, the inverting electrode is placed over a tendon, which is believed to be (relatively) electrically neutral.