Test retest reliability of ocular vestibular evoked myogenic potentials

Abstract

Occular Vestibular Evoked Myogenic Potentials (oVEMP) responses have been consistently obtained in healthy individuals. Reports in literature have been suggestive of their utility in evaluating patients with vestibular disorders (Iwasaki et al., 2008 & 2009). Compared to Cervical VEMPs (cVEMPS), oVEMPs are less strenuous for the subjects to perform, and symmetrical responses can be easily obtained without monitoring background activation. As the oVEMP test gains popularity and worldwide recognition as a valid and reliable test of otolith function, it is likely to supplement cVEMP in the assessment of end organ function and act as a complementary technique when assessing central vestibular disorders. However, the clinical use of any test requires the establishment of reliability of the test and little is known about the test-retest reliability of oVEMPs (Isaradisaikul, Strong, Moushey, et al., 2008; Eleftheriadou, Deftereos, Zarikas, et al., 2008). Nguyen et al., (2010) reported about the test-retest reliability of oVEMP , however, smaller number of participants, larger gap between test and retest sessions and absence of fixed reference point for upward gaze may have played spoilsport and a better control at these variables may bring about a different result. So, the present study aimed at examining the test-retest reliability of the sound-induced oVEMP parameters. Monaural contralateral oVEMPS were recorded from 30 healthy individuals with normal audio-vestibular system and the test was repeated after a minimum gap of 1 week, keeping the other parameters constant. The obtained data was analyzed using Cronbach’s alpha test. The results revealed excellent test-retest reliability for the amplitude parameters barring the asymmetry ratio, which showed fair-to-moderate reliability. The latencies also demonstrated fair-to-moderate test-retest reliability. These reliability values for oVEMP are better than those reported for cVEMP and could be attributed to a number of factors including smaller area of electrode placement making it less error prone, oVEMP being excitatory potential as opposed to cVEMP being inhibitory, and lesser fatigability of extra-occular muscles contrary to higher fatigability of the SCM muscle. The test-retest reliability values, thus, prove that the test is quite reliable and can be used clinically with confidence.