Ocular Vestibular-Evoked Myogenic Potentials (VEMPs)
McCaslin and Piker (2011) report in the mid-1990s multiple investigators observed neurons within the otolith organs (saccule and utricle) of cats that were activated by loud, low-frequency stimulation. Based on this observation researchers attempted to use acoustic stimulation to measure the vestibular system in humans. In the early and mid-1990s, it was realized that the otolith organs of humans could be activated with sound and importantly, the saccule had specific projections to the sternocleidomastoid (SCM) muscle. It was reasoned that the VEMP recorded at the SCM (aka "cervical-VEMP" or "cVEMP") was generated by the saccule, thereby facilitating a simple way to evaluate the saccule and the inferior vestibular nerve (note, bi-thermal caloric ENG/VNG stimulates the horizontal canal and reflects the superior vestibular nerve). The cVEMP is useful as it is usually presents in patients with severe sensorineural hearing loss (SNHL) and intact vestibular systems, yet absent in patients who have undergone vestibular nerve section (VNS).
VEMPs recorded from under the eyes (aka "ocular-VEMP" or "oVEMP") were introduced in 2007 (see McCaslin and Piker). The oVEMP was present despite profound hearing loss in patients with normal vestibular systems and absent in patients with normal hearing who have undergone VNS.
McCaslin and Piker report that the stimulus used to evoke the cVEMP and the oVEMP can be the same; 500 Hz toneburst at 95 dbHL. However, for analysis, amplification of the cVEMP is often 5000X, while amplification of the oVEMP is often 100,000X. The peripheral origin of the air conduction oVEMP remains controversial. Nonetheless, studies have indicated air conduction-based oVEMPs likely measure a different part of the vestibular system than the cVEMP. McCaslin and Piker suggest oVEMPs may reflect the utricle and the superior vestibular nerve – similar to caloric testing.
For More Information, References, and Recommendations
Janky KL, Shepard N. (2009) Vestibular-Evoked Myogenic Potential Testing: Normative Threshold Response Curves and Effects of Age. Journal of the American Academy of Audiology (20)8:514-522.
McCaslin DL, Piker AG. (2011) Ocular Vestibular-Evoked Myogenic Potentials. Audiology Today 23(5):28-34.
Wang C-T, Huang T-W, Kuo S-W, Cheng P-W. (2009) Correlation Between Audiovestibular Function Tests and Hearing Outcomes in Severe to Profound Sudden Sensorineural Hearing Loss. Ear & Hearing 30(1):110-114.