Ocular Vestibular Evoked Myogenic Potentials Via Bone-Conducted Vibrations Applied to Various Midsagittal Cranial Sites

Objective: This study applied bone-conducted vibration (BCV) stimulation to various midsagittal sites on the cranium to optimize stimulation conditions for ocular vestibular evoked myogenic potentials (oVEMPs). Study Design: Ten healthy subjects (7 men and 3 women, aged 25-32 yr) without previous ear disorders were enrolled in this study. Each subject underwent oVEMP test using BCV applied to 4 cranial sites on the midsagittal plane, namely, the Fpz (above the glabella), Fz (the midline forehead at the hairline), Cz (vertex), and inion. In addition, the linear distances from the vestibule to the 4 sites were measured via multiplanar reconstruction of computed tomographic scans. Setting: Tertiary referral university hospital. Results: All 10 subjects showed 100% clear oVEMPs at the Fpz, Fz, inion, and Cz sites. The mean +/- SD nI latencies of these 4 sites were 8.9 +/- 0.8, 9.8 +/- 2.4, 11.2 +/- 1.5, and 14.0 +/- 2.0 milliseconds, respectively, exhibiting significant differences among the 4 sites. The median (range) nI-pI amplitudes of oVEMPs stimulated via the Fpz, Fz, inion, and Cz sites were 15.8 mu V (4.2-55.8 mu V), 9.9 mu V (3.8-29.0 mu V), 11.5 mu V (5.5-58.0 mu V), and 6.1 mu V (2.5-21.4 mu V), respectively, indicating significant differences among the 4 sites. Of them, the oVEMPs elicited by BCV mode at the Fpz represented the largest nI-pI amplitude, when compared with the other 3 sites. Furthermore, the linear distances from the vestibule to the Fpz, Fz, inion, and Cz sites were 10.7 +/- 0.4, 11.5 +/- 0.5, 8.6 +/- 0.4, and 12.0 +/- 0.5 cm, respectively. The inion site had the shortest distance to the vestibule, but it did not show the earliest nI latency. Conclusion: The Fpz may be the optimal site for BCV stimulation for screening oVEMPs in reflex magnitude.