Effects of eye position on the vestibular evoked myogenic potential.
CONCLUSIONS
The position of a subject's eyes during vestibular evoked myogenic potential (VEMP) recording significantly alters the magnitude of the response. This change is largely due to an alteration in the tonicity of the sternocleidomastoid muscle (SCM) caused by variations in the position of the eye. However, even if electromyographic (EMG) normalization is conducted effects of eye position remain.


OBJECTIVE
To determine if eye position has a significant effect on the magnitude of the VEMP.


METHODS
VEMPs were collected from 32 ears measured on 16 healthy subjects. The recordings were made unilaterally using the head turn method. The acoustic stimuli were 500 Hz air-conduction short tone bursts. VEMPs were measured in three recording conditions: (i) eyes in the same direction as head turn, (ii) eyes straight ahead, (iii) eyes in the opposite direction to head turn.


RESULTS
All 32 ears tested showed a VEMP response with eyes in all three positions. Repeated measures analysis of variance (RM-ANOVA) verified an overall significant effect of eye position (p<0.001). Post hoc paired t tests revealed statistically significant differences between the eyes opposite and the other two conditions (p<0.001). Normalization of the VEMP magnitude using pre-stimulus EMG reduced the effect; however, some variability remained.
Sandhu
J S
JS
Department of Audiology, Royal Sussex County Hospital, Brighton, UK. jas.sandhu@bsuh.nhs.uk
Bell
S L
SL
D000161:Acoustic Stimulation; D000328:Adult; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D019416:Head Movements; D006801:Humans; D008297:Male; D009129:Muscle Tonus / Q000502:physiology; D009334:Neck Muscles / Q000294:innervation*; D012016:Reference Values; D014724:Vestibular Function Tests / Q000379:methods*; D055815:Young Adult