Use of a visual guide to improve the quality of VOR responses evoked by high-velocity rotational stimuli.
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High-velocity rotational stimuli have the potential to improve the diagnostic capabilities of clinical rotation testing by revealing nonlinear vestibulo-ocular reflex (VOR) responses that are indicative of asymmetric vestibular function. However, eye movements evoked by high-velocity rotations often are inconsistent over time and therefore do not yield reliable diagnostic measures. This study investigated whether use of a novel "visual guide" could improve the consistency and quality of VORs obtained during testing with pulse-step-sine (PSS) stimuli providing periodic high-velocity, horizontal-plane rotations with peak velocities up to 290 deg/s. The visual guide (narrow phosphorescent line spanning 180 degrees field of view) was mounted horizontally on the rotation chair at the subject's eye level. Eight healthy human subjects were tested either in complete darkness while performing an alerting task, or while viewing the visual guide in an otherwise dark room. We found that the visual guide improved the quality of VOR responses as shown by an increased proportion of slow-phase velocity data segments retained for analysis, by a decreased variance of the processed eye velocity data, and by a reduction of outlying VOR response measures. We also found that the visual guide did not induce visual suppression because VOR gain measures were not diminished. (+info)
Vestibular function in families with inherited autosomal dominant hearing loss.
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The inner ear contains the developmentally related cochlea and peripheral vestibular labyrinth. Given the similar physiology between these two organs, hearing loss and vestibular dysfunction may be expected to occur simultaneously in individuals segregating mutations in inner ear genes. Twenty-two different genes have been discovered that when mutated lead to non-syndromic autosomal dominant hearing loss. A review of the literature indicates that families segregating mutations in 13 of these 22 genes have undergone formal clinical vestibular testing. Formal assessment revealed vestibular dysfunction in families with mutations in ten of these 13 genes. Remarkably, only families with mutations in the COCH and MYO7A genes self-report considerable vestibular challenges. Families segregating mutations in the other eight genes do not self-report significant balance problems and appear to compensate well in everyday life for vestibular deficits discovered during formal clinical vestibular assessment. An example of a family (referred to as the HL1 family) with progressive hearing loss and clinically-detected vestibular hypofunction that does not report vestibular symptoms is described in this review. Notably, one member of the HL1 family with clinically-detected vestibular hypofunction reached the summit of Mount Kilimanjaro. (+info)
The first demonstration that a subset of women with hyperemesis gravidarum has abnormalities in the vestibuloocular reflex pathway.
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The effects of cochlear implantation on vestibular function.
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OBJECTIVE: Determine the risk posed by cochlear implantation (CI) to the labyrinth. STUDY DESIGN: Prospective cohort study. SETTING: Academic tertiary referral center. PATIENTS: Thirty-six ears belonging to 35 adult CI candidates (mean age, 46 yr; range, 23-69 yr). INTERVENTION: Cochlear implantation. MAIN OUTCOME MEASURES: Vestibular function was assessed using the quantitative 3-dimensional head impulse test (qHIT), clinical head impulse test (cHIT), post-head shake nystagmus, caloric electronystagmography, vestibular-evoked myogenic potentials, dynamic visual acuity, and Dizziness Handicap Inventory. RESULTS: All 36 ears were tested using qHIT before CI, and 28 ears were tested 4 to 8 weeks after CI. qHIT showed that 1 of 28 ears had reduced function. cHIT was 44% sensitive and 94% specific for identification of severe-to-profound vestibular hypofunction confirmed by qHIT. Post-head shake nystagmus was unchanged in 11 of 11 subjects. New hyporeflexia was found in 1 of 16 electronystagmography-tested ears. Vestibular-evoked myogenic potential showed either a disappearance of response or an increase in threshold by greater than 10 dB in 5 of 16 ears. Passive dynamic visual acuity showed no change in 16 of 16 ears. Dizziness Handicap Inventory scores worsened in 3 of 28 and improved in 4 of 28 subjects. CONCLUSION: Although small, the observed rate of labyrinthine injury was comparable to that for other risks of CI. Thus, it is important to educate CI candidates regarding possible risk to balance function, particularly when CI of an "only balancing ear" is contemplated. cHIT is useful for detecting severe high-frequency vestibular hypofunction and should be part of the pre-CI physical examination. (+info)