Impact of Target Distance, Target Size, and Visual Acuity on the Video Head Impulse Test.

The video head impulse test (vHIT) assesses the vestibulo-ocular reflex. Few have evaluated whether environmental factors or visual acuity influence the vHIT. The purpose of this study was to evaluate the influence of target distance, target size, and visual acuity on vHIT outcomes. Thirty-eight normal controls and 8 subjects with vestibular loss (VL) participated. vHIT was completed at 3 distances and with 3 target sizes. Normal controls were subdivided on the basis of visual acuity. Corrective saccade frequency, corrective saccade amplitude, and gain were tabulated. In the normal control group, there were no significant effects of target size or visual acuity for any vHIT outcome parameters; however, gain increased as target distance decreased. The VL group demonstrated higher corrective saccade frequency and amplitude and lower gain as compared with controls. In conclusion, decreasing target distance increases gain for normal controls but not subjects with VL. Preliminarily, visual acuity does not affect vHIT outcomes.

Canal plane dynamic visual acuity in superior canal dehiscence.

OBJECTIVE: 1) To characterize normal, horizontal active dynamic visual acuity (DVA) and passive canal plane head thrust DVA (htDVA) across ages to establish appropriate control data and 2) to determine whether horizontal active DVA and passive canal plane htDVA are significantly different in individuals with superior canal dehiscence syndrome (SCDS) before and after surgical repair in the acute (within 10 d) and nonacute stage (>6 wk). STUDY DESIGN: Prospective study. SETTING: Tertiary referral center PATIENTS: Patients diagnosed with SCDS (n = 32) and healthy control subjects (n = 51). INTERVENTIONS: Surgical canal plugging on a subset of patients. MAIN OUTCOME MEASURES: Static visual acuity (SVA), active horizontal DVA, and canal plane htDVA. RESULTS: Visual acuity (SVA, active DVA, and htDVA) declines with age. In SCDS, SVA and active DVA are not significantly affected in individuals after surgical canal plugging; however, htDVA in the plane of the affected canal is significantly worse after canal plugging. CONCLUSION: Age-based normative data are necessary for DVA testing. In SCDS, htDVA in the plane of the affected canal is normal before surgery but permanently reduced afterward.

Ocular versus cervical VEMPs in the diagnosis of superior semicircular canal dehiscence syndrome.

OBJECTIVES: To determine whether cervical vestibular evoked myogenic potential (cVEMP) thresholds or ocular VEMP (oVEMP) amplitudes are more sensitive and specific in the diagnosis of superior semicircular canal dehiscence syndrome (SCDS). STUDY DESIGN: Prospective case-control study. SETTING: Tertiary referral center. SUBJECTS AND METHODS: Twenty-nine patients with SCDS (mean age 48 yr; range, 31-66 yr) and 25 age-matched controls (mean age 48 yr; range, 30-66 yr). INTERVENTION(S): cVEMP and oVEMP in response to air-conducted sound. All patients underwent surgery for repair of SCDS. MAIN OUTCOME MEASURE(S): cVEMP thresholds; oVEMP n10 and peak-to-peak amplitudes. RESULTS: cVEMP threshold results showed sensitivity and specificity ranging from 80% to 100% for the diagnosis of SCDS. In contrast, oVEMP amplitudes demonstrated sensitivity and specificity greater than 90%. CONCLUSION: oVEMP amplitudes are superior to cVEMP thresholds in the diagnosis of SCDS.

Balance dysfunction and recovery after surgery for superior canal dehiscence syndrome.

OBJECTIVE: To characterize (1) the impairment and recovery of functional balance and (2) the extent of vestibular dysfunction and physiological compensation following superior canal dehiscence syndrome (SCDS) surgical repair. DESIGN: Prospective study. SETTING: Tertiary referral center. PARTICIPANTS: Thirty patients diagnosed as having SCDS. INTERVENTIONS: Surgical plugging and resurfacing of SCDS. MAIN OUTCOME MEASURES: Balance measures were assessed in 3 separate groups, each with 10 different patients: presurgery, postoperative short-term (<1 week), and postoperative long-term (≥6 weeks). Vestibular compensation and function, including qualitative head impulse tests (HITs) in all canal planes and audiometric measures, were assessed in a subgroup of 10 patients in both the postoperative short-term and long-term phases. RESULTS: Balance measures were significantly impaired immediately but not 6 weeks after SCDS repair. All patients demonstrated deficient vestibulo-ocular reflexes for HITs in the plane of the superior canal following surgical repair. Unexpectedly, spontaneous or post-head-shaking nystagmus beat ipsilesionally in most patients, whereas contrabeating nystagmus was noted only in patients with complete canal paresis (ie, positive HITs in all canal planes). There were no significant deviations in subjective visual vertical following surgical repair (P = .37). The degree of audiometric air-bone gap normalized 6 weeks after surgery. CONCLUSIONS: All patients undergoing SCDS repair should undergo a postoperative fall risk assessment. Nystagmus direction (spontaneous and post-head-shaking) seems to be a good indicator of the degree of peripheral vestibular system involvement and central compensation. These measures correlate well with the HIT.

Can vestibular-evoked myogenic potentials help differentiate Ménière disease from vestibular migraine?

OBJECTIVES: To characterize both cervical and ocular vestibular-evoked myogenic potential (cVEMP, oVEMP) responses to air-conducted sound (ACS) and midline taps in Ménière disease (MD), vestibular migraine (VM), and controls, as well as to determine if cVEMP or oVEMP responses can differentiate MD from VM. STUDY DESIGN: Prospective cohort study. SETTING: Tertiary referral center. SUBJECTS AND METHODS: Unilateral definite MD patients (n = 20), VM patients (n = 21) by modified Neuhauser criteria, and age-matched controls (n = 28). cVEMP testing used ACS (clicks), and oVEMP testing used ACS (clicks and 500-Hz tone bursts) and midline tap stimuli (reflex hammer and Mini-Shaker). Outcome parameters were cVEMP peak-to-peak amplitudes and oVEMP n10 amplitudes. RESULTS: Relative to controls, MD and VM groups both showed reduced click-evoked cVEMP (P < .001) and oVEMP (P < .001) amplitudes. Only the MD group showed reduction in tone-evoked amplitudes for oVEMP. Tone-evoked oVEMPs differentiated MD from controls (P = .001) and from VM (P = .007). The oVEMPs in response to the reflex hammer and Mini-Shaker midline taps showed no differences between groups (P > .210). CONCLUSIONS: Using these techniques, VM and MD behaved similarly on most of the VEMP test battery. A link in their pathophysiology may be responsible for these responses. The data suggest a difference in 500-Hz tone burst-evoked oVEMP responses between MD and MV as a group. However, no VEMP test that was investigated segregated individuals with MD from those with VM.

Second-side surgery in superior canal dehiscence syndrome.

OBJECTIVE: Bilateral superior canal (SC) dehiscence syndrome poses a challenge because bilateral SC dehiscence (SCD) plugging might be expected to result in oscillopsia and disability. Our aims were as follows: 1) to evaluate which symptoms prompted patients with bilateral SCD syndrome (SCDS) to seek second-side surgery, and 2) to determine the prevalence of disabling imbalance and oscillopsia after bilateral SC plugging. STUDY DESIGN: Prospective observational study. SETTING: Tertiary referral center. PATIENTS: Five patients with bilateral SCDS based on history, audiometric and physiologic testing, and computed tomographic findings. This includes all of our patients who have had second-side plugging surgery to date. INTERVENTION(S): Bilateral sequential middle fossa craniotomy and plugging of SCs. MAIN OUTCOME MEASURE(S): Cochleovestibular symptoms, cervical and ocular vestibular-evoked myogenic potential testing, dizziness handicap inventory, short-form 36 Health Survey, dynamic visual acuity testing. RESULTS: The most common symptoms prompting second-side surgery were sound- and pressure-induced vertigo and autophony. Three of the 5 patients reported that symptoms shifted to the contralateral ear immediately after plugging the first side, whereas in 2 patients, contralateral symptoms developed several years after the first SC plugging. Two of 4 patients experienced ongoing oscillopsia after bilateral SCDS surgery; however, all patients reported relief from their SCD symptoms and were glad that they had pursued bilateral surgery. CONCLUSION: In patients with bilateral SCDS, sound- and pressure-induced vertigo most commonly prompted second-side surgery. Despite some degree of oscillopsia after bilateral SCDS surgery, patients were very satisfied with second-side surgery, given their relief from other SCDS symptoms.