Background/hypothesisThe video Head Impulse Test (vHIT) is now widely used to test the function of each of the six semicircular canals individually by measuring the eye rotation response to an abrupt head rotation in the plane of the canal. The main measure of canal adequacy is the ratio of the eye movement response to the head movement stimulus, i.e., the gain of the vestibulo-ocular reflex (VOR). However, there is a need for normative data about how VOR gain is affected by age and also by head velocity, to allow the response of any particular patient to be compared to the responses of healthy subjects in their age range. In this study, we determined for all six semicircular canals, normative values of VOR gain, for each canal across a range of head velocities, for healthy subjects in each decade of life.Study designThe VOR gain was measured for all canals across a range of head velocities for at least 10 healthy subjects in decade age bands: 10–19, 20–29, 30–39, 40–49, 50–59, 60–69, 70–79, 80–89.MethodsThe compensatory eye movement response to a small, unpredictable, abrupt head rotation (head impulse) was measured by the ICS impulse prototype system. The same operator delivered every impulse to every subject.ResultsVestibulo-ocular reflex gain decreased at high head velocities, but was largely unaffected by age into the 80- to 89-year age group. There were some small but systematic differences between the two directions of head rotation, which appear to be largely due to the fact that in this study only the right eye was measured. The results are considered in relation to recent evidence about the effect of age on VOR performance.ConclusionThese normative values allow the results of any particular patient to be compared to the values of healthy people in their age range and so allow, for example, detection of whether a patient has a bilateral vestibular loss. VOR gain, as measured directly by the eye movement response to head rotation, seems largely unaffected by aging.

Taps to the forehead on the midline, at the hairline (Fz), with a reflex hammer or powerful bone conduction vibrator caused short-latency surface potentials from beneath both eyes in all healthy subjects. The earliest negative responses were invariably absent from the eye contralateral to the side of a previous vestibular nerve section but were preserved despite sensorineural hearing loss. These responses probably reflect vestibular function via crossed otolith-ocular pathways.

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Objective: While compensatory saccades indicate vestibular loss in the conventional head impulse test paradigm (HIMP), in which the participant fixates an earth-fixed target, we investigated a complementary suppression head impulse paradigm (SHIMP), in which the participant is fixating a head-fixed target to elicit anticompensatory saccades as a sign of vestibular function.Methods: HIMP and SHIMP eye movement responses were measured with the horizontal video head impulse test in patients with unilateral vestibular loss, patients with bilateral vestibular loss, and in healthy controls.Results: Vestibulo-ocular reflex gains showed close correlation (R 2 5 0.97) with slightly lower SHIMP than HIMP gains (mean gain difference 0.06 6 0.05 SD, p , 0.001). However, the 2 paradigms produced complementary catch-up saccade patterns: HIMP elicited compensatory saccades in patients but rarely in controls, whereas SHIMP elicited large anticompensatory saccades in controls, but smaller or no saccades in bilateral vestibular loss. Unilateral vestibular loss produced covert saccades in HIMP, but later and smaller saccades in SHIMP toward the affected side. Cumulative HIMP and SHIMP saccade amplitude differentiated patients from controls with high sensitivity and specificity.Conclusions: While compensatory saccades indicate vestibular loss in conventional HIMP, anticompensatory saccades in SHIMP using a head-fixed target indicate vestibular function. SHIMP saccades usually appear later than HIMP saccades, therefore being more salient to the naked eye and facilitating vestibulo-ocular reflex gain measurements. The new paradigm is intuitive and easy to explain to patients, and the SHIMP results complement those from the standard video head impulse test. Classification of evidence:This case-control study provides Class III evidence that SHIMP accurately identifies patients with unilateral or bilateral vestibulopathies. Neurology ® 2016;87:410-418 GLOSSARY AUC 5 area under the curve; BVL 5 bilateral vestibular loss; HIMP 5 conventional head impulse paradigm; SHIMP 5 suppression head impulse paradigm; UVL 5 unilateral vestibular loss; vHIT 5 video head impulse test; VOR 5 vestibuloocular reflex.