Abstract
The 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. The 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. The 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. Vestibulo-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. These 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.
Highlights
The development of objective measurements of the vestibuloocular reflex (VOR) in response to natural values of head angular acceleration – the video head impulse test [1] – has been valuable for identifying horizontal semicircular canal loss, either unilateral or bilateral
Variability of VOR gain was much greater in the vertical planes, with a more rapid drop-off in VOR gain as head velocity increased
In all three ANOVAs (Table S1 in Supplementary Material), the factor velocity was significant – at every age, there was a decrease in VOR gain as head velocity increased (Figure 6)
Summary
The development of objective measurements of the vestibuloocular reflex (VOR) in response to natural values of head angular acceleration – the video head impulse test (vHIT) [1] – has been valuable for identifying horizontal semicircular canal loss, either unilateral or bilateral. Studies with scleral search coil recordings have shown that the value of VOR gain depends on the peak head velocity: for a given subject or patient, as the peak head velocity increases, VOR gain declines [5]. For other patients, the VOR gain may appear to be normal at low head velocities, and the loss becomes clear only as the peak head velocity is increased [5]. For this reason, the value of VOR gain at just one head velocity is not an acceptable representation of vestibulo-ocular performance, so it is presently recommended that vHIT testing should include peak head velocities >150°/s [5, 7]. The values of VOR gain across a range of head velocities are needed, and the present study reports these
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