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The Video Head Impulse Test (vHIT) is a critical diagnostic tool for assessing the function of the semicircular canals, particularly the horizontal canal. To correctly interpret results, clinicians rely on established normative data. This article explores the key norms for vHIT, ensuring accurate diagnosis of vestibular disorders such as vestibular neuritis and bilateral vestibulopathy.
Understanding vHIT norms requires familiarity with the vestibulo-ocular reflex (VOR) gain, corrective saccades, and the influence of age. Without proper knowledge of these reference values, test results can be easily misinterpreted.
The most important norm in vHIT is the VOR gain, which is the ratio of eye movement to head movement. For the horizontal canal (lateral semicircular canal), the normal gain is typically above 0.8 in young adults. Values below 0.7 are often considered pathologic. Many laboratories use a norm of 0.8 as the lower limit, though minor variations exist based on equipment and age.
In a healthy vHIT, there should be no overt (visible) corrective saccades. The presence of overt or covert saccades indicates a deficient VOR. Norms for saccades state that any refixation saccade occurring during or after the head impulse is abnormal. However, small, low-velocity saccades in older adults may be a normal finding, but must be interpreted in context.
A bilateral comparison is essential. A difference in VOR gain between the right and left ear greater than 0.15 is often considered outside the norm and suggests unilateral weakness. This interaural asymmetry is a powerful indicator of pathology such as vestibular neuritis.
Recent research emphasizes that vHIT norms are not fixed. Different systems (e.g., video-based vs. scleral coil) may produce slightly different reference values. Clinicians should rely on the internal normative database provided by their specific vHIT device, ideally validated for their population.
Furthermore, age-related decline in VOR gain is well-documented. A gain of 0.7 might be normal for an 80-year-old but abnormal for a 20-year-old. Therefore, age-stratified norms are increasingly recommended in clinical practice.
Proper interpretation of vHIT relies on robust normative data. The core norms include VOR gain above 0.8, absence of significant corrective saccades, and minimal interaural asymmetry. Always consider patient age and the specific equipment's reference range. By adhering to established norms, clinicians can accurately diagnose and manage vestibular disorders.
For further reading, consult the Barany Society guidelines on vHIT.
This page was generated by AI.
It is not a source of trustworthy medical information.
The curated page
see also: VHIT | data_analysis | index | vhit-compensation | vhit_age | vhit_conflict | vhit_research | vhit_technical