Head Impulse Test / Head Thrust Test

The Head Impulse Test (HIT) is a widely used clinical assessment technique used to assess the angular vestibulo-ocular reflex (aVOR). 

Specifically, the HIT assesses horizontal semicircular canal (HSCC) and superior vestibular nerve function in response to discrete, small amplitude (~10◦), high acceleration (~3000-4000 ◦s2) rotational head impulses. 

The  patient is asked to fix his or her eyes on a target, like the examiner’s nose.

The examiner will then generate a rapid head impulse while monitoring the patient’s eyes for a corrective or compensatory saccade response.

Individuals with normal vestibular function should not generate a cascade after a head impulse. the eyes should stay fixed on the target.

People with vestibular hypofunction may generate a corrective saccade after the head is quickly rotated toward the affected pathological side and this is considered a (+) HIT.

With an intact vestibular function, vestibular nerve firing frequencies are able to increase in accordance with increasing ipsi-rotational velocities or accelerations without saturating or requiring a compensatory saccade to stabilize gaze.

aVOR function is evaluated as normal or abnormal by noting the presence (+ finding) or absence (-finding) of a compensatory saccade. 

Use of technologies such as the sclearal search coil (SSC) or high speed video in a laboratory setting has provided measurement of aVOR gain and eye movement latencies to validate the test.

Leave a Reply

Your email address will not be published. Required fields are marked *