Huvudimpulstest

Huvudimpulstest, or head impulse test (HIT), is a bedside oculomotor examination used to assess the integrity of the vestibulo-ocular reflex (VOR). The VOR is a reflex that helps stabilize vision during head movement by producing an eye movement equal and opposite to the head movement. This reflex is crucial for maintaining clear vision while moving.

To perform the test, the examiner gently holds the patient's head and instructs them to fixate on a target, typically the examiner's nose or a point on the wall. The examiner then rapidly and unpredictably rotates the patient's head a small amount in the horizontal or vertical plane. The examiner observes the patient's eyes during this brief head movement.

If the VOR is functioning normally, the patient's eyes will remain fixed on the target, even though their head is moving. This is achieved by the eyes moving in the opposite direction of the head turn at the same speed. If the VOR is impaired, the eyes will not be able to keep up with the head movement, and the patient will have to make a corrective saccade (a rapid, jerky eye movement) to re-fixate on the target once the head movement stops. This corrective saccade is the key finding in a positive head impulse test.

The test can be performed passively by the examiner or actively by the patient. The passive version is more commonly used clinically. The vestibulo-ocular reflex can be tested in the horizontal, anterior, and posterior semicircular canals, corresponding to rotations in yaw, pitch, and roll, respectively. A positive head impulse test suggests a peripheral vestibular deficit, meaning there is a problem with the inner ear's vestibular organs, such as the vestibular nerve or the semicircular canals. It is a quick, non-invasive, and highly sensitive test for detecting vestibular dysfunction, particularly in cases of acute vestibular syndrome like vestibular neuritis or labyrinthitis.