Policlinico San Pietro Introduces New Test for Balance Disorders: The Video Head Impulse Test (vHIT)

Before understanding how this test works, it is important to know the anatomical structure of the inner ear and, in particular, the role of the semicircular canals.

"The inner ear is made up of two structures: the anterior labyrinth or cochlea (which is responsible for hearing sounds and noises) and the posterior labyrinth or vestibule (the organ of balance). The vestibule, in turn, consists of five small organs:

• the saccule;
• the utricle;
• the 3 semicircular canals (anterior, lateral, posterior).

The saccule and utricle measure the acceleration with which the head moves in a straight line (forward, backward, up, down, right, left) and allow us to perceive gravity. The semicircular canals, on the other hand, measure the angular acceleration of head movements (for example, when we rotate our head to the right or left or when we tilt our head to look up or down).

The information gathered by the semicircular canals is crucial for generating precise eye movements during head movements.

For instance, if we keep our gaze fixed on a stationary object in front of us and simultaneously rotate our head quickly to the right, we continue to see the object clearly because, during the head movement to the right, our eyes gradually and precisely move to the left. This eye movement is automatic and is generated by the right semicircular canal: it is the vestibulo-ocular reflex, continues the specialist," explains Dr. Bolandrini.

Prescribed by an otolaryngologist, the vHIT is a remote camera system, meaning it does not require a facial mask.

"It consists of a special infrared camera and a connected computer. The person being examined sits approximately 90 cm from the camera and is asked to fixate on a small target placed on the wall in front of them. The operator stands behind the person and, with hands firmly placed on the head, applies small, rapid, unpredictable movements to the head.

The camera accurately records the head movement and the eye movement. A special software compares the two movements and uses specific algorithms to calculate the functioning of the semicircular canal, displaying the results as numerical and graphical values.

This system overcomes the limitations of the vestibular specialist’s eye, which in the clinical test can only detect a total deficit of the semicircular canal’s function, especially the lateral canal," explains Dr. Bolandrini.

"After a thorough anamnesis (collection of the symptoms reported by the patient) and a careful clinical examination of the vestibular function (observation of signs such as spontaneous nystagmus, nystagmus triggered by certain positions, head shaking, a tendency to fall to one side), the vHIT provides valuable information on the functioning of the semicircular canals and is therefore very useful in all types of vertigo and balance disorders, both in the acute phase and for monitoring their evolution over time.

Moreover, for the first time, it allows us to effectively study individual semicircular canals and discover dysfunctions in portions of the labyrinth present in only one ear or in both, helping to identify new types of vestibular diseases," emphasizes Dr. Bolandrini.

The vHIT is a completely non-invasive test. The head movements applied are very small and do not cause pain or vertigo. Even just 5 movements for each semicircular canal are sufficient.

The test typically lasts about 15 minutes, and the report is provided at the end of the test. Eyes should be free of makeup (mascara).

The vHIT is also suitable for cooperative children (who are able to maintain visual fixation on an object of interest) and elderly individuals. Only significant neck rigidity in certain individuals may prevent the test from being performed.