8th Cranial Nerve – Tests for the Vestibulocochlear nerve

Definition:

The use and interpretation of medical examinations to determine the integrity and adequate function of the vestibulococlear nerve (eighth cranial nerve). The cochlear portion of this nerve provides the innervation for one of the special senses: hearing.

Test procedure:

The vestibulococlear nerve is composed of two parts: 1) the vestibular portion which preoccupies itself with balance, and 2) the cochlear portion which controls hearing. Therefore, when assessing the vestibulocochlear nerve, the examiner has to test both portions of this nerve.

The cochlear portion: to assess the cochlear function of the eighth cranial nerve, instruct the patient to block one ear and with the ticking of a watch, or by lightly rubbing their fingers, the practitioner starts at the patient’s unblocked ear and slowly moves outwards, until the patient can no longer hear the sound, at which point the practitioner makes a mental note of the distance. The same procedure is repeated on the other ear.

Test findings (inc Positive & Negative results):

The cochlear portion: If there is a large discrepancy between the left and right ear or if the hearing in both ears appears reduced, proceed to performing the Rinne and Weber tests (refer to this section).

The vestibular portion: physiological nystagmus, also called oculocephalic reflexes or doll’s eye phenomena, is induced by turning the patient’s head back (in a “yes” head movement) and moving the head laterally and medially (in a “no” head movement). The normal response to the oculocephalic test is a quick movement of the eyeball in the direction of the head travel. Unilateral lesions usually result in nystagmus, ataxia, and a head tilt toward the lesion.

Considerations:

The Rinne and Webber tests are performed as a means of discriminating between a conductive and a sensorineural loss in hearing