An abnormal sensation of rotary movement associated with difficulty in balance, gait, and navigation of the environment. Vertigo results from lesions or disturbances in the inner ear, 8th nerve, or vestibular nuclei and their pathways in the brain stem and cerebellum. With caloric tests, results for the two ears can be compared, so these tests are more useful clinically than are rotational, torsion swing, and lateral swing tests using stimulation with acceleration or deceleration. Artificial stimulation of the vestibular apparatus produces nystagmus, past-pointing, falling, and autonomic responses, such as sweating, vomiting, hypotension, and bradycardia. Nystagmus, the most useful response, can be monitored by observation or, more reliably, by electronystagmography, which records changes in the corneoretinal potential.
Vestibular nystagmus is a rhythmic movement of the eyes.
It has a quick and a slow component and may be rotary, vertical, or horizontal. The direction of the nystagmus is defined by the direction of the quick component because it is easier to see. The hallucination of movement of the environment is in the direction of endolymphatic flow, and the hallucination of movement of the subject is in the opposite direction. Electronystagmography electronically detects spontaneous, gaze, or positional nystagmus that might not be visually detectable. Typically, it records responses to a battery of stimuli.