Unilateral inner ear dysfunction is a weakness on one side of the vestibular (inner ear) system. A person suffering from this type of vestibular disorder may suffer imbalance, wooziness when turning the head, and, in the early stages, vertigo or the sensation of spinning. Causes include labyrinthitis (inflammation of the inner ear), neuritis (inflammation of the acoustic nerve), or herpes zoster oticus (which specifically affects the facial and auditory nerves). An acoustic neuroma (a benign tumor of the cranial nerve), or other strategically positioned brain tumor, may also cause unilateral vestibular dysfunction.
Bilateral inner ear dysfunction is a weakness on both sides of the vestibular system. A person with bilateral vestibular dysfunction may suffer imbalance, wooziness when turning the head, and also may suffer oscillopsia, or the illusion that things are bouncing up and down. This type of dysfunction can occur with ototoxicity (toxicity to the auditory nerve) or Meniere's disease.
These arise from a combination of deficits in the vestibular, visual, and somatosensory systems. ("Somatosensory" refers to positional sensory systems within the body that help with muscle tone in the feet, legs, back and hips). Such disorders commonly affect balance, and physical therapy strategies are aimed at improving or compensating for balance loss.