Why is the nystagmus in a BPPV patient rotary? What is the underlying explanation for the rotational characteristic?
Each semicircular canal directly influences a pair of extraocular muscles that move the eye approximately in the plane of that canal, regardless of the initial position of the eye in the orbit. This is the key to your question in that an abnormality or disease that directly affects one semicircular canal may produce nystagmus that rotates the globe of the eye in a plane parallell to that in which the canal lies.
In cases of posterior canal BPPV, when the posterior canal is moved into the Hallpike position (earth-vertical), the net result is to produce false excitory signals from the affected posterior canal. When excited the posterior canal sends excitory signals to the ipsilateral superior oblique eye muscle and the contraslateral inferior rectus. This causes the eye to rotate in the socket towards the down ear in the Hallpike position.
Henry P. Trahan, Au.D.
Asst. Professor of Audiology
The Arizona School of Health Sciences
5850 E. Still Circle
Mesa, AZ 85206
Dr. Trahan is a graduate of LSUHSC, Masters of Communicative Disorders. Graduate of the University of Florida, Doctor of Audiology
Assistant Professor of Audiology at the Arizona School of Health Sciences. Lead faculty for the 4 year AuD Residential program. Currently also teaching Vestibular Assessment Procedures and Balance Remediation in the ASHS AuD Distance Ed AuD program.
20 years private practice with significant involvement in assessment of vestibular disorders and vestibular rehabilitation.
Conducted numerous workshops and presentations in regards to Audiologists in private practice adding Vestibular Assessment and Vestibular Rehabilitation to their practices.