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
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- Why is the nystagmus in a BPPV patient rotary? What is the underlying explanation for the rotational characteristic?
