Although it has been speculated that BPPN is due to an abnormality of the utricle or posterior semicircular canal, the origin of BPPN is still controversial. In order to clarify the origin of BPPN, we carried out a three-component analysis of nystagmus, focusing on horizontal, vertical and torsional motion, using a computerized eye movement analysis system. Applying pendular rotation stimuli, we also measured three components of eye movements evoked from the vertical semicircular canals.
The eye movements observed as rotatory nystagmus under Frenzel glasses, which are characteristic of BPPN, in most of the subjects had not only torsional, but also vertical and horizontal components. The vertical component dominant over the horizontal component.
We compared two components (vertical and torsional) of BPPN with eye movements evoked from the vertical semicircular canals. In BPPN, the torsional component of the eye movement was larger than that of the vertical component. On the other hand, the vertical component of the eye movement from vertical semicircular canals was larger than that of the torsional component.
These results suggest that the pathology of BPPN is not located only in the posterior semicircular canal.