Three-dimensional analysis of per-rotational nystagmus.

BACKGROUND

Head rotation produces a vestibulo-ocular reflex (VOR). In horizontal rotation, not only lateral semicircular canals but also posterior semicircular canals are stimulated, because posterior canals cupulae are not horizontal in the sitting position. Therefore, theoretical nystagmus is horizontal and torsional. Convection of endolymph does not occur, because the centre of head rotation is a dens of the second cervical vertebra, not the center of lateral canal. Although per-rotational nystagmus is a result of VOR, whether it could be explained by the movement of cupula remains undetermined. To answer this question, we analysed per-rotational nystagmus using three-dimensional video-oculography.

OBJECTIVE

To clarify whether per-rotational nystagmus is the same as the physical movement of cupula (theoretical nystagmus).

MATERIALS AND METHODS

Five healthy human were evaluated. The participant's head was rotated (sinusoidal yaw rotation) manually (frequency, 0.33 Hz; amplitude, 60°). The experiment was performed in a dark, with the participant's eyes open. Nystagmus was recorded and converted into digital data.

RESULTS

In all participants, the direction of nystagmus was rightward on rightward rotation and leftward on leftward rotation. In all participants, nystagmus was purely horizontal.

CONCLUSIONS

Practical per-rotational nystagmus differs completely from the theoretical nystagmus. Therefore, VOR is strongly influenced by the central nervous system.