頭位性回転刺激における眼球振盈に関する研究

抄録

Functional tests of vestibular apparatus, which have recently been able to provide delicate and exact stimulus to labyrinths, have acquired a deeper significance in diagnosis. Electrophysiological or electron microscopic studies have been making clear the physiology and anatomy of labyrinths. And the study of equilibrial system of eye muscles, chiefly nystagmus, has begun to be revalued in order to view the whole equilibrial function containing the mechanism of central nerve with oculomotor system of brainstem. However, compared with the progress in the experimental or clinical studies of cochlea and semicircular canals, those of otolith organs are lagging far behind ; a lot of problems are still left to be solved, and the function of otolith organs in equilibrial physiology has not yet satisfactorily understood.
This study is to make clear the otolithic function in position changing. First, with 10 normal persons the author observed their eye movement, their nystagmus, in their position changing under weak centrifugal force by using electronystagmograph. The position changing was done by the subjects themselves keeping their eyes open and wearing Frenzel's glasses in a dark room. The apparatus based upon the positional table system, is capable of changing the tilt of the table sagittally and bitemporally and of rotating the table. On the table the subjects can be easily moved on any axis. When the subject lies in a supine position on the table, both of his labyrinths are apart from the pivot of the apparatus by about 60 cm, so that the lateral semicircular canals are kept almost vertical. Each subject is asked not only to turn both his head and body on his axis but change the position sagittally and bitemporally. In this study the acceleration of rotation is 0.5° per second per second and the rotation is suddenly stopped after the equiangular rotation at the maximal velocity of 30° per second for one minute. Care was taken to prevent the appearance of the response decline phenomenon ; in the test 5 to 10 minutes' pause was given between each rotation.
Second, the author examined the clinical cases who had lasting and directionfixed positional nystagmus under the same conditions as mentioned above, and observed how the positional nystagmus went on under centrifugal force. Then the author investigated the relation of the change in the nystagmus with the otolithic function.
The results are as follows:
1) The perrotary nystagmus in a supine position under centrifugal force during constant velocity showed the same recurrence as, or greater than, the nystagmus in acceleration. This, the author thinks, means that, besides the factor in semicircular canals, some other factor is partaking in causing the nystagmus.
2) The postrotary nystagmus in a supine position was short in duration and small in frequency. It was deduced from this that in this case the endolymph flow was very much restrained in lateral semicircular canals.
3) In a supine position the nystagmus and the sensation caused by the stimulus was almost at the threshold or below it, but the nystagmus in most cases in a lateral position during or after the rotation was comparatively distinguishable.
4) There was not found any relation between the direction in a lateral position and that of the nystagmus in position changing while the rotation continued, but there was some relation between position changing nystagmus and the direction of lateral position after the rotation was stopped. Accordingly it is considered that the slight functional difference in both otoliths is represented by the nystagmus resulting from the stimulation caused by centrifugal force to otolith organs and vestibular center of brainstem during the equiangular rotation.