Does vestibular nystagmus obey the Listing's law?

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Listing's law exists for reducing the degree of freedom of the eye movements, in order to control the movement more easily. The eye moves along the axis, which exists on the plane, Listing's plane, perpendicular to the visual axis through the center of eyeball. The eye movements during the alert state obey this law, but there is no clear evidence of this law regarding the vestibular nystagmus. The purpose of this study is to clarify the role of the listing's law on the vestibular nystagmus. For recording the eye movement non-invasively, we used the video mage analysis system developed by us. However, standard video image is consisted by 30 frames/sec. This sampling rate is not adequate to record and analyze the rapid eye movements. Therefore, we developed the four times high-speed camera, which means the sampling rate is 120 Hz. We investigated rapid eye movements using this high-speed camera and we have got some good result. However, for analyzing the rapid eye movement, even this sampling rate is still low. Then we developed much higher speed video camera. The sampling rate of this camera is 240 Hz. Using this high speed CCD camera, we can record rapid eye movements, saccade, precisely. First of all, we studied normal saccade, and found clear Listing's plane in these subjects. Finally, the caloric stimulation, iced water irrigation to the unilateral ear, is used to evoke the vestibular nystagmus, and record and analyzed these video images, which captured by thigh speed CCD camera. From this experiment, some relationship between the Listing's law and the vestibular nystagmus coming clear.