Dynamic characteristics of the visuo-, vestibulo- ocular system
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概要
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A pendular rotation test was carried out to investigate the dynamic characteristics of the vestibuloocular system. The purpose of. this study was as follows : (1) In normal subjects, to calculate the transfer function (TF) of the right and the left vestibulo-ocular systems. (2) In patients with a unilateral labyrinth, to calculate the TF of rightward and leftward eye movements separately, and to detect vestibular asymmetry.<BR>The subject was asked to sit a rotating chair. A sinusoidal pendular rotation was given to the subject with eyes open in the dark. Chair rotation was made as random as possible. The chair (head) and eye movements were recorded. The TF was calculated with head velocity as input and eye velocity as output. For the calculation autoregressive analysis was used. Prior to the calculation, saccadic eye movements were eliminated from the eye movements. In normal subjects, the eye velocity curve was divided into eye movements induced by the right labyrinth and those induced by the left labyrinth. In patients, the eye velocity curve was divided into rightward eye movement and leftward eye movements. The TF was calculated by using these eye movements as output. The results were displayed as Bode plots.<BR>In normal subjects, gain diagrams of the vestibuloocular system indicated frequency dependent gain enhancement from 0.01 to 2.2 Hz at the rate of 4.2 dB/decade. In the Bode plots of the right and the left vestibulo-ocular systems, the gain decreased to 5 dB at 0.1 Hz, compared with that of the vestibuloocular system.<BR>In patients, gain diagrams of the unilateral vesti-bule-ocular system were the same as the gain of the unilateral vestibulo-ocular system in normal subjects. Patients who were examined within a few months after the onset of disease, showed that the gain of eye movement toward the healthy labyrinth was low, in the frequency range from 0.01 to 0.1 Hz, compared to that in the opposite direction. In patients who were examined more than 3 months after onset, these differences of gain were not detected.