Nystagmic response to triangular wave-like rotatory stimulation.

Abstract

The subject was allowed to sit on a swivel chair with nonpolarizing electrodes placed at the outer canthus of the eyes and on the forehead and with his head tilted 30° forward in order to study the nystagmus evoked by rotatory movements of the body, accelerated and decelerated at an equal rate.The velocity of the slow component of nystagmus was increased with an increase in the velocity of rotation of the chair, and decreased as the chair was decelerated after the maximum velocity was reached. The direction of nystagmus was reversed before the chair was stopped.A theoretical formula is available by which to calculate the π/Δ for the cupula from the magnitude and duration of accelereation and the time of reversion of the direction of nystagmus on the assumption that the endolymph system within the cupula represents a damped torsion pendulum. The π/Δ for the cupula at an acceleration of stimulus of 2°/sec2, 3°/sec2, 4°/sec2, 5°/sec2, 6°/sec2, 7°/sec2, 8°/sec2 and 9°/sec2 as calculated by using the formula was 19sec, 14sec, 23sec, 31sec, 32sec, 22.5sec and 22sec respectively.A π/Δ of 16sec was obtained when the duration of postrotatory nystagmus was employed as a basis of calculation.The value for π/Δ was found to vary with different magnitudes of acceleration, even in the same subject. thus, further studies are required to refine the theoretical formula and the method of stimulation.