Postrotatory Nystagmus: Modifications Observed in Experiments with Repeated Rotatory Stimulation

Abstract

1. The effect of repeated rotatory stimulation on postrotatory nystagmus was reviewed by means of electronystagmography. Stimulation was applied as in standard cupulometry and nystagmus was recorded with the eyes closed.

2. (a) The duration of the first phase of postrotatory nystagmus after an impulse of 60%sec. showed no noteworthy reduction after repeated stimulation, which favours the adoption of this intensity of stimulation in clinical practice, (b) After application of impulses of 30%sec. a remarkable reduction in the duration of nystagmus was observed in a high percentage of subjects. This reduced duration of nystagmus is restored to its initial level by further repetition of stimulation and remains fairly constant with subsequent stimulation, (c) The above mentioned results were obtained consistently, regardless of change in the direction of rotation or variations in the time interval.

3. Attention was drawn to fibrillating ocular movements—“labyrinthine fibrillation”—which were observable when there was bilateral imbalance of labyrinthine tonus, but which did not appear in typical forms of labyrinthine nystagmus. The present findings indicate that there is a transfiguration of nystagmus into a fibrillation or the latter into the former under the influence of repeated rotation. It is suggested that this transfiguration may be an explanation of the phenomenon of the reduction of duration of nystagmus. The authors attribute this transfiguration to a central mechanism.

4. The second phase of nystagmus resulting from the previous rotation was completed before the succeeding stimulus was applied when standard cupulometric methods were utilized.