Effect of vestibular stimulation on pupillary size

Abstract

The action of utricular stimulation on ocular reflexes has been examined with particular attention to the effects upon autonomic outflow and intraocular muscle activity. Brisk, conjugate deviations of the eyes in response to single air puff stimulation, in both cats and monkeys, were accompanied by pupillary reactions, constriction during the fast phase of eye movement, and dilatation during the slow phase. During the nystagmus obtained in monkeys and evoked by an air jet directed at the utricle, the pupils showed initially a strong dilatation with superimposed, rapid, minor constrictions of a random frequency. After the end of stimulation and at the occurrence of a secondary nystagmus, there was a dilatation during the fast phase and constriction during the slow. As the nystagmus gradually diminished, the pupils concomitantly returned to control size and ceased to fluctuate. Prolonged stimulation gave rise to an increased stream of efferent impulses in sympathetic fibers to the eye in synchrony with pupillary dilatation while the activity of ciliary nerves showed a simultaneous decrease. However, anatomical integrity of the sympathetic connections is not a prerequisite for the presence of these pupillary reactions to vestibular stimulation since their sectioning did not change the effect. Thus, the results of these experiments substantiate the conclusion previously reached that reflex pupillary dilatation can be accomplished by pure inhibition of parasympathetic tone.