Pupil cycle induction test: a way of evaluating the pupillary light reflex.

Abstract

The Pupil Cycle Induction Test (PCIT) described here is a simple and sensitive clinical method for the evaluation of afferent pupillary defect. It assesses the difficulty in setting up regular and sustained light-induced pupil oscillations, in contrast to methods assessing the light reflex by timing the oscillations. PCIT was applied to 186 presumably normal eyes (with normal visual acuity and normal fundi). In ten eyes, sustained oscillations could not be induced; further investigation showed that four of these eyes had altered visual-evoked response. The test was also carried out in 34 patients suffering from anterior visual pathway disorders. Sustained pupil oscillations could not be set up in 44 out of the 57 affected eyes. In the present series, significant alteration of light-induced pupil oscillations has been observed in several patterns: (1) immediate alteration; (2) delayed interruption of oscillations without spontaneous recovery, and (3) intermittent periods with oscillations of relatively small amplitude lasting more than three pupil cycles. PCIT assesses changes in light threshold for pupil response. It is suggested that delayed and transient alterations of oscillations are related to time-dependent afferent pupil defects similar to intermittent abnormalities of visual function reported in patients with diseases of the optic nerve or the chiasm.