Dynamic pupillary response to positive differential of light stimulus.

Under low background illumination, the pupil responds only to an increase in light intensity by a transient constriction when the extent and rate of the increase exceed a certain values. We term this response the dynamic papillary response in order to differentiate it from the much more sluggish and much less pronounced response moiety that governs the static pupil size according to the level of light adaptation. The characteristics of the dynamic response are studied in some detail. This virtually unidirectional rate sensitivity of pupil to light renders it difficult to be subjected to frequency-response analysis even by small signal approximation. Analysis of the experimental results suggests that this transient response is a light-precipitated confluence of few consecutive hippus.