Dynamic Analysis of the Pupil with Light and Electrical Stimulation

A television pupillometer and an on-line computer were used to determine the static and dynamic characteristics of the pupillary system in the cat. The characteristics of sphincter and dilator mechanisms were measured with pulse rate modulated electrical stimuli to sympathetic and parasympathetic nerves and found to be similar to the light-driven pupillary response characteristic at high frequencies. Linear and nonlinear features of the response characteristics that were identified include retinal logarithmic operator, neural, neuromuscular, and mechanical saturation, high-frequency third-order dynamics of the motor component with a break frequency at 0.8 Hz, nonminimum phase transport delay of about 0.2 s, and response asymmetry to positive and negative steps of stimulation.