Pupillary activity measured by reflected infra-red light

A simple, reliable and inexpensive device for continuously monitoring pupillary changes is described. It is an improved version of a device first suggested by L. Stark. Infra-red light is transmitted to the iris and reflected back onto the receiver. Consequently, the device is effective only if the eye is immobile. Pupillometer ouput was related linearly to measurements made directly from motion pictures of pupil mobility. Experimental data are presented which demonstrate the stable baseline and minimal noise levels of the pupillometer in a conditioning experiment using paralyzed cats.