Pupillary activity measured by reflected infra-red light.

activity measured by reflected infra-red light. PHYSIOL. BEHAV. 28(5) 851-854, 1982.-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 pupiUometer in a conditioning experiment using paralyzed cats. Pupillometer Conditioned response Pupillary behavior MEASUREMENT of pupil size has been found useful in variety of clinical and experimental situations. Static pupil-lary diameter has been measured by direct observation via an operating microscope [5] and by photography [8, 11, 19]. Pupillary motility has been measured by cinematography [10], by reflected light from the iris to a photocell outside of the eye [11, 15, 21], by direct light through the lens to a photocell within the eye [17] and by using a laser device [4]. In the latter case, the iris is scanned 50 times per second, producing a continuous representation of pupil diameter. Human pupillary size has been monitored by television [6, 7, 20] and most recently this technique has been adopted for use with animals [12]. The devices used by these researchers are somewhat complex and expensive. We sought a simple, reliable and inexpensive method to continuously monitor pupillary behavior in paralyzed cats during the acquisition or performance of a Pavlovian conditioned response. The pupillometer described here developed from the work of Lawrence Stark [14, 15, 16, 21]. It measures the area of the pupil by monitoring the amount of projected infra-red light that is reflected from the iris to a photovoltaic sensor. The DC voltage output of a circular photovoltaic sensor is proportional to the size of the iris and is, therefore, inversely proportional to the area of the pupil. Although we have not systematically studied the influence of eye color, the amount of light reflected from the iris should also be proportional to iris pigmentation. This technique may therefore be inappropriate for lightly pigmented irises. The pupillometer described in this paper is useful in preparations where one dimension of the pupil (e.g., height) is f'Lxed and the eye is motionless with respect to the recording device. Since the measurement …