Pupillary Light Reflex (PLR) is a simple non invasive neurological test that can reveal a great amount of information about the neural system. We report here a novel imaging system for measuring PLR without using any restraints to limit the subject’s movements. Our system incorporates a tracking component that can locate the subject’s eye position and redirect the pupillary imaging component to follow the subject’s movement. This system can measure PLR, at a distance from the subject, with high spatial resolution (<50 µm) and temporal resolution (120 Hz).  This new PLR device can accommodate the subject’s movement, because it is well positioned to test in young children and other people who have difficulty remaining voluntarily still during tests.

Pupillary Light Reflex (PLR) describes the phenomena that the pupil size changes in response to illumination changes at the retina. Pupil size is controlled by two antagonistic muscles in the iris: the sphincter and dilator, which are modulated by the parasympathetic and sympathetic innervation to constrict and dilate, respectively. Dysfunctions in any part along the PLR pathway including the retina, optical tract, pretectal nucleus, midbrain nucleus, and ciliary ganglion may alter the normal PLR response. Pupillary response is conventionally used as a quick test for brain injury in the emergency room by flashing a medical penlight on the eyes. With the assistance of computerized quantitative measurements, PLR has emerged as a potential non invasive test for identifying various ophthalmological disorders and neurological disorders.

In a typical PLR measurement, images of the pupil are continuously acquired for a period from a few seconds to minutes while the subject’s eye is stimulated using an optical flash with a predetermined intensity, duration, and spectrum. An image processing method is then applied to calculate the pupil size (area or radius) before, during and after the optical stimulation. The obtained “pupilogram” curve describes the temporal course of pupil size changes, from which multiple PLR parameters such as constriction amplitude, latency, constriction, and recovery time can be calculated.

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