An assessment of the usefulness of the POLWROCHROM pupillometer to study the pupil light reflex to chromatic stimuli taking into account the intrinsically photosensitive retinal ganglion cells activity

Introduction
The pupillary light reflex is a useful diagnostic tool used to assess the function of the eye and the visual system. The increased interest in testing the pupillary light reflex is the discovery that the intrinsically photosensitive retinal ganglion cells are involved in the reflex physiology. The aim of this study was to evaluate the usefulness of POLWROCHROM pupillometer, developed at the Wroclaw University of Technology, to study the pupillary light reflex to chromatic stimuli taking into account the photosensitive retinal ganglion cells activity.

Material and methods
The pupillary light reflex to 10 sec. light pulse were recorded. In the experiment, a long wavelength (640 nm bandwidth) red light and a short wavelength (470 nm bandwidth) blue light were used at 2 different light luminance levels (10 cd/m2 and 100 cd/m2).

Results
The greatest pupil response is obtained for short wavelength (blue) light at a high luminance level, whereas the markedly lower pupil response was obtained for long (red) wavelength light at a low luminance level.

Conclusions
The observed sensitivity of the pupillary light reflex response to color and intensity of the light stimulus was similar to known from literature the results of in vitro photosensitive retinal ganglion cells electrophysiological activity study. The described system and measurement technique can provide a new tool in testing the pupillary light reflex to chromatic stimuli enabling the assessment of photosensitive retinal ganglion cells activity and identification of pupillary light reflex components derived from photoreceptors and ganglion cells, and therefore may become a clinical pupil test which allows differentiation between disorders affecting photoreceptors and those affecting retinal ganglion cells.