Intrinsically Photosensitive Retinal Ganglion Cells Targeted Chromatic Pupillometry Using A Ring Light Stimulus

With the discovery of the presence of the photopigment melanopsin in the intrinsically retinal ganglion cells (ipRGCs) around 20 years ago, the interest in chromatic pupillometry increased. Melanopsin, and consequently ipRGCs, have a high sensitivity to the blue light, showing a different pupil light response (PLR), especially in the pupil recovery, between the blue and red stimuli. It is also known that, although the ipRGCs are broadly spread in the retina, they do not exist in the fovea, and they are most abundant in the peri-foveal region. Chromatic pupillometry technique normally uses full-field stimulators to deliver the coloured stimuli close to the person’s eye. In this study, a novel type of stimuli using a ring light with coloured filters was studied and proposed that could allow a more targeted stimulation of the ipRGCs, reducing the quantity of light entering the retina and maximizing their effect in PLR. This ring light should be placed in a certain distance to the eye, determined with an optical simulation. Some preliminary experiments were made in one individual to assess the viability and potential interest of this type of stimulus. The Post-Illumination Pupil Light Response 6s after the stimuli offsets (PIPR-6s) is a parameter highly used in chromatic pupillometry. The difference of the PIPR-6s value between the blue and the red stimuli was 13.1%, which is aligned with the literature when using full-field stimulators. It was found that, using a ring light as stimuli at 30 cm of distant in the front of the eye, were obtained compatible results as the ones described in the literature. This work indicates a potential new way to stimulate the pupil for chromatic pupillometry, focused on a targeted stimulation of the ipRGCs, that could be used for developing new pupillometer systems more portable and accessible.