Pupil Reflex to Flickering Blue and Red Light of Up to 500 Hz Frequency

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The frequency of a flickering light of 0.1–7 Hz is known to induce greater pupil constriction compared to a non-flickering light. The pupillary light reflex (PLR) is mediated not only by rod and cone photoreceptors but also by intrinsically photosensitive retinal ganglion cells (ipRGCs). However, to the best of our knowledge, the PLR has not been studied under light conditions with a high frequency of >7 Hz and with a color other than blue light. In this study, 26 women aged 20–22 years were subjected to the 5-min dark/5-min light protocol (5 min of dark adaptation followed by 5 min of light stimulation). The PLR was measured as the mean pupil diameter during the last minute of light stimulation. The light stimulus conditions were non-flickering or flickering at 7, 100, and 500 Hz. The duty cycle was 10%. Although no significant difference was noted in the PLR between the red 100-Hz flickering light and the red non-flickering light, the blue 100-Hz flickering light induced a greater PLR when compared to the blue non-flickering light. These results imply that ipRGCs can recover their sensitivity to light during the dark period in a flickering light of up to a frequency of 100 Hz.