Cirtopic Effect on Steady-State Pupil Size is Time of a Day Dependent

A number of studies have been conducted to develop the mechanism and equations between pupil size and luminance [1,2]. The discovery of a new class of photosensitive cells in the retina, the intrinsically photosensitive retinal ganglion cells (ipRGCs), which send retinal information induced by ambient light to the brain center to partly control the physiological characteristics of human, in particular the pupil size, leads researchers to explore how the ipRGCs react under different luminance conditions. It is evidenced that the pupil size, an important factor of visual performance, is influenced by this cirtopic effect [3,4]. However, all past investigations of cirtopic effect on pupil size were conducted at a certain time of the day by researchers [5,6]. Whether the cirtopic effect on pupil size depends on time of a day has not been examined yet. In this study, the pupil diameters at different time of a day were measured to deduce the relationship between cirtopic effect on pupil size and time of a day.