Association between refractive error and the intrinsically photosensitive retinal ganglion cells (ipRGC) driven pupil response in young adult humans

Intrinsically photosensitive retinal ganglion cells (ipRGCs) are a distinct subtype of ganglion cells in the mammalian retina that contain a light sensitive photopigment, melanopsin.1,2 These cells can directly detect light levels without any input from the outer retina, and act as bona fide photoreceptors in the inner retina. ipRGCs also respond to light not only directly through melanopsin, but also indirectly through synaptically mediated input from rods and cones. ipRGC cells signal environmental light, with axons projected to the midbrain to control pupil size and circadian rhythms. They also play a role in image formation, contributing to visual detection and colour and temporal processing. There is growing evidence that these cells may also play a role in refractive development of the eye.3

The photopigment melanopsin has a peak sensitivity to blue light of about 470-480 nm. Post-illumination pupil response (PIPR), a sustained pupil constriction after short wavelength light stimulation, is an indirect measure of ipRGC activity.4 This is due to prolonged and continuous firing of ipRGC cells after stimulus offset. Previous studies have shown no effect of age and refractive error upon ipRGC-driven PIPR in young adults and children.4,5 In this study
we measured the PIPR in young adults with different refractive errors using a custom-made optical system
examined the effects of melanopsin stimulation on axial length changes to hyperopic and myopic defocus in young adult emmetropic eyes