Simulated and natural changes in intraocular transparency selectively affect photoreceptor-specific pupil responses

The pupillary light reflex (PLR) is modulated by retinal photoreceptors and influenced by light transmission through the intraocular media (IOM). Variations in IOM transparency, due to scattering, transmittance, or yellowing, can affect visual and non-visual functions; however, their impact on photoreceptor-specific PLR remains unclear. In this study, we measured PLR responses selectively driven by Melanopsin, S-cones, and L+M cones in young adults using silent substitution and chromatic pupillometry. These pupillary measurements were correlated with individual IOM properties. Additionally, we simulated changes with external filters. Our findings indicate that the degree of scattering or transmittance impacts the cone-driven responses. Notably, increased scattering consistently slowed S-cone-driven responses across both experiments. Melanopsin-driven PLR and yellowing showed no significant effects. These results suggest that normal variations in IOM transparency modulate cone-mediated PLR dynamics but do not affect melanopsin responses, thereby contributing to individual differences in pupil behavior and potentially influencing ophthalmic and neurological assessments that rely on optical stimuli.