After synapsing in the pretectal nuclei, where do nerve fibers travel in the light pupillary pathway?

The light pupillary pathway begins when light stimulates the retina, activating photoreceptors and subsequently leading to the transmission of signals via the optic nerve. Once these signals reach the pretectal nuclei, a critical step occurs: the nerve fibers project to both the ipsilateral and contralateral Edinger-Westphal (EW) nuclei.

This bilateral projection is essential for the consensual pupillary response, allowing both pupils to constrict simultaneously when light is shone in one eye. This means that when the light signal is received in one eye, it not only affects the EW nucleus on the same side (ipsilateral) but also synapses with the EW nucleus on the opposite side (contralateral). Thus, this pathway ensures that the pupillary constriction response is coordinated and even.

The other proposed pathways do not fully capture the action of vision and pupillary response in this context. The ciliary ganglion is indeed involved in the overall process, but it does not receive direct projections from the pretectal nuclei. The optic chiasm serves the function of visual information crossover but is not directly part of the pupillary constriction pathway after synapsing in the pretectal nuclei. Therefore, the correct understanding of the pupillary