Final answer:
The ciliary ganglion is the parasympathetic ganglion where synapses occur for the pathway that innervates the eye, specifically controlling pupillary size through the contraction of the iris muscles.
Step-by-step explanation:
The parasympathetic pathway that innervates the eye synapses within the ciliary ganglion. This ganglion is part of the cranial component of the parasympathetic system, which controls various involuntary functions in the body. The Edinger-Westphal nucleus, part of the oculomotor complex in the midbrain, gives rise to preganglionic parasympathetic fibers that travel through the oculomotor nerve (cranial nerve III) and terminate in the ciliary ganglion. From here, postganglionic parasympathetic fibers project to the smooth muscle of the iris, releasing acetylcholine, which causes the muscles to contract, consequently constricting the pupil to control pupillary size.