Where is the ciliary ganglion?

The ciliary ganglion (arrow 4) is an important anatomic structure in the posterior orbit because sensory innervation to the anterior eye, parasympathetic axons for the iris to control pupil constriction, and sympathetic fibers pass that innervate the iris dilators and blood vessels. Located about 1 cm in front of the annulus of Zinn, the ciliary ganglion lies interposed between the optic nerve (shown in gray in the image) and lateral rectus (arrow 9) at the lateral aspect of the ophthalmic artery with its attendant innervation from the abducens nerve. Only the parasympathetic fibers are thought to synapse in the ganglion. The input to the ciliary ganglion includes the nasociliary nerve (arrowhead 6), sympathetic fibers from the internal carotid (arrow 7), and a motor root from the inferior division of the 3rd nerve (3 in the image) that eventually innervates the inferior oblique muscle (arrow 5). The superior division of the 3rd nerve (2 in the image) supplies the superior rectus and then courses around its medial border (arrow 10 shows the course of the nerve) to supply the levator palpebrae. The inferior division of the 3rd nerve also supplies the inferior rectus (arrow 11). The ciliary ganglion provides short ciliary nerves that travel on both sides of the optic nerve (arrow 8). Despite this maze of inputs, only parasympathetic fibers synapse in the ciliary ganglion. A low power photomicrograph of a section of a dissected ciliary ganglion (number 1) shows the nerve trunks (arrows 2 that emanate from the ganglion. At higher magnification one can see ganglion cells with central nuclei (arrow 3) and prominent nucleoli.