Human eye layer, known as the fibrous tunic, is composed of the cornea and sclera. The middle layer, known as the vascular tunic or uvea, consists of the choroid, ciliary body, pigmented epithelium and iris. The innermost is the retina, which gets its oxygenation from the blood vessels of the choroid (posteriorly) as well as the retinal vessels (anteriorly). The spaces of the eye are filled with the aqueous humour anteriorly, between the cornea and lens, and the vitreous body, a jelly-like substance, behind the lens, filling the entire posterior cavity. The aqueous humour is a clear watery fluid that is contained
Ciliary muscle parasympathetic postganglionic fibers are part of cranial nerve V (Nasociliary nerve of the trigeminal), while presynaptic parasympathetic fibers to the ciliary ganglia are from the oculomotor nerve. The postganglionic sympathetic innervation arises from the superior cervical ganglia. Presynaptic parasympathetic signals that originate in the Edinger-Westphal nucleus are carried by cranial nerve III (the oculomotor nerve) and travel through the ciliary ganglion via the postganglionic parasympathetics fibers which travel in the short ciliary nerves and supply the ciliary body and iris. Parasympathetic activation of the M3 muscarinic receptors causes ciliary muscle contraction, the effect of contraction is to decrease the diameter