Choroid Choroid The choroid, also known as the choroidea or choroid coat, is the vascular layer of the eye, containing connective tissues, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye (at 0.2 mm), while in the outlying areas it narrows to 0.1 mm. The choroid provides oxygen and nourishment to the outer layers of the retina. Along with the ciliary body and iris, the choroid forms the uveal tract. The structure of the choroid is generally divided into four layers (classified in order of furthest away from the
Parasympathetic root of ciliary ganglion short ciliary nerves. These nerves enter the posterior aspect of the eyeball to innervate the sphincter pupillae and ciliaris muscles. The "sphincter pupillae" constricts the iris. The "ciliaris" muscle changes the shape of the lens, allowing the eye to focus on nearby objects (accommodation). Neither of these muscles is under voluntary control. Parasympathetic root of ciliary ganglion The parasympathetic root of ciliary ganglion provides parasympathetic innervation to the ciliary ganglion. The ciliary ganglion is a "parasympathetic" ganglion. Incoming parasympathetic nerve fibers form synapses with the dendrites of nerve cells within the ganglion. However, the ciliary ganglion is not simply a