n. the organ of sight. The human eye is a layered, globular structure whose shape is maintained by fluid filling its interior. There are three layers: (a) the outer corneoscleral coat, which includes the transparent cornea in front and continues as the fibrous sclera over the rest of the globe; (b) the middle layer, called the uveal tract, which includes the iris, the ciliary body, and the choroid layer; and (c) the innermost layer, the retina, which is sensitive to light. Retinal ganglion cells within the retina communicate with the central nervous system through the optic nerve, which leaves the retina at the optic disk. The eye has three chambers. The anterior chamber, between the cornea and the iris, and the posterior chamber, between the ciliary body, lens, and posterior aspect of the iris, are filled with a watery fluid, the aqueous humor. The anterior and posterior chambers are in continuity through the pupil. The third chamber, the vitreous body, is the large cavity between the lens and the retina filled with vitreous humor. See also eye muscles; visual system.