eye

the complicated organ of sight. Each eye is roughly spherical and contained within the bony orbit in the skull. The outer layer is fibrous and comprises the opaque SCLERA and transparent CORNEA . The middle layer is vascular and is made up of the choroid (the blood supply for the outer half of the retina), ciliary body (which secretes aqueous humour) and the IRIS . The inner layer is sensory, the RETINA . Between the cornea and the LENS is a chamber filled with liquid aqueous humour, and behind the lens is a much larger cavity with jelly-like vitreous humour Light enters the eye through the cornea and thence via the aqueous humour to the lens, which focuses the light on to the retina. The latter contains CONE and ROD cells that are sensitive to light, and impulses are sent to the visual cortex of the brain via the optic nerve to be interpreted.