Adult Human Eye

Adult human eye is a hollow globe with a diameter of approximately 2.5 cm (1 in). The wall of the globe is composed of three coats. The outer coat, called the fibros funic, supplies the basic support of the eye and gives it shape. The fibrous funic is divided into the cornea, which is the transparent, exposed membrane in front of the lens, and the sciera, the firm, while coat of the eye to which is attached the muscles that move the eyeball. The middle, or vascular, coat is composed of three regions. The choroids layer is pigmented black and carries blood vessels to and from the eye. In mammals (animals eye) other than humans, it has an iridescent layer that increases the retina’s sensitivity to low-intensity light. The ciliary’s body consists of a ring-shaped muscle, which can change the lens shape, and chiliary processes to which the lens is attached. The iris, which contains an opening, the pupil, is colored and has a sphincter and a dilator muscle, called a contractile diaphragm. The innermost coat is the retina, which lies behind the lens. It contains the optic disk, or blind spot, which is the junction of nerve fibers passing to the brain. The retina also contains rods and cones, light sensitive cells. The lens is a biconcave, transparent eye structure.

The eye is composed of three membrane layers. The outer white layer, or sclera, helps the eye keep its spherical shape. The transparent part of the sclera, or cornea, is protected by conjunctiva. The middle layer, the choroids, supplies the eye with blood. The iris, which is colored, and ciliary body, which holds the lens in position, are part of this layer. The inner layer, or retina, receive light and sends nervous message to the brain by way of the optic nerve. The fovea or focal point, and blindspot are located on the inner surface. The aqueous humor, a fluid and vitreous, a jelly, fill the cavities of the eye.