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Anatomy of an Eye

The eye is a small but complex organ in the human body. Its orb shape is maintained by the clear jelly-like substance within called the vitreous. The eye is supported by muscles which control the movement of the eye, open and close the eyelid, turn and roll the eye. It is protected by a tough outer layer called the sclera. The sclera is typically white, but can be discolored in the presence of certain diseases.

The eyes work in conjunction with the brain. As light enters the eye, electrical signals are sent to the brain and images are formed. Each eye sees something slightly differently and, by putting the two views together, the brain forms three-dimensional images. It functions much like a camera.

The eye is regularly bathed in tears, every time we blink. Tears protect the eye, washing away dirt and dust, and killing bacteria.

The anatomy of the eye is made up of a number of parts which work together to relay information to the brain:

Cornea

The transparent, curved outer surface of the eye is the cornea. It is composed of five layers, primarily water and collagen. It lets light into the eye and covers the iris. It contains no blood vessels and remains clear when the eye is in good health.

Iris

The colored disc of the eye is the iris. It is comprised of the endothelium, the stroma, and the epithelium. The pigment in the eye determines its color, and the pigment is based on genetics. At its center is the pupil, which expands and contracts, controlling the amount of light reaching the retina.

Lens

The lens is a capsule-like bag suspended behind the iris. It focuses the light admitted via the cornea onto the retina. It changes shape to focus the vision on distant objects; this is known as accommodation. It is comprised of the lens capsule, the lens fibers, and the lens epithelium.

Retina

The back of the eye is lined by a layer of nerve tissue that contains photoreceptors; there are about 125 million rods and 6 million cones. At the center of the retina, within the macula, is the fovea, the area of sharpest vision. It captures the light reflected by the lens converting it to electrical impulses that are passed to the brain.

Macula

Within the retina, at approximately the center, is the macula. It absorbs excess light and is responsible for sharp central vision, allowing us to see fine print. It converts the light into nerve signals via the photoreceptors within the fovea at its center.

Optic Nerve

Attached to the back of the eye near the macula is the optic nerve. It relays the electrical impulses from the retina to the brain, allowing images to form. At the point of the optic nerve attachment is a blind spot. There are no retinal photoreceptors at that point and it cannot respond to the light that enters in this area.

Conjunctiva

The inside of the eyelids and the outer surface (sclera) of the eye are covered by the conjunctiva. It is a mucous membrane comprised of many small blood vessels. It produces mucous which lubricates the eye.

The eye is a finely-tuned organ and its various parts perform highly specialized functions. Good eye health is important for proper vision.

If you're interested in learning more about the eye or in ophthalmology you should consider looking into attending online colleges.

Published: 2010-01-20