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HomeTopicsHow Vision WorksEye Anatomy
Anatomy of the Human EyeThe human eye is a complex sense organ that allows us to see. In order to process information, parts of the eye receive visual cues and other parts transmit that information to our brains. While it might sound simple, the process is quite complex and can be disrupted by a number of eye disorders.
Structure of the Eye: The OrbitThe orbit helps protect the eye from injury. The orbit is comprised of the following bones:
Portions of these seven bones converge and form a pyramid-shaped socket that points toward the back of the head. It is within this socket, which is typically called the eye socket, where the actual eyeball rests. Surrounding the eye in the eye socket is a layer of fat. This layer cushions the eyeball and promotes smooth movement of the eye within the orbit.
The EyeballThe actual eyeball contains three layers:
The eyeball also contains three chambers of fluid:
The first two chambers are filled with aqueous humor, a watery fluid that provides nourishment to the interior eye structures and keeps the eyeball inflated. The vitreous chamber is filled with a thicker fluid called the vitreous humor.
Optic NerveIn addition to numerous eye blood vessels, the eye also features the optic nerve. The optic nerve runs from the back of the eyeball and through an opening in the orbit called the optic foramen. From this opening, the nerve connects to the brain to transmit visual information.
In addition to the optic nerve, the eye contains other nerves. However, most of these nerves carry non-visual information and convey messages about pain or help control motor activity in the eye.
EyelidsThe eyelids are thin folds of skin and muscle that cover the eyes. Eyelids help protect the eye from scratches, foreign objects and more and also work to lubricate the eyes.
While we are awake, eyelids carry secretions from the lacrimal (tear) glands across the eye when we blink. When we sleep, the eyelids close, helping to keep moisture on the surface of our eyes. The eyelid actually has several layers, including:
Tear GlandsThe lacrimal glands, or tear glands, help keep the eye moist. They are located under the upper eyelids and extend inward from the outer corners of the eye.
Each gland can feature as many as 12 tear ducts. These ducts flow into a sac, which drops tears onto the eye via the puncta lacrimal, a small opening at the inner corner of the eyelid. The secretions of other glands within the eye help keep the tears from evaporating when they reach the eye's surface. The Cornea, Iris, Pupil, Lens & RetinaThe cornea is the clear portion of the eye that covers the iris and the pupil. It takes up about one-sixth of the eye. The rest of the eye, known as the scleral segment, is opaque. Several nerves and eye blood vessels run through the sclera, including the optic nerve. The sclera covers the optic nerve in a sheath.
The cornea and the scleral segment come together in an area called the limbus. The limbus contains many eye blood vessels. In the center of the iris is the pupil, which looks like a black hole. Light is able to enter the eye via the pupil, which can change size to control light flow.
Directly behind the iris is the lens. The lens focuses rays of light onto the retina. The retina is light-sensitive nerve tissue that contains photosensitive cells called rods and cones, which convert light energy into electrical signals that are carried to the brain by the optic nerve. |
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