How the Eye Works

Our our five senses, many of us value our vision most of all, since it is our eyes that allow us to fully view the world around us. The eye is a miraculous creation. This illustration points out many of its key parts. You've heard it said many times, and it's true: your eye does work very much like a camera, and it has similar parts. Instructions: Roll your mouse over the name of each part of the eye to highlight the illustration and get a short description.

Cornea Iris Pupil Lens Vitreous Humor Macula Retina Sciera Optic Nerve Cornea: The transparent part of the coat of the eye that coers the Iris and Pupil and admits light into interior. Iris: The opaque, muscular diaphragm surrounding the Pupil that regulates its size. The iris forms the colored portion of the eye. Pupil: The round opening in the iris through which light enters the eye. The iris controls the size of the pupil and the amount of light admitted. Lens: The transparent, nearly spherical structure between the Irus and Vitreous Humor that focuses light rays on the Retina of the eye. Vitreous Humor: A viscous, colorless material that fills the posterior chamber of the eye which is the space behind the lens. Macula: An area of dense, centrally oriented nerve fibers that appears as a spot on the Retina. This area provides for highly focused centeral vision. Retina: The sensory membrane that lines the interior of the eye and receives the image from the lens and transmits it to the brain via the Optic Nerve. Sciera: The opaque, white outer coating that encloses the eyeball, except the part covered by the Cornea. Optic Nerve: The nerve located at the back of each eye that carries visual information from the Retina to the brain.

Light coming from objects passes through the cornea, a clear protective shield in the front of your eye. Then it goes through the pupil, an adjustable opening (often called aperture) in the center of the iris, or colored part of your eye.

Behind the pupil is the lens. Muscles inside your eye control the shape of the lens, focusing it (as a camera lens does) to view objects at different distances.

The light rays pass through the dark chamber of your eyeball to the retina (in the camera, this is the film) at the back of your eye. The retina contains nerve cells that signal to your brain through the optic nerve. As your brain receives the messages, you see the object before you.

Refractive Errors

If light rays do not focus properly on your retina, you have a refractive error. Common refractive errors include myopia (near-sightedness), hyperopia (far-sightedness), astigmatism, and presbyopia. If you are near-sighted, light rays coming into your eye focus in front of the retina, causing blurry vision. Often, this results when the cornea is too steeply curved.

If you are far-sighted, light rays focus behind the retina, which also results in blurry vision. This results most often when the cornea is too flat.

In astigmatism, the cornea has an irregular curvature that produces two different focal points.

Presbyopia is simply the inability of the eye to read close up, due to aging of the natural lens of the eye.