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Introduction to the Eye

The eyes are wonderful sensory organs. They help people learn about the world in which they live. Eyes see all sorts of things - big or small, near or far, smooth or textured, colors and dimensions. The eyes have many parts - all of which must function in order to see properly.

Inside the Eye

In addition to the many sections of the eyeball itself, muscles are attached to the outer walls of the eyeball. The eye muscles are attached to the eyes in order that we can move our eyes. The interactive diagram shows these main parts. If anything goes wrong, such as from diabetic eye disease, an individual might not be able to see as well.

A Complete Picture

Visual information from the retina travels from the eye to the brain via the optic nerve. Because eyes see from slightly different positions, the brain must mix the two images it receives to get a complete picture.

What we think of as seeing is the result of a series of events that occur between the eye, the brain, and the outside world. Light reflected from an object passes through the cornea of the eye, moves through the lens which focuses it, and then reaches the retina at the very back where it meets with a thin layer of color-sensitive cells called the rods and cones. Because the light criss-crosses while going through the cornea, the retina "sees" the image upside down. The brain then "reads" the image right-side up.

 

Glossary

Aqueous Humor: a clear, watery fluid that fills the front part of the eye between the cornea, lens and iris.

Choroid: the middle layer of the eyeball which contains veins and arteries that furnish nourishment to the eye, especially the retina.

Conjunctiva: a mucous membrane that lines the eyelids and covers the front part of the eyeball.

Cornea: the transparent outer portion of the eyeball that transmits light to the retina.

Fovea: A tiny spot located in the macula that is the area of clearest vision on the retina.

Iris: the colored, circular part of the eye in front of the lens. It controls the size of the pupil.

Lens: the transparent disc in the middle of the eye behind the pupil that brings rays of light into focus on the retina.

Macula: is a small area of the retina located near the optic nerve at the back of the eye. It is responsible for our central, most acute vision.

Optic Nerve: the important nerve that carries messages from the retina to the brain.

Pupil: the circular opening at the center of the iris that controls the amount of light into the eye.

Retina: the inner layer of the eye containing light-sensitive cells that connect with the brain through the optic nerve. It also contains retinal blood vessels which feed the retina and which can be affected by diabetes.

Sclera: the white part of the eye that is a tough coating which, along with the cornea, forms the external protective coat of the eye.

Vitreous Body: a colorless mass of soft, gelatin-like material that fills the eyeball behind the lens.

 

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