Medical Health Encyclopedia

The Light-Processing Parts. To understand sight, one begins with light and its passage through the eye's sensitive camera-like structures:

• Light first passes through the cornea, a clear tissue at the front of the eye.
• Behind the cornea, the iris (the colored tissues of the eye) opens and closes like a camera shutter to regulate the passage of light.
• The lens, located behind the iris, focuses the light, which then hits the retina.
• The retina is an electric fragile membrane of nerve cells called photoreceptors that receive light and translate it into signals.
• A layer of cells, called the retinal ganglia, receive signals from the retina. These nerve cells are the front ends of the optic nerve cable, which, in turn, receive the signals.
• The optic nerve is actually a cable of about 1.2 million nerve fibers called axons. It carries the signals to the brain, which interprets them as images.
• They exit the eye through the optic disc, located in the back of the eye.

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The Supportive Chambers. To help support and protect these sensitive structures, the eye contains two fluid-filled chambers:

• The posterior (rear) chamber is the large area behind the iris.
• Fluid passes from the posterior into the anterior (forward) chamber located in the bulging area between the iris and the front of the eye.