All About Eyes
Sight, more than any of our senses, helps us navigate the world around us. In a single glance, lasting a fraction of a second, our eyes work with our brains to tell us the size, shape, color, and texture of an object. They let us know how close it is, whether it's standing still or coming toward us, and how quickly it's moving.
The eyes are small compared with most organs, but their structure is incredibly complex. They work together to perceive depth, enabling us to judge distance and the size of objects to help us move around them. They also work with the brain, muscles, and nerves to produce complicated visual images and messages. And they constantly adapt to the changing environment — for example, adjusting so that we can easily move around in a nearly dark room or bright sunlight.
To understand how the eyes work, it's important to know about their structure and about conditions and diseases that can interfere with vision.
How Eyes Work
Only part of the eye is visible in a person's face. The whole eye — the eyeball — is about the size and shape of a ping-pong ball.
All parts of the eye are extremely delicate, so our bodies protect them in several ways. The eyeball sits in the eye socket (also called the orbit) in the skull, where it is surrounded by bone. The visible part of the eye is protected by the eyelids and the eyelashes, which keep dirt, dust, and even harmful bright light out of the eye.
Eyes are also protected by tears, which moisten them and clean out dirt, dust, and other irritants that get past the defenses of the eyelashes and eyelids. Tears also help protect against infection.
With each blink, our eyelids spread a layer of mucus, oil, and tears over the cornea, which covers the eye. The lacrimal glands in the upper outer corner of each eye socket produce tears, which, after moistening the eyes, flow into canals in the eyelids. These canals drain into the lacrimal sac, a pouch in the lower inner corner of each eye socket. Tears then exit through a passage that leads to the nose.
To see, the eye has to move. Six extraocular muscles surround the eyeball and act like the strings on a puppet, moving the eye in different directions. The muscles of each eye normally move together at the same time, allowing the two eyes to remain aligned.
Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.
© 1995-2009 The Nemours Foundation. All rights reserved.
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