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eye
(i)
the organ of vision. In the embryo it develops as a direct extension of the brain, and thus it is a delicate organ; to protect it, the bones
of the skull are shaped to form a round cavity. The conjunctival sac covers the front of the eyeball and lines the upper and
lower eyelids. Tears constantly wash the eye to remove foreign objects, and the lids and eyelashes also help protect it in
front. The eyeball has three coats: the cornea is on the front of the eyeball and continuous with the tough, white sclera; the choroid is the middle layer, containing blood vessels; and the retina is the inner layer, containing the rods and cones that are sensitive to light. Behind the cornea and in front of the lens is the circular, pigmented iris that surrounds the pupil; the iris works like the diaphragm of a camera, adjusting the size of the pupil according to different light conditions.
Cross section of the eye.
Copyright 2007. An Elsevier publication. All rights reserved.
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