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The Outer Layer
The outer layer of the eye contains the sclera (the white of the eye) and the cornea (the clear covering over the front of the eye). The cornea is like a window into the eye. It lies in front of the iris (the colored part of the eye). The iris acts like the shutter of a camera, regulating the amount of light that enters the eye by enlarging or reducing the size of the pupil (the black opening in the center of the eye). Immediately behind the iris is the crystalline lens (helps you focus on things close up or far away). Between the lens and the cornea is a clear liquid called aqueous which is constantly produced and then drained from the eye through the trabecular meshwork (drains located at the base of the iris). Intraocular pressure (the eye's internal fluid pressure) is measured by how easily fluid drains from the eye. Between the crystalline lens and the retina (see innermost layer below) is a jellylike substance called the vitreous.
The Middle Layer
The middle layer of the eye is called the uvea. It contains vessels that carry blood through the eye to nourish it.
The Innermost Layer
The innermost layer of the eye is the retina (similar to film in a camera). It receives light from an image we are looking at and converts that light into electrical impulses which are sent through the fibers of the optic nerve to the brain.
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