In many ways, our eyes resemble an extraordinarily sensitive camera. Much like a camera lens, the lens of the eye can change shape to focus on near or distant objects. The lens projects images on the retina, a layer of light sensitive cells on the back of the eye, functions much like the film in a camera.
The eye is connected to the brain by the optic nerve, a bundle of over one million nerve fibers. The cornea (the clear portion of the front of the eye) bends light rays through the pupil to the lens. The pupil is the black opening in the iris. The iris, the colored ring of tissue, regulates the amount of light entering the eye by adjusting the size of the pupil. The eye also has fluids that bathe the various parts of the eye and help to maintain the correct pressure within the eye. The anterior chamber, in the front of the eye, is filled with aqueous humor, a watery fluid. The back portion of the eye is filled with a clear jelly like substance, called the vitreous humor.
The eye can be divided into three layers (or tissues). The white outer coat of the eye, the sclera, is similar to the shell of an egg. Along with the cornea, the sclera protects the eye from trauma and maintains the delicate structure of the internal eye tissues. The middle tissue layer, the choroids, is the blood supply to the eye wall and outer retinal structures. This tissue is responsible for transporting nutrients and oxygen to the outer sclera and inner retinal tissue.
The innermost layer of the eye is the retina, a thin translucent tissue composed of ten microscopic layers. The retina is responsible for translating light images into electrical impulses that can be recognized and processed by the brain. The macula is the area of the retina that is responsible for central vision. The center of the macula is called the fovea, and it is responsible for very sharp vision. The retina receives images of light and transmits them to the brain via the optic nerve. The brain interprets these messages as sight.
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