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How The Eye Works
Eyes do not actually see objects; they see the light reflected by objects. When these light rays enter the eye, they are absorbed and then converted into electrical signals by retinal nerves.
In a person with normal vision, light rays enter the eye through the cornea (also known as the window of the eye), then are focused with the help of the crystalline lens. The crystalline lens is located behind the pupil at a point directly on the retina (the light sensitive nervous tissue at the back of the eyeball). These signals are subsequently sent to the brain where they are interpreted as visual images.
Much like the way a camera works, when the eye is working you are able to see a clear picture. When the eye is not working properly, the picture is not as clear (there is a refractive error). Only about four in ten people have normal visual acuity. Refractive errors can be corrected with the help of eyeglasses or contact lenses.