How The Eye Works
The eye works basically like a camera. Light comes through a small hole, the pupil, which is like the lens opening on a camera. The image is then focused onto the retina by the eye's lens, just as a camera lens registers an image onto film. The coloured ring of the eye, the iris, controls the amount of light allowed into the eye. It automatically opens (dilates) and closes (contracts) the pupil when the light around you changes.
The human eye is, of course, more complex than a camera. The outside of the eye is covered by a tough white sheath called the sclera. The front part of the eye is the cornea, a clear covering that allows light to enter. Muscles inside the eye automatically change the shape of the lens to focus light on the retina. This delicate sheet of light-sensitive nerve tissue collects and transmits images to the brain via the optic nerve.