The amazing inner working of your eye Click image to enlarge Your eyes are working from the moment you wake up to the moment you go to sleep. Your eyes take in an enormous amount of information about the world around you – shapes, colors, movements, and more. They then send the information to your brain, where it's processed, so the brain knows what's going on outside of your body. The eye is a very complex organ that is approximately 1 inch (2.54 cm) wide, 1 inch deep and 0.9 inches (2.3 cm) tall. Following are explanations for some of the various parts of the eye: Cornea: The transparent front "window" of the eye that covers the iris and pupil, and provides most of the eye's optical power. Pupil: The variable-sized black circular opening in the center of the iris, the pupil regulates the amount of light that enters the eye. Iris: The colored portion of your eye that surrounds the pupil. This expands and contracts, allowing light to enter through the pupil. Lens: The transparent, biconvex lens of the eye helps bring rays of light to focus on the retina. Vitreous: The clear, jelly-like substance that fills the rear cavity of your eyeball. The vitreous takes up two-thirds of your eyeball. Aqueous humor: This is a thin, watery substance that fills the front part of the eye and gives your eye its form. It fills the area between the lens and the cornea. It is continuously produced by the ciliary body, and gives nourishment to the lens and the cornea. Macula: The small, specialized central area of the retina, the macula is responsible for acute central vision. Retina: The lining of the rear two-thirds of the eye, the retina converts images from the eye's optical system into electrical impulses sent along the optic nerve to the brain. Optic nerve: A bundle of nerve fibers that carry impulses for sight from the retina to the brain.