The eye can be considered as a living optical device. It is approximately spherical in shape, with its outer layers, such as the outermost, white part of the eye and one of its inner layers keeping the eye essentially light tight except on the eye's optic axis. The optical components consist of a first lens that accounts for most of the optical power of the eye and accomplishes most of the focusing of light from the outside world; then an aperture in a diaphragm (the iris—the coloured part of the eye) that controls the amount of light entering the interior of the eye; then another lens that accomplishes the remaining focusing of light into images; and finally a light-sensitive part of the eye (the retina), where the images fall and are processed. The retina makes a connection to the brain via the optic nerve.