The clear substance located inside the sclera is called the vitreous, a gel-like material that gives the eye its spherical shape. In front of the sclera is the transparent, protective cornea, which provides most of the focusing power for light entering the eye.
The cornea's outermost layer of tissue contains cells that have the ability to regenerate within three days, allowing for rapid healing of superficial injuries. From the cornea, light passes through the pupil, the dark circle centered in the iris, the blue, green, brown or hazel ring of color that helps describe a person's appearance. The eye's iris also functions like the iris of a camera, opening and closing to regulate the pupil's size, which controls how much light penetrates the eye, by becoming smaller under bright conditions, or expanding in a dim environment.
Behind the iris, the lens provides fine-tuning for focusing and reading by altering its shape. The lens directs light onto the fine nerve tissue of the retina, which lines the inside wall of the eye and acts like the film in a camera. The retina converts the light into images and then into electrical impulses that are sent along the optic nerve to the brain. Within the brain, these signals undergo processing by the visual cortex, which senses and interprets them as the shapes and colors that the eye?.