The human eye is remarkable. It accommodates to changing lighting conditions and focuses light rays originating from various distances from the eye. When all of the components of the eye function properly, light is converted to impulses and conveyed to the brain where an image is perceived.
Light rays enter the eye through a transparent layer of tissue known as the cornea.
As the eye's main focusing element, the cornea takes widely diverging rays of light and bends them through the pupil , the dark, round opening in the center of the colored iris. The lens of the eye is located immediately behind the pupil. The purpose of the lens is to make the delicate adjustments in the path of the light rays in order to bring the light into focus upon the retina , the membrane containing photoreceptor nerve cells that lines the inside back wall of the eye. The photoreceptor nerve cells of the retina change the light rays into electrical impulses and send them through the optic nerve to the brain where an image is perceived. The individual components of the eye work in a manner similar to a camera.