Eye & Vision
How do our eyes work?
As light enters the eye it first passes through the cornea (the clear 'window' to the eye). Because the cornea is curved, the light rays bend. Light then passes through the pupil to the lens. The iris (the colored portion of the eye) controls the amount of light that enters the eye with muscles that cause the pupil to contract if there is too much light or to dilate if there is too little light. When light hits the curved surface of the lens it is refracted, or bent even more, so that it focuses properly on the retina. The retina then turns the light into electrical energy, which passes through the optic nerve to the brain stem, and into the occipital lobe where it is converted into an image. To summarize, the:
Cornea - is a transparent, outer 'window' and primary focusing element of the eye. The outer layer of the cornea is known as epithelium. Its main job is to protect the eye. The epithelium is made up of transparent cells that have the ability to regenerate quickly. The inner layers of the cornea are also made up of transparent tissue, which allows light to pass.
Pupil - is a dark opening in the center of the colored iris that controls how much light enters the eye. The colored iris functions like the iris of a camera, opening and closing, to control the amount of light entering through the pupil.
Lens - is the part of the eye immediately behind the iris that performs delicate focusing of light rays upon the retina. In persons under 40, the lens is soft and pliable, allowing for fine focusing from a wide variety of distances. For individuals over 40, the lens begins to become less pliable, making focusing upon objects near to the eye more difficult. This is known as presbyopia.
Retina - is a membrane lining the back of the eye that contains photoreceptor cells. These photoreceptor nerve cells react to the presence and intensity of light by sending an impulse to the brain via the optic nerve. In the brain, the multitude of nerve impulses received from the photoreceptor cells in the retina are assimilated into an image.