Anatomy Of The Eye
The eye has been called the most complex organ in the body. It's amazing that something so small can have so many working parts. But when you consider how difficult the task of providing vision really is, perhaps it's no wonder after all.
The eye is like a camera. It lets light in through the cornea, which is like a camera's opening. The amount of light allowed in is controlled by the pupil, which opens and closes a bit like a shutter. The light focuses on the retina, which sends the image to the brain, acting as film would in order to record the light (the photo itself).
Other eye structures support the main activity of sight. Some carry fluids - tears and blood - to lubricate or nourish the eye. Others are muscles that allow the eye to move. Some protect the eye from injury - lids and the epithelium of the cornea. And some are messengers, sending sensory information to the brain - pain-sensing nerves in the cornea and the optic nerve behind the retina.
|Step 1: Light rays, or photons, enter the eye's outer, transparent layer of tissue (the cornea), then pass through the dark, circular opening (the pupil) in the center of the colored iris. The pupil regulates the amount of light that enters the eye.|
|Step 2: The light rays strike the inner (or crystalline) lens of the eye. This lens focuses the rays on the retina -- a layer of light-sensitive cells that line the inside back wall of the eye.|
|Step 3: The cells in the retina transform the photons into electrical impulses. These are transmitted through the optic nerve to the brain, where complex electrical-chemical interactions give us the sensation of seeing.|
The electrical and chemical communications that take place between the retina and the brain are fascinatingly complex. They are so complex, in fact, that it's difficult to know whether seeing actually takes place in the eye or in the mind.