HOW THE EYE WORKS
The five senses include sight, sound, taste, hearing and touch. Sight, like the other senses is closely related to other parts of our anatomy. The eye is connected to the brain and dependent upon the brain to interpret what we see.
How we see depends upon the transfer of light. Light passes through the front of the eye (cornea) to the lens. The cornea and the lens help to focus the light rays onto the back of the eye (retina). The cells in the retina absorb and convert the light to electrochemical impulses, which are transferred along the optic nerve and then to the brain.
The eye works much like a camera. The shutter of a camera can close or open depending upon the amount of light needed to expose the film in the back of the camera. The iris and the pupil, like the camera shutter, control how much light to let into the back of the eye. When it is very dark, our pupils are very large, letting in more light. The lens of a camera is able to focus on objects far away and up close with the help of mirrors and other mechanical devices. The lens of the eye helps us to focus but sometimes needs some additional help in order to focus clearly. Glasses, contact lenses, and artificial lenses all help us to see more clearly.
ANATOMY OF THE EYE
Choroid – Layer containing blood vessels that lines the back of the eye and is located between the retina (the inner light-sensitive layer) and the sclera (the outer white eye wall).
Ciliary Body – Structure containing muscle and is located behind the iris, which focuses the lens.
Cornea – The clear front window of the eye which transmits and focuses (i.e., sharpness or clarity) light into the eye. Corrective laser surgery reshapes the cornea, changing the focus.
Fovea – The center of the macula, which provides the sharp vision.
Iris – The colored part of the eye which helps regulate the amount of light entering the eye. When there is bright light, the iris closes the pupil to let in less light. And when there is low light, the iris opens up the pupil to let in more light.
Lens – Focuses light rays onto the retina. Our lens deteriorates as we age, resulting in the need for reading glasses. The lens is transparent at birth, but become cloudy as we age. In cataract surgery, intraocular lenses are used to replace our natural lens when it becomes clouded by cataracts.
Macula – The area in the retina that contains special light-sensitive cells. In the macula these light-sensitive cells allow us to see fine details clearly in the center of our visual field. The deterioration of the macula is a common condition as we age (age related macular degeneration or ARMD).
Optic Nerve – A bundle of more than a million nerve fibers carrying visual messages from the retina to the brain. (In order to see, we must have light and our eyes must be connected to the brain.) Your brain actually controls what you see, since it combines images. The retina sees images upside down but the brain turns images right side up. This reversal of the images that we see is much like a mirror in a camera. Glaucoma is one of the most common eye conditions related to optic nerve damage.
Pupil – The dark center opening in the middle of the iris. The pupil changes size to adjust for the amount of light available (smaller for bright light and larger for low light). This opening and closing of light into the eye is much like the aperture in most 35 mm cameras which lets in more or less light depending upon the conditions.
Retina – The nerve layer lining the back of the eye. The retina senses light and creates electrical impulses that are sent through the optic nerve to the brain.
Sclera – The white outer coat of the eye, surrounding the iris.
Vitreous Humor – The, clear, gelatinous substance filling the central cavity of the eye.