September 21, 2004

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The Eye
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aqueous humor - a clear fluid that helps the cornea keep its rounded shape
astigmatism - a condition of the eye in which the cornea curves severely, like a football, instead of having a normal rounded shape. Astigmatism is inherited, and can occur in combination with nearsightedness or farsightedness.
binocular vision - vision as a result of both eyes working as a team; when both eyes work together smoothly, accurately, equally and simultaneously.
blind spot - the area of the retina where the optic nerve and blood vessels enter the eye. It is called "blind" because there are no rods and cones to make vision possible.
blood vessels - deliver blood to the eye through the optic nerve
ciliary body - muscles that control the shape of the lens for near and far vision

- the part of the eye that lies between the retina and the sclera coat and is made
of layers of blood vessels that nourish the eye

color blindness - not being able to tell the difference between two colors, often red and green.. If all hues are perceived as variations of gray, then it it called total color blindness. Partial color blindness consists of the inability to see reds or greens or to differentiate between the reds and the greens. Occasionally, the color blindness may involve the blues or the yellows.
color vision - the ability to see different wavelengths of light  
compound eye - an eye made up of separate units, each with its own lens and optic nerve fiber. Bees and shrimp have compound eyes.

- one of two types of photoreceptor cells in the retina. Cones allow us to see color, and work best in bright light.

cornea - the tough transparent dome that covers the front of the eye. This clear "window" helps to focus light rays to the back of the eye
eye - the sense organ that detects light  
eyeball - is spherical that is about 1 inch across. It is also called "globe" and it contains many things that help us with our vision.
eyebrow - the hair on the skin over the eye, that helps to keep particles like dust out of the eye.
eyecup - clusters of light-sensitive cells that form cup-shaped depressions on an animal's body. Seastars have eyecups.  
eyelash - the hair directly above or below the eye, that helps to protect the eye  
eyelid - the fold of skin that covers the eye and protects it  
eyespot - light sensitive cells cells distributed all over an animal's body. Earthworms have eyespots.  
farsighted - occurs when the eye is shorter than normal and has too little focusing power, This is also called "hyperopia".  
fovea - dimple in the retina where cones are concentrated and vision is most acute.  
iris - specialized muscles that gives the eye its color. It adjusts the size of the pupil, to control the amount of light that enters the eye.  

- the clear flexible part of the eye that is located behind the iris and in front of the vitreous humor. The lens focuses light rays on the back of the eye and allows us to see both near and far.

macula - sensitive part of the retina responsible for detailed vision. The fovea is the very center of the macula.  
muscles - six muscles hold the eye in place, and allow it to move in many directions  
nearsighted - occurs when the eye is longer than normal and has too much focusing power. 25%% of adults in the world are nearsighted, or myopic.  
optic nerve - the bundle of nerve fibers in the back of the eye that carries visual information from the retina to the brain  
opthalmologist - is similar to an optometrist who can examine, diagnose, and make prescriptions , but an ophthalmologist also performs surgery to fix eye problems  
optician - the professional who examines eyesight and makes glasses and contact lenses
optometrist - a doctor who examines eyes, diagnoses problems, and writes prescriptions for glasses and eye medicines
orbital cavity - the bony socket in the skull which is lined with fatty tissue to cushion the eye
pupil - the black, circular opening in the center of the iris that opens and closes in order to regulate the amount of light entering the eye
retina - layer of tissue lining the inside of the eye. It contains millions of specialized light-sensitive cells which convert light into images .The retina is connected to the brain by the optic nerve.  
rods - one of two types of photoreceptor cells in the retina. Rods allow us to see black and white, and work best in dim light.
simple eye - the type of eye that can detect light and dark and sometimes motion. There are two types: eyespots and eyecups.
sclera - the thick, tough, white outer protective coating that covers the outside of the eye.  
sunglasses - eye glasses with dark lenses to keep out harmful ultraviolet rays and to reduce the amount of sunlight entering the eyes.
tapetum lucidum - the colorful, shiny material located behind the retina that is found in animals that have good night vision. It reflects light back through the retina.  
UV Radiation -ultraviolet rays of energy given off by the sun that can cause sunburns and harm your eyes  
vitreous humor - is a thick, clear fluid in the central area of the eye, that provides a cushion for the eye and gives it its shape
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