anatomy of theeye

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Anatomy of the Eye

Prepared by:

Ahmed Bayazeed

Spervised by:

prof.mahmoud abdelmoneim 

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Sclera

The white part of theeyeball is called thesclera (say: sklair-uh). The sclera is

made of a toughmaterial and has theimportant job of covering most of theeyeball. Think of thesclera as youreyeball's outer coat.

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Cont…  Look very closely at the white of the

eye, and you'll see lines that look liketiny pink threads. These are bloodvessels, the tiny tubes that deliverblood, to the sclera.

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CORNEA

The part of the sclera in front of the coloredpart of the eye is called the cornea (say:kor-nee-uh). Unlike the rest of the sclera,which is white, the cornea is transparent,

or completely clear, which lets light travelthrough it. The cornea helps the eye focusas light makes its way through. It is a veryimportant part of the eye, but you canhardly see it because it's made of clear

tissue. Like clear glass, the cornea givesyour eye a clear window to view the worldthrough

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On cross section, the cornea

contains five distinct layers. The outside layer is Epithelial cells.  Bowman’s layer. 

Stroma.

Descemet’s membrane. 

Endothelium is the final inner layer.

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IRIS

The iris (say: eye-riss) is thecolored part of the eye calledthe iris.It controls light levelsinside the eye similar to theaperture on a camera. Theround opening in the center of the iris is called the pupil. The

iris is embedded with tinymuscles that dilate (widen)and constrict (narrow) the

pupil size.

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Cont… The iris is flat and divides the

front of the eye (anterior

chamber) from the back of theeye (posterior chamber). Itscolor comes from microscopicpigment cells called melanin.The color, texture, andpatterns of each person's irisare as unique as a

fingerprint. 

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Anterior chamber  Between the iris and

cornea is the anterior (say: an-teer-ee-ur)chamber. This

chamber is filled with aspecial transparentfluid that gives the eyeoxygen, protein, andglucose (a type of sugar in the body) tokeep it healthy.

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PUPIL

The iris is a muscle. This allows theiris to control how much light goesthrough the pupil (say: pyoo-pul).The pupil is the black circle in thecenter of the iris, and it lets lightenter the eye. The pupils will get

smaller when a light shines near themand they'll open wider when the lightis gone.

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Cont…  Its size is generally

altered only by actions of the sphincter and dilator

muscles, although it canbe changed bymedications and surgery.

An average size can beestimated at 2 mm to 4

mm. 

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  After light entersthe pupil, it hitsthe lens. The lenssits behind the irisand is clear andcolorless. The lens' job is to focus lightrays on the back of 

the eyeball - a partcalled the retina (say: reh-tin-uh).

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Retina

Your retina is in thevery back of the eye,past the vitreous body.Though it's smaller

than a dime, it holdsmillions of cells thatare sensitive to light.The retina takes thelight the eye receivesand changes it intonerve signals so thebrain can understandwhat the eye is seeing.

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Rods and Cones 

The retina uses specialcells called rods andcones to process light.Just how many rods andcones does your retinahave? How about 120million rods and 7 millioncones - in each eye!

Rods and cones are mostsensitive to yellow-greenlight.

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RODS

Rods see in black,white, and shades of gray and tell us the

form or shape thatsomething has. Rodscan't tell thedifference between

colors, but they aresuper-sensitive,allowing us to seewhen it's very dark.

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CONES

Cones sense color and they needmore light than

rods to work well.Cones are mosthelpful in normal orbright light.

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Cont…  The retina has three types of cones -

red, green, and blue - to help you seedifferent ranges of color. Together,these cones can sense combinationsof light waves that enable our eyes tosee millions of colors.

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Ciliary muscle 

The lens is suspended in the eye by a bunch of 

fibers. These fibers are attached to a musclecalled the ciliary (say: sih-lee-air-ee) muscle.The ciliary muscle has the amazing job of changing the shape of the lens.

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ciliary body  The ciliary body lies just behind

the iris iris. Attached to the ciliary bodyare tiny fiber "guy wires" called zonules.

One function of the ciliary body is theproduction of aqueous, the clear fluid thatfills the front of the eye. Italso controls accommodation by changingthe shape of the crystalline lens. When the

ciliary body contracts, the zonules relax.This allows the lens to thicken, increasingthe eye's ability to focus up close.

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Aqueous Humor 

The aqueous is the thin, watery

fluid that fills the space betweenthecornea and the iris (anteriorchamber). It is continuallyproduced by the ciliary body, thepart of the eye that lies justbehind the iris. This fluidnourishes the cornea and the lensand gives the eye it's shape.

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VITREOUS BODY 

The biggest part of the eye sits behind thelens and is called the vitreous (say: vih-tree-us) body. The vitreous body forms

two thirds of the eye's volume and givesthe eye its shape. It's filled with a clear, jelly-like material called the vitreoushumor.

In eye, after light passes through the lens,it shines straight through the vitreoushumor to the back of the eye.

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Reflected light

Reaches the retinawhere it falls onto thecones and rods.

The critical part of theimaging process is thelens.

The lens gives thedetailed information

about the size, shape,and color of an object.

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Lens 

The crystalline lens is located justbehind the iris. Its purpose is to

focus light onto the retina. Thenucleus, the innermost part of the lens, is surrounded by softermaterial called the cortex. Thelens is encased in a capsular-likebag and suspended within theeye by tiny "guy wires" calledzonules.

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Cont… In young people, the lens

changes shape to

adjust for close ordistance vision. This iscalled accommodation.With age, the lensgradually hardens,diminishing the abilityto accommodate.

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Protection Because the eye is such an

important and complex part of our body, we have manyfeatures which protect the eye.

The eyebrows are the strips of hair aboveyour eyes which prevent sweat from runninginto them.

Eyelashes help keep the eye clean bycollecting small dirt and dust particles floatingthrough the air. The eyelashes also protect theeye from the sun's and other light's glare. Theeyelids sweep dirt from the surface of the eye.The eyelid also protects the eye from injury.

Tears are sterile drops of clean water whichconstantly bathe the front of the eye, keepingit clean and moist.

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Extraocular Muscles The six tiny muscles that surround the eye and control its

movements are known as the extraocular muscles(EOMs). The primary function of the four rectus musclesis to control the eye's movements from left to right and

up and down. The two oblique muscles move the eyerotate the eyes inward and outward.

All six muscles work in unison to move the eye. As onecontracts, the opposing muscle relaxes, creating smooth

movements. In addition to the muscles of one eyeworking together in a coordinated effort, the muscles of both eyes work in unison so that the eyes are alwaysaligned. 

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The six tiny muscles thatsurround the eye 

Superior rectus – moves eye up

Inferior rectus – moves eye down

Medial rectus – moves eye in (a-d-

duction)

Lateral rectus – moves eye out (a-b-duction)

Inferior oblique – moves eye up when

it is in an adducted position; alsoextorts the eye.

Superior oblique – moves eye down when it is adducted; also intorts theeye.

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Isolating ExtraocularMuscles 

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To the Brain

Think of the optic nerve as the greatmessenger in the back of your eye.The rods and cones of the retina

change the colors and shapes you seeinto millions of nerve messages.Then, the optic nerve carries thosemessages from the eye to the brain!

The optic nerve serves as a high-speed telephone line connecting theeye to the brain.

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Eye Fun Facts  Most people blink every 2-10 seconds.Each time you blink, you

shut your eyes for 0.3 seconds, which means your eyes areclosed at least 30 minutes a day just from blinking.

If you only had one eye, everything would appear two-dimensional. (This does not work just by closing one eye.) 

Owls can see a mouse moving over 150 feet away with light nobrighter than a candle.

The reason cat's and dog's eyes glow at night is because of silver mirrors in the back of their eyes called the tapetum. Thismakes it easier for them to see at night.

An ostrich has eyes that are two inches across. Each eye weighsmore than their brain.

A chameleon's eyes can look in opposite directions at the sametime.

A newborn baby sees the world upside down because it takessome time for the baby's brain to learn to turn the picture right-side up.

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Reference 

http://www.stlukeseye.com/anatomy / 

http://www.kidshealth.org/kid/body/eye_noSW.html 

http://www.allaboutvision.com/resources/anatomy.htm 

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