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Parts of eye and their function

Eye anatomy - AN0003

Sclera

The white part of the eyeball is called the sclera (SKLAIR-uh). The sclera is made of a tough material and has the important job of covering most of the eyeball. Think of the sclera as your eyeball’s outer coat. Look very closely at the white of the eye, and you’ll see lines that look like tiny pink threads. These are blood vessels, the tiny tubes that deliver blood, to the sclera.

Cornea

The cornea (KOR-nee-uh), a transparent dome, sits in front of the colored part of the eye. The cornea helps the eye focus as light makes its way through. It is a very important part of the eye, but you can hardly see it because it’s made of clear tissue. Like clear glass, the cornea gives your eye a clear window to view the world through.

Iris

Behind the cornea are the iris, the pupil, and the anterior chamber. The iris (EYE-riss) is the colorful part of the eye. When we say a person has blue eyes, we really mean the person has blue irises! The iris has muscles attached to it that change its shape. This allows the iris to control how much light goes through the pupil(PYOO-pul).

Pupilcornea

The pupil is the black circle in the center of the iris, which is really an opening in the iris, and it lets light enter the eye. To see how this works, use a small flashlight to see how your eyes or a friend’s eyes respond to changes in brightness. The pupils will get smaller when the light shines near them and they’ll open wider when the light is gone.

Anterior chamber

The anterior (AN-teer-ee-ur) chamber is the space between the cornea and the iris. This space is filled with a special transparent fluid that nourishes the eye and keeps it healthy.

Lens-Light and Action

These next parts are really cool, but you can’t see them with just your own eyes! Doctors use special microscopes to look at these inner parts of the eye, such as the lens.eye_xsection_01

After light enters the pupil, it hits the lens. The lens sits behind the iris and is clear and colorless. The lens’ job is to focus light rays on the back of the eyeball — a part called the retina (RET-i-nuh).

The lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a sharp real image of the object of interest to be formed on the retina.

The lens works much like the lens of a movie projector at the movies. Next time you sit in the dark theater, look behind you at the stream of light coming from the projection booth. This light goes through a powerful lens, which is focusing the images onto the screen, so you can see the movie clearly. In the eye’s case, however, the film screen is your retina.

Retina

Retina is the third and inner coat of the eye which is a light-sensitive layer of tissue. The optics of the eye create an image of the visual world on the retina (through the cornea and lens), which serves much the same function as the film in a camera. Your retina is in the very back of the eye. It holds millions of cells that are sensitive to light. The retina takes the light the eye receives and changes it into nerve signals so the brain can understand what the eye is seeing.

Ciliary muscle

The lens is suspended in the eye by a bunch of fibers. These fibers are attached to a muscle called the ciliary (SIL-ee-air-ee) muscle. Ciliary muscle is a circular muscle that relaxes or tightens the zonules to enable the lens to change shape for focusing. The zonules are fibers that hold the lens suspended in position and enable it to change shape during accommodation.

The ciliary muscle has the amazing job of changing the shape of the lens. That’s right — the lens actually changes shape right inside your eye! Try looking away from your computer and focusing on something way across the room. Even though you didn’t feel a thing, the shape of your lenses changed. When you look at things up close, the lens becomes thicker to focus the correct image onto the retina. When you look at things far away, the lens becomes thinner.

Vitreous body

The biggest part of the eye sits behind the lens and is called the vitreous (VIH-tree-us) body. The vitreous body forms two thirds of the eye’s volume and gives the eye its shape. It’s filled with a clear, jelly-like material called the vitreous humor. In eye, after light passes through the lens, it shines straight through the vitreous humor to the back of the eye.

Rods and Cones Process Lightrodscones_01

The retina uses special cells called rods and cones to process light. Just how many rods and cones does your retina have? How about 120 million rods and 7 million cones — in each eye!

Rods see in black, white, and shades of gray and tell us the form or shape that something has. Rods can’t tell the difference between colors, but they are super-sensitive, allowing us to see when it’s very dark.

Cones sense color and they need more light than rods to work well. Cones are most helpful in normal or bright light. The retina has three types of cones. Each cone type is sensitive to one of three different colors — red, green, or blue — to help you see different ranges of color. Together, these cones can sense combinations of light waves that enable our eyes to see millions of colors.cones-and-rods-wavelength

Rods and cones process the light to give you the total picture. You’re able to see that your friend has brown skin and is wearing a blue hat while he tosses an orange basketball.

Optic nerve

Think of the optic nerve as the great messenger in the back of your eye. The rods and cones of the retina change the colors and shapes you see into millions of nerve messages. Then, the optic nerve carries those messages from the eye to the brain!

The optic nerve is located in the back of the eye. It is also called the second cranial nerve or cranial nerve II. It is the second of several pairs of cranial nerves. The job of the optic nerve is to transfer visual information from the retina to the vision centers of the brain via electrical impulses.

The optic nerve is made of ganglionic cells or nerve cells. It consists of over one million nerve fibers. Our blind spot is caused by the absence of specialized photosensitive (light-sensitive) cells, or photoreceptors, in the part of the retina where the optic nerve exits the eye.

The optic nerve serves information through electrical impulses to the brain. When you see an image, your brain with the help of that information translate what you are seeing, a “cat,” “tree” or “house” or whatever the case may be.

 Lacrimal glands

Have No Fear, You Have Tears

The eye has its own special bathing system — tears! Above the outer corner of each eye are the lacrimal (LAK-ruh-mul) glands, which make tears. Lacrimal gland is a small almond-shaped structure that produces tears and is located just above the upper, outer corner of the eye. Every time you blink your eye, a tiny bit of tear fluid comes out of your upper eyelid. It helps wash away germs, dust, or other particles that don’t belong in your eye.lacrimal

Tears also keep your eye from drying out. Then the fluid drains out of your eye by going into the lacrimal duct (this is also called the tear duct). You can see the opening of your tear duct if you very gently pull down the inside corner of your eye. When you see a tiny little hole, you’ve found the tear duct.

Your eyes sometimes make more tear fluid than normal to protect themselves. This may have happened to you if you’ve been poked in the eye, if you’ve been in a dusty or smoking area, or if you’ve been near someone who’s cutting onions.

And how about the last time you felt sad, scared, or upset? Your eyes got a message from your brain to make you cry, and the lacrimal glands made many, many tears.

 

How to keep your Eyes Healthy

Get Regular Eye Exams 

Foods to improve Your Eye Health

Have a Comprehensive Dilated Eye Exam

Eye safety tips from computer screen

Common Vision Problems

 Age-related Eye Diseases

 

 

 

 

Related Topics

How to choose sunglasses

Kinds of Contact Lenses

Some interesting Eye Facts


 

Reference

http://www.webmd.com/eye-health/features/tips-for-healthy-eyes#3

https://nei.nih.gov/healthyeyes/eyehealthtips

http://kidshealth.org/en/kids/eyes.html#

http://www.allaboutvision.com/nutrition/foods.htm

http://www.bausch.com/vision-and-age/20s-and-30s-eyes/healthy-eyes

http://www.healthline.com/human-body-maps/optic-nerve

https://en.wikipedia.org/wiki/Human_eye

http://www.medicinenet.com/script/main/art.asp?articlekey=10609

http://www.aao.org/eye-health/tips-prevention/top-sunglasses-tips

http://www.aoa.org/patients-and-public/caring-for-your-vision/contact-lenses/advantages-and-disadvantages-of-various-types-of-contact-lenses?sso=y

http://www.everydayhealth.com/vision-center/lenses-and-beyond/contact-lens-options.aspx

https://www.reference.com/science/big-human-eye-59a54b764d3ea21e#

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