1. Health 7
Chapter 14 Lesson 3

2. Healthy Eyes and Ears THE STRUCTURE OF THE EYE
Your eyes enable you to distinguish shapes, colors, movement and light.
The main parts of the eye are detailed below.
The cornea is a clear protective structure that lets in light.
The iris is the colored part of the eye. It controls the size of the pupil.

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3. The aqueous humor is the watery fluid between the cornea and the lens. It helps maintain pressure in the eye.
4. The lens is a clear, flexible structure that focuses light on the retina.

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5. The retina is a thin layer of nerve cells that absorb light. It covers the interior back of the eye.
6. The optic nerve is a cord of nerve fibers that carry messages from the retina to the brain.

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6. Healthy Eyes and Ears C. The human eye is similar to a camera
D. Light passes through the cornea, aqueous humor, pupil and lens to the retina.
E. The nerve endings distinguish objects in shades of black, white, and grey. Other nerve endings called cones distinguish red, blue and green.

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F. A person who is missing one or more kinds of cones in unable to distinguish certain colors, an inherited condition called color blindness.

9. Healthy Eyes and Ears II. PROTECTING YOUR EYES
Protecting your eyes from injury, dust and overexposure to sunlight is a positive health habit. Here are some guidelines:
wear protective eyewear when participating in an activity that could injure the eyes
read, watch television and use the computer in a well-lit room

10. Healthy Eyes and Ears c. take breaks from using your eyes
d. avoid touching your eyeballs when applying makeup

11. Healthy Eyes and Ears III. GETTING YOUR EYES CHECKED
Two kinds of professionals provide eye checkups:
An optometrist is a professional who checks your vision and prescribers corrective lenses.
An ophthalmologist is a medical doctor who specializes in the medical and surgical treatment of the eyes, and who prescribers corrective lenses.

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B. If you wear glasses or contact lenses, have your eyes checked once a year. If you don’t wear glasses or contact lenses, every two years is sufficient.
C. Common visions problems are:
Farsightedness - distant objects and clear, but nearby objects appear blurred.

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2. Nearsightedness - A person can see nearby objects clearly, but distant objects appear blurred.
3. Astigmatism - Images are distorted or blurred because of an irregularly shaped lens or cornea.

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E. Some vision problems can be corrected with surgery.
Laser surgery to reshape the cornea
Surgery to remove cataracts
Transplants - lens, cornea

15. Healthy Eyes and Ears F. The examination of the eye consists of:
Inspection of the lens, cornea, pupil for clearness
Check the eye for glaucoma - a disease of vessels draining liquid in the eye. Early detection can prevent blindness

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3. Check for cataracts - clouding of the lens, corrected by surgery
4. Check vision - checks the size of letters you can see from 20 feet away. 20/20 is considered good vision.

17. Healthy Eyes and Ears IV. THE STRUCTURE OF THE EAR
You might think of your ears as external to your head, but in fact they go deep into your skull.
the ear has three main parts:
The outer ear - the fleshy curved part attached to your head
Why do your think your outer ear is cup shaped

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2. The middle ear
3. The inner ear

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20. Healthy Eyes and Ears V. HOW YOUR EARS WORK
Hearing involves a fairly complicated chain of events.
First, the outer ear guides sound waves through the auditory canal to the middle ear, where they cause the eardrum to vibrate.
This vibration moves three tiny bones in the middle ear; the hammer, anvil and stirrup.

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4. The bones then transmit the vibration to the oval window in the inner ear.
5. The oval window causes fluid in the cochlea to move.
6. The movement of this fluid sets tiny hairs inside the cochlea in motion. (15,000)

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7. The hair cells produce electrical messages that travel through the auditory nerve to the brain, which interprets the messages enabling you to identify the sound.

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8. The Eustachian tube is the part of the ear that allows air to pass from the nose to the middle ear so the air pressure is equal on both sides of the eardrum.
9. The Semicircular canals in the inner ear control your balance.

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10. Two common balance problems are dizziness and motion sickness.
E. Cochlear implants - can help hearing impaired to hear
The device is a tiny microphone and sound processor

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b. It picks up sound waves and converts them to electronic signals
c. It passes the signals to a receiver planted in the skin behind the ear.

26. Healthy Eyes and Ears VI. PROTECTING YOUR EARS
Over time, loud noises can cause permanent hearing loss.
A decibel is a measure of the loudness of a sound.

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C. Tinnitus is a condition in which a constant ringing sound is heard in the ear.
D. here are some ways to protect your ears.
Cover your ears with earmuffs, a hat and a scarf in cold weather
Keep foreign objects and sharp objects and cotton swabs out of your ears.

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3. Wear hearing protection, such as ear plugs, when you are exposed to loud noises at a concert, shooting,m or indoor sporting event.

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