Post on 12-Jan-2016
HEALTHY CHOICES: Your Sense of Sight
Ms. Mai
Lawndale High School
Your Sense of Sight
Your eyes are delicate organs
The bones on your face guard them from injury
Your eyelashes and eyelids screen our dirt
Tears keep the eyes’ surface moist and clean
Your eyes has many internal structures that function together to produce vision
How Your Eyes See
Vision begins with the light rays striking the cornea (clear covering at the front of your eye)
The cornea bends the light rays so they pass through the pupil (round opening in the center of your eye)
Controlling the Amount of Light
The iris is the colored circle surrounding the pupil that controls the size of the pupilThe iris also controls the amount of light entering the inner eye
In dim light, the iris relaxes to make your pupils larger and allow in more light
In bright light, the muscles contract to make your pupil small and block out some light
Focusing the Light Rays
Light rays pass through the pupil and into the curved lens behind itThe lens bends the light rays so they come together at a point inside your eye
In order to focus correctly, the lens must change shape as you look at objects closer and farther away
The muscles attached to the lens relaxes or contracts to change its shape
Sensing Light and Color
The retina is a light-sensitive tissue that lines the inner eye
The retina contains receptors called rods and cones that are sensitive to light
The rods can differentiate black from white, while the cones can distinguish color
Creating Nerve Impulses
Light striking the retina causes chemical changes in the rods and cones
These changes produce nerve impulses that are passed to the optic nerve that connects the eye with the brain
The optic nerve transmits the impulses to your brain
Interpreting Impulses
You do not see anything until the impulses are interpreted by your brain
The brain decodes the impulses and processes them to get meaningful informationYour brain coordinates and interprets information from both eyes at the same time
Because each eye views an object from a different angle, the two overlapping images enables us to judge depth of an image
Common Eye Problems
The two most common vision problems are nearsightedness and farsightedness
Nearsightedness – a person sees closer objects clearly, but objects at a distance looked blurred
Farsightedness – a person sees distant objects clearly, but objects that are closer looked blurred
Which is which?
Common Eye Problems
Both nearsightedness and farsightedness are cause by the eyeball being shaped incorrectly, so light rays do not focus on the retina correctly
Both can be corrected by wearing a curved lens in front of the eye to bend the light rays entering the eye so that they focus correctly
Astigmatism
Astigmatism is a condition that causes blurred vision at all distances because the cornea or the lens is irregularly shaped
Color Blindness
Color blindness is a hereditary disorder in which the person cannot distinguish between certain colors (red and green especially)
Eye Diseases
A sty is an infection at the base of an eyelash
Pinkeye is an inflammation of the eyelid’s inner lining caused by infection from bacteria or a virus
Detached Retina
A detached retina occurs when the retina tears away from the inner eyeball producing a blind area at the tear
Glaucoma
Glaucoma is caused by increased pressure of the fluids inside the eye, which then damages the retina leading to blindness
Eye DiseasesA cataract is a condition in which the lens becomes cloudy and blocks light from entering the eye
If the cornea becomes too scarred from disease or injury, blindness will occur
A corneal transplant can restore a person’s vision by taking a healthy cornea from a donor who has recently died and replacing the damaged cornea
Caring for your Eyes
Good eye care includes protecting your eyes against irritations, infections, and injury
Make sure your hands are clean before touching around your eyes
Always wear safety goggles when handling chemicals, working with power tools, playing certain sports, and in other situations that may cause injury to your eye
Vision Checkups
If you notice any change in your vision, you should have a vision checkup right away (usually every 2 to 4 years otherwise)
Normal vision is said to be 20/20, which means that you can read at 20 feet what people with normal vision can read at 20 feet
20/40 vision means that you can read at 20 feet what people with normal vision can read at 40 feet
Vision Checkups
After checking your vision, the doctor will look into each eye to check the clarity of the cornea, lens, fluids and the conditions of the retina
The doctor may also measure the fluid pressure inside each eye to check for early signs of glaucoma
Corrective Lenses
If you have a vision problem, the doctor will give you a prescription for corrective lenses
People will get eyeglasses or contact lenses depending upon the activities they participate
Wearing sunglasses that protect against UV rays can help protect your eyes from damage
Working with VDT
Working with a video display terminal (vdt) like a computer can cause eyestrain
The symptoms of eyestrain include blurred vision, headache, and a burning feeling in your eye
To prevent eyestrain, take frequent breaks and focus your eyes on distant objects