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 pupil The 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 it The 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 information Your 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 Diseases A 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