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