The Senses

Windows on the WorldThe eyes are the most sensitive and delicate organs

we possess.

which is probably why we rely on our eyesight more than any other sense.

Our eyes are the window through which we view the world. They are responsible for four fifths of all the information our brain receives -

Pupil

Iris

Built-in Protection!

• Bony sockets: your eyes are located in bony sockets to protect them from getting hit.

• Eyebrows: your eyebrows act as eye shades.

• Eyelashes: eyelashes protect your eyes from small airborne objects.

• Tears: tears keep your eyes moist and wash the dirt away.

• Blinking: Your blink reflex automatically closes your eyelids when anything comes flying towards your eyes.

Experiment

“Stereovision”

Aim: To find out the benefit of having two eyes rather than one.

INSTRUCTIONS1. Draw out the following table

before you start the experiment.

Eye

Number of successful attempts (Out of 10)

Try 1 Try 2 Try 3Mean

Left onlyopenRight onlyopenBoth eyesopen

INSTRUCTIONS2. Get a partner and go to opposite sides of the

lab one partner will be given a tennis ball/bean-bag

to throw to their partner.

3. One partner will try to catch the tennis ball/bean

bag with the use of only one eye or both eyes open.

4. Repeat the experiment two more times to get an average.

5. Change roles and repeat the experiment.

6. Write a conclusion.

Q. Are two eyes better than one at judging the direction of sounds.

Q. Why did you repeat the experiment several times & take an average?

CONCLUSIONS

Having two eyes helps us with co-ordination by helping us judge distances.

Why do we have two eyes instead of one?

Experiments have shown that if you carry out a physical activity using two eyes are all better than using one.

You get two different pictures, one from each eye. Your brain puts the two pictures together.

This is called having binocular vision (bi=two). With binocular vision each of our eyes sees a slightly different image than the other.

tle.westone.wa.gov.au vision-guide.com

These two separate images are sent to the brain where the two images are put together to give 3D picture.

Binocular vision allows humans to work out the length, breadth and depth of a tennis ball while it is flying across the net. We can judge distances with more accuracy.

Binocular vision investigation

INSTRUCTIONS

Test 11. Close one eye.2. Hold one pencil in each hand.3. Start with your arms behind your back.4. Hold your arms straight and try to bring

the pencils together that their points touch.5. Repeat the experiment with both eyes

open.

Second test• 1. Hold your fingers in front of

your eyes and look into the distance.

• 2. Move them towards your face until you see a “sausage” appearing.

Can You See in the Dark?

• Shut the blinds and turn off the lights.

• Look at your partners pupils.

• Now quickly turn the lights on. Watch what happens to your partner’s pupils.

The iris (the coloured part of the eye) is a muscle which controls the size of the pupil.

The pupil changes size according to the amount of light available. When it is dark the pupil opens up

wide (dilates) to let as much light as possible into the eye

so you can see more clearly.

Eye Dissection

The Internal Parts of the Eye

Part Function

Cornea

Iris

Pupil

Lens

Retina

Fovea

Blind Spot

Optic Nerve

How We SeeLight passes into your eye through your pupil and forms an upside down picture of what you are look at on your retina (the lining at the back of your eyeball).

The optic nerve sends messages to your brain about the picture.

The brain then turns the picture the right way up again.

You can’t always believe what you see…

• eChalk: optical illusions

But… Don’t Take Your Sight for Granted!

• Walk when carrying sharp objects such as scissors, pens and pencils.

• Never look directly at the sun. • Use good lighting to avoid tiring your eyes

when reading, writing or using a computer. • Wear a helmet when riding a bike• Wear your seatbelt in the car. • Wear proper eye protection when you are

doing hazardous hobbies.• Wear sunglasses that block the harmful rays

from the sun.• Point sprays away from your face. Many

contain chemicals. • Tell your parents or an adult at school if your

eyes are bothering you.

Astonishing Figures

Around the world 37 million people are blind.

About 80% (4/5) of those who are blind have curable conditions.

Childhood Blindness

Of the 37 million people worldwide who are blind, around 1½ million are children (under 16). Most of these children become blind before they reach the age of five - a time when we mostly learn through sight. 

Your task…… Research and present one of

the following:

• Myopia• Hyperopia• Cataracts• River blindness• Glaucoma

• Colour blindness

• Conjunctivitis• Braille• Guide Dogs for

the Blind

Cataracts

Cataracts are the clouding of the eye's lens - the part of the eye responsible for focusing light and producing clear, sharp images.  

Cataracts can be removed by a simple operation to remove the cloudy lens and replace it with a plastic one. Normally the patient won’t even have to wear glasses after surgery.

A cataract operation costs just £17.00!