Eyes - facts and questions
Conjunctivitis; eye; colour; blindness; colour; blind; animal eye; optical illusions; conjunctiva;?genes; light; reflect; mirage; germs; cats; reflections; tricks ;
Contents
In our other topics about eyes, you can find out about the parts of the eye and how they work, how to care for your eyes and all about wearing glasses. In this topic you can find the answers to some more questions about eyes.
What is conjunctivitis?
This is when the conjunctiva (say con-junk-ty-a) (the lining of the eyelids and the front part of the white of the eye) gets sore, red and watery. The eye may be sore or itchy and your eyelids might stick together with yellow pus.
It feels like there is something in your eye.
Most times it is caused by a viral or bacterial infection (germs).
It can also be caused by allergies, hay fever, chlorine from swimming in pool water, or sometimes it is part of having an illness like measles. |
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What to do
Don't rub your eye. This will make it feel worse.
Tell mum. You may need to see a doctor.
Mum may need to wash your eyes carefully, using warm water and a cotton ball. She will need to be careful to throw the cotton ball away and wash her hands well before touching her own eyes, because conjunctivitis spreads very easily. The school may want you to stay at home until the conjunctivitis has gone, to make sure that other children and teachers don't catch it from you.
Use your own towel and face washer and don't share them with others.
The doctor may give you some eye-drops or ointment to make it better.
What is colour blindness?
Some people cannot see all the colours, or may not see the difference between certain colours. This is because some of the cells on the retina are missing or do not work properly. Usually they can't see the difference between red and green.
Boys are more likely to be colour blind than girls are. (It's all in your genes - not the denim ones!)
Special pictures are used by doctors and opticians to check if you can see all the colours properly.
Have a look at the topic 'Colour blindness' for more information.
How can cats see in the dark?
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Well they can't actually see if there is no light at all. |
| In very poor light a cat's pupils dilate [they get bigger]. This means that more light gets into the eye. Remember that eyes see 'reflected' light? This means that cats can see when it is very dark. |
Owls have such big pupils that they can see really well at night, which is when they hunt for food.
Human pupils get bigger too, but we can't see as well as cats can, because cats have a "crystalline" layer in their eyes (this is explained in the next paragraph).
Why do animals' eyes shine in the dark?
Many animals have a special layer in their eyes. It is called a crystalline layer. If even a tiny amount of light gets into their eyes, it gets reflected around inside their eyes so that they can see it. It also means their eyes reflect back light, so that if a light shines on them, the reflection from their eyes can be seen in the dark.
Have you noticed that when you use a flash to take a photo, sometimes the eyes of the person in that photo look red? This is because their eyes are reflecting back the light, and since there are a lot of blood vessels on the retina, the reflection looks red.
Historical Note
A clever man, Edwin Shaw of Halifax in England, noticed this and he made special 'cats eyes' out of glass, set them into rubber, and you will find them in the middle of roads all over the world, helping drivers see where the road goes.
How do your eyes play tricks on you?
On a hot day if you look into the distance, you may see things which are not really there because heat has made the rays of light bend.
You may see 'water' lying on the road or you may see an object floating in the sky. This is called a mirage (say mi-rarj).
Look at this picture.
What can you see? Con-cave means it looks like the hand in the picture has been pressed in, con-vex means that the hand in the picture looks like it has been pressed out towards you.
Can you tell which is which?
Are you sure?
Look again. Your eyes are really playing tricks on you aren't they?
Look at the picture below
Put one finger next to the other, like it shows in the picture (about 30cms away from your eyes). Then stare at the place where they meet for one minute.
Still staring, slowly move your fingers apart. You will see a finger floating in the air, as in the second picture.
Look at these pictures.
Which line is longer? |
Which person is bigger? |
If you measure the length of the lines and the height of the people you will find that they are exactly the same. Your eyes are playing tricks on you.
Do you have any more questions about your eyes?
DrKim says
Sometimes what you see may look blurry or fuzzy. You may not be able to see things close to you or it may be hard to see things clearly if they are far away. Tell mum, dad, or the teacher about it.
Your eyes could be playing tricks or they could be asking you for some help.
We've collected this information to help you to understand important things about staying healthy and happy. However, if you feel sick or unhappy, it is important to tell your mum or dad, a teacher or another grown-up.