Eyesight

Eyes are brilliant

In an average life, they'll see 24 million different images. They can focus quickly between distances of 10cm and infinity. We can see in bright sunlight and almost complete darkness and judge speed within 5-10% accuracy.

More of our brain is taken up with eyesight than any other bit of our body.

All this from a couple of balls only 2.5 cm in diameter.

What's normal vision?

If we have normal vision this is called 6/6 (or 20/20, before the world went metric). It means that we can see things 6 metres away that people with normal vision can also see at that distance. So 5/6 means we have to stand at 5 metres to see what normal sighted people manage to see at 6. Geddit?

How do eyes work?

Light goes into our eyes through the pupil. It hits the back of our eye (called the retina). Here light is detected by special cells called rods and cones. These send electrical impulses to our brain, telling it about the light. Cones detect colours, and accurate detail. Rods detect black and white shades, helpful for seeing at night.

Our brain puts all the impulses together to make a picture. Our eyes constantly move about, updating the brain with more information about what's going on.

So why have I got two eyes?

Each eye sees the world slightly differently. Hold your hand close to your face and look at it, closing each eye in turn. See?
Sending two simultaneous images to our brain helps us see things in 3D and judge distances more accurately.

What does short-sighted mean?

This means we have no problem seeing stuff close up. But far away things are blurry. We're the ones at the bus stop who can't see the bus number till it arrives. Long sighted means the opposite: Reading a book is harder than reading a street sign.
Either way, we might need glasses. About half of us need glasses, at some point.

What are those blobs I see floating in space?

When we look at the sky we may see specks or cobwebby strands drifting across our vision. These are called floaters. We are actually seeing an inner part of our eye moving. This is normal, as long as there isn't a rapid increase in the number of floaters. And we can still see properly.

How to have bright eyes for life:

Diet.
Eat five fresh fruit and veg every day. The more colourful the better. So think rainbows and chop up that fruit salad.

Sunglasses.
Make sure yours have proper UV protection.

Rest.
Staring at the TV or computer all day? Take a break every 15 minutes. Change the scenery.

Stop smoking.
Smoking causes blindness. Add that to the million other reasons you need to quit.

Eye Checks.
We should all have out eyes tested regularly, at least every five years. We should go more often if we've noticed changes to our eyesight. If we are under 16 or under 19 in full time education, the eye test is free. Ask your optician.
And if our eyes go red, sticky or painful - it's time to visit the doc. Same goes if we notice flashing lights or a rapid increase in floaters.

Other Eye Facts

Brown is the most common eye colour, blue the rarest (only 8% of the world's population has blue eyes).
Eyebrows protect our eyes from sweat running off our forehead. Over pluck at your peril.
Tears from crying are different to those we get in a cold wind, or from onions. No one knows for sure why we make tears when we're sad.
We blink about twelve times per minute. This keeps our eyes clean.

Further help and advice

Info from the NHS

Written by Dr Melissa Sayer

Last updated 17th June 2007

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