What is colour blindness?
True colour blindness is when people cannot see any colour at all, but it is very rare. More commonly, many people cannot see true colours accurately. The most common form is red-green colour blindness, where people find it difficult to distinguish between red, green and brown. It affects about one in every 12 men, but is less common in women.
Colour blindness is measured using special charts in which patterns are made up with coloured dots. A person who has a colour defect will see these patterns in a totally different way to someone who has perfect colour vision.
Why do some people need glasses?
If the eye is not exactly the right shape, or the lens cannot focus properly, you cannot form a clear image on the retina. In this case you may need to wear glasses to correct your vision. For a short-sighted person, distant objects look blurred because the image forms in front of the retina. A short-sighted person can see nearby objects very clearly. For a long-sighted person, the image tries to form behind the retina, so it is blurred while the lens tries to focus on a nearby object.
In another sight problem, called astigmatism, the cornea is not evenly curved and vision is distorted. The different sight problems can be overcome with the use of glasses.
Pictures Credit: Google