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| The Human Body Page 4 |
Q. 31. What is the spleen?
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Q. 32. What gives our eyes their colour?
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Q. 33. Why can't we see colours in the dark?
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Q. 34. What causes blindness?
Ans. Did you know that there are at least fourteen million blind people in the world? There are many degrees of blindness, making it challenging to define blindness. Some people cannot even see light. Others can only tell light from dark. Still others have a small amount of vision.
Of all the blind people in the world, only a small percentage were born blind. Blindness at birth is called congenital blindness. The causes of it are not all known.
Blindness that occurs after birth is caused mainly by diseases of the eyes. A general disease of the body, such as diabetes or meningitis, rather than a disease of the eye itself, may also cause blindness. Accidents and explosions are two other causes of blindness.
In countries where people live longer because of good medical care and a high standard of living, old age often brings on certain eye conditions. Two of these eye conditions are cataracts and glaucoma. Cataracts are among the leading causes of blindness.
A cataract is a clouding of the lens of the eye. The lens, the transparent part of the eye through which light rays pass, becomes cloudy, and only strong light rays can pass through it. There is consequently a loss of vision. Cataracts can be removed by surgery.
With glaucoma, there is a hardening of the eyeball and great pressure inside the eye. Today, there are medicines to control glaucoma if it is discovered in time.
The greatest single cause of loss of sight is trachoma. It is a contagious disease of the eyes caused by a virus. It affects the inner linings of the eyelids. Also, blood vessels grow over the cornea.
Antibiotics can now control trachoma, but it is still common in some parts of Europe, Africa, and Asia.
Related queries:
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Q. 36.
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Q. 37.
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Q. 38.
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Q. 39.
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Q. 40.
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Continued to page 5
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