Did you know that there are at least fourteen million blind people in the world? Of all blind people in the world, only a small percentage was born blind. Blindness at birth is called congenital blindness. The causes of it are not all known. Mainly diseases of eyes cause blindness that occurs after birth. 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 cataract and glaucoma. Cataract is one of 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 ray can pass through it. There is consequently a loss in 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 sight is trachoma. It is a contagious disease of the eyes caused by a virus. If affects the inner lining of the eyelids. Also, blood vessels grow over the cornea. This can destroy the vision. Antibiotics can now control trachoma, but it is still common in some parts of Europe, Africa and Asia.