Impairment of hearing is generally called deafness. It is caused by any interference with the reception or transmission of sound waves along the canal through the middle ear to the inner ear and then along the auditory nerve to the brain. Deafness is either congenital or caused by some disease or accident after the birth.
The congenital deafness can be caused by many different factors. For example, if a pregnant woman suffers from measles within three months of conception, the child born can be deaf. At least 50% of such women have been found to be giving birth to deaf children.
However, in many cases deafness occurs after the birth. In such cases sound waves are not able to reach the eardrum because they get obstructed by the deposition of a waxy substance on the eardrum. You might have noticed the formation of a brown coloured waxy substance inside the ears. This regularly comes out of the ear in small bits. In some cases this material is deposited on the eardrum. As a result of this sound waves get reflected back and are unable to reach the eardrum. In another case, the internal nerves of the ear get burst due to some injuries or very intense sounds and consequently the ear is unable to hear any sound.
The people who live in very noisy areas also get their hearing power impaired. They are able to hear only loud sounds. In the Second World War, 58,000 soldiers developed deafness because of the fierce sounds of tanks and machine guns. Deafness can be caused by ear diseases also. Sometimes due to the bad effects of the diseases in other parts of the body also cause deafness. Even aging reduces the power of hearing. Excessive use of some intoxicating medicines can also affect the power of hearing. At times undesirable growth of some bones inside the ear also causes deafness because these prevent the sound waves from reaching the main parts of the ear.
Today sophisticated instruments are available by which one can hear feeble sounds. Such instruments are known as ‘hearing-aids’. In some cases surgery is also helpful in the treatment of deafness.