deafness - Categories of deafness and hearing impairment

Inability or reduced capacity to hear external sounds. Conductive deafness is caused by blockage of the entry of sound to the external canal of the ear (eg through wax in ear), or by abnormalities of the eardrum (tympanic membrane) or bones (ossicles) in the middle ear (eg through middle-ear infection). All sounds irrespective of their pitch are heard with difficulty, and if they are sufficiently loud or amplified they may become clearly heard. Sensorineural deafness results from a disturbance of the cochlea, auditory nerve, or neuronal pathways in the brain. Loss of hearing tends to be patchy, affecting only certain frequencies, and amplified or loud sounds are distorted. Causes include certain drugs and lengthy exposure to industrial noise, and it may also develop as a normal part of ageing.