Impairment of hearing, which affects about 2 million adults in the UK.
In most people, deafness is a result of sensorineural hearing impairment (nerve deafness). This means that the abnormality is in the inner ear (the cochlea), in the auditory nerve, or in the brain itself. The prevalence of this type of hearing impairment rises greatly in elderly people, to the extent that more than 50 per cent of the over-70s have a moderate hearing impairment. In most cases no definite cause can be found, but contributory factors include excessive exposure to noise, either at work (e.g. shipyards and steelworks) or at leisure (loud music). Military personnel exposed to gunfire or explosions are also at risk of hearing impairment.
Conductive hearing impairment is the other main classification. Here there is an abnormality of the external or middle ear, preventing the normal transmission of sound waves to the inner ear. This is most commonly due to chronic otitis media where there is long-standing inflammation of the middle ear, often with a perforation of the ear drum. It is thought that in the majority of cases this results from childhood middle-ear disease. Many preschool children suffer temporary hearing loss because of otitis media with effusion (glue ear). Wax does not interfere with hearing unless it totally obstructs the ear canal or is impacted against the tympanic membrane. In infants, permanent deafness is much less common: about 1–2 per 1,000. It is essential, however, that deafness is picked up early so that appropriate treatment and support can be given to improve hearing and/or ensure that the child can learn to speak. (See also EAR; EAR, DISEASES OF.)
Conductive hearing impairment can, in many cases, be treated the use of a hearing aid or by an operation on the middle ear. Sensorineural hearing impairments can be treated only with a hearing aid. In the UK, hearing aids are available free on the NHS. Most NHS hearing aids are ear-level hearing aids – that is, they fit behind the ear with the sound transmitted to the ear via a mould in the external ear. Smaller hearing aids are available, particularly from the private sector, which fit within the ear itself, and people can wear such aids in both ears. Some of these are very sophisticated, only amplifying the particular sound wavelengths with which the person has difficulty. The use of certain types of hearing aid may be augmented by fittings incorporated into the aid which pick up sound directly from television sets or from telephones, and from wire loop systems in halls, lecture theatres and classrooms. People with hearing impairment should seek audiological or medical advice before purchasing any of the many types of hearing aid available commercially. Those people with a hearing impairment which is so profound that they cannot be helped by a hearing aid can sometimes now be fitted with an electrical implant in their inner ear (see COCHLEAR IMPLANTS).
Congenital hearing loss accounts for a very small proportion of the hearing-impaired population. It is important to detect this at an early stage as, if undetected and unaided, it may lead to delayed or absent development of speech. Otitis media with effusion (glue ear) usually resolves spontaneously, although if it persists, surgical intervention has been the traditional treatment involving insertion of a ventilation tube (see GROMMET) into the ear drum, often combined with removal of the adenoids (see NOSE, DISORDERS OF). However, these operations usually provide only transient relief and probably make no difference to long-term outcome.