2 Clinical need and practice
2.1 Hearing loss may be caused by interference with the transmission of sound from the outer to the inner ear (conductive hearing loss) or damage within the cochlea, the auditory nerve or auditory centres in the brain (sensorineural hearing loss). In adults the most common cause of sensorineural hearing loss is presbycusis. This is a progressive condition caused by the loss of function of hair cells in the inner ear, leading to deafness. Hearing loss in adults may also be caused by excessive exposure to noise, or by ototoxic drugs, metabolic disorders, infections or genetic factors. Severe to profound hearing loss in children may have a genetic aetiology, or have prenatal, perinatal or postnatal causes. These include conditions such as meningitis and viral infection of the inner ear (for example, rubella or measles), as well as premature birth and congenital infections. Deafness that occurs before the development of language is described as prelingual, whereas deafness that occurs after the development of language is described as postlingual.
2.2 Approximately 370 children in England and 20 children in Wales are born with permanent severe to profound deafness each year. Approximately 90% of these children have two parents who can hear. About 1 in every 1000 children is severely or profoundly deaf at 3 years old. This rises to 2 in every 1000 children aged 9 to 16 years. There are approximately 613,000 people older than 16 years with severe to profound deafness in England and Wales. In the UK around 3% of people older than 50 and 8% of those older than 70 years have severe to profound hearing loss. Approximately 40% of children who are deaf and 45% of people younger than 60 years who are deaf have additional difficulties, such as other physical disabilities.
2.3 Deafness is not typically associated with increased mortality, and need not be associated with significant morbidity. Some people who are deaf identify with a cultural model of deafness in which deafness is not considered an impairment. These people, who often use sign language as their preferred language and grow up as members of the 'Deaf community', may not perceive deafness to have a major impact on their quality of life. However, for a child who is born deaf within a hearing family or for a person who becomes deaf and is used to functioning in a hearing environment, deafness can have a significant impact on their quality of life. For children, deafness may have significant consequences for linguistic, cognitive, emotional, educational and social development. Loss of hearing affects an adult's ability to hear environmental noises and to understand speech; this can affect their ability to take part in their daily activities and be part of their usual social and professional networks, which can lead to isolation and mental health problems.
2.4 Services for people who are deaf aim to improve their quality of life by maximising their ability to communicate, using the means most appropriate for the person and their environment, and to enable the person to move safely within their environment. There are approximately 50,000 people in the UK who communicate using British Sign Language. These are generally people who were born deaf or became deaf shortly after birth. Most people who are deaf use oral and aural communication supplemented by lip reading, cued speech (visual cues to clarify the sounds of English), signs (finger spelling or sign-supported English) and the written word. Regardless of the chosen means of communication, people may also use powerful hearing aids to help them identify environmental noises and to hear spoken language. However, for some people there are too few functioning hair cells for hearing aids to be of use.
2.5 National frameworks covering audiology include the NHS Newborn Hearing Screening Programme and the NHS Modernising Hearing Aid Services programme for children and adults. The NHS Newborn Hearing Screening Programme screens all newborn babies within 26 days of birth for possible hearing difficulties. Babies who at screening are identified as having possible hearing difficulties are referred to NHS audiology services. Those who are then confirmed deaf should receive a hearing aid within 2 months. This initial diagnosis is followed by ongoing support, which includes regular audiological assessment and consideration of the appropriateness of a cochlear implant (usually within the first year). Hearing services for adults are coordinated by audiology departments and normally include a review every 4 years, although this varies across the UK.
2.6 Potential candidates for cochlear implants are referred to one of the cochlear implant centres in England and Wales, where they receive a multidisciplinary assessment to determine whether they are suitable for cochlear implantation. Both audiological hearing and functional hearing are assessed as part of the multidisciplinary assessment, as well as other factors such as fitness for surgery, structure of the cochlea, the presence of a functioning auditory nerve and the likely ability of the person to derive benefit from the stimuli produced by the cochlear implant system.
2.7 Audiological testing identifies the additional intensity that a pure tone sound must possess to be detected relative to the intensity that can be detected by young adults without hearing impairment. Guidelines from the British Cochlear Implant Group suggest that people who cannot hear sounds quieter than an average of 90 dB HL when tested at frequencies of 2 and 4 kHz without acoustic hearings aids would be considered for cochlear implantation if they do not derive adequate benefit from acoustic hearing aids.
2.8 Functional hearing is tested with optimum acoustic hearing aids and focuses on a person's ability to perceive speech. For adults, functional hearing is usually assessed using Bamford–Kowal–Bench (BKB) sentences. Guidelines from the British Cochlear Implant Group state that an adult who identifies 50% or more of keywords at a sound intensity of 70 dB SPL in quiet conditions is considered to be deriving an adequate benefit from their hearing aids. Functional hearing in children is assessed through the development and maintenance of speech, language, communication and listening skills that are appropriate for the age, developmental stage and cognitive ability of the child. For this reason no single test is used.
2.9 During the year ending March 2007, 374 adults and 221 children had unilateral cochlear implantations in England and 8 adults and 22 children in Wales. A further 451 adults and 446 children were under assessment. In the UK, in the year ending March 2007, 32 bilateral implantations were performed in children and 11 in adults. A survey of 15 of the 18 cochlear implant centres in England and Wales showed that 704 children and adults had received a unilateral cochlear implant during the financial year ending March 2008. In addition, there were 77 children and adults who had received bilateral cochlear implants. Of these, 39 were simultaneous implants and 38 were sequential implants.