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Deafness

Deafness is a partial or complete loss of hearing that causes a person to be unable to understand speech and recognize environmental sounds even using a hearing aid. The medical condition of deafness is considered a disability, affecting from 3 to 10 of every 1,000 people in the United States. Language is the area of life most impacted by deafness. As famously observed by Helen Keller, who was both blind and deaf, deafness separates one from people because it precludes access to spoken language. In the minority Deaf community, where sign language is the primary language, deafness is viewed as a difference in the human experience that, although isolating from mainstream culture, is not a disability in need of a cure. This entry first describes the causes of deafness and then gives an overview of major life impacts of deafness, distinguishing between deafness that occurs in childhood, before language is learned, and deafness that develops in elderly adults. The discussion of childhood deafness focuses on how a deaf child can acquire language and includes an introduction to cochlear implants (CIs) as a treatment for deafness. The discussion of deafness in the elderly focuses on the effect of acquired deafness on the quality of life.

Causes of Deafness

Problems at various points along the auditory pathways from the outer ear to the brain can cause temporary or permanent deafness. Conductive deafness occurs when the outer and middle ear do not convey sound efficiently to the inner ear. Most cases of conductive hearing loss are temporary: The most common cause is inflammation of the middle ear, or otitis media, accompanying childhood ear infection. Sensorineural deafness begins at the inner ear, where mechanical sound waves are converted into neural signals, or at the auditory nerves that carry these signals to the brain. Sensorineural or nerve deafness is generally permanent and irreversible, although modern technologies that bypass the inner ear and deliver electrical signals directly to the auditory nerve can provide some ability to perceive sound in many cases.

Sensorineural deafness that is present at birth often has a genetic reason. Because the genes involved are usually recessive, it is typical for both parents of a deaf child to have normal hearing. Most genetic causes of deafness produce only deafness and no other symptoms. Complications with a pregnancy, including certain illnesses, premature birth, or drugs taken during pregnancy, can also cause deafness at birth. Sensorineural deafness that is acquired after birth can result from viral infection, head injury, very loud noise, or certain drugs that are toxic to the auditory system. Most frequently, acquired sensorineural deafness is associated with adult aging. A lifetime of cumulative exposure to noise created by an industrial society tends to cause hearing loss; and for some individuals who have genetic vulnerability, age-related hearing loss can progress to deafness.

Prelingual Deafness

Children who are born deaf or acquire deafness in their first years of life are considered prelingually deaf because their deafness happened before they learned a spoken language. Prelingual deafness is often identified by a newborn hearing screening. About 90% of children who are born deaf have parents who can hear normally. These deaf-of-hearing children face a unique problem of not having access to the language used in their family. To create a shared language environment from which to learn language, a deaf child needs a medical intervention followed by intensive training in spoken language, or their families need to learn sign language, or both. Building a shared medium of communication is difficult and time-consuming. Because of early auditory deprivation during critical periods of language acquisition, deaf-of-hearing children are usually delayed in acquiring language.

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