Hearing impairment

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Hearing impairment
ICD-10 code: H90-H91
ICD-9 code: 389
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This article is a physical description of hearing impairment. See deaf culture for deafness as a cultural view.

A hearing impairment is a decrease in one's ability to hear (i.e. perceive auditory information). While some cases of hearing loss are reversible with medical treatment, many lead to a permanent disability (often called deafness).

If the hearing loss occurs at a young age, it may interfere with the acquisition of spoken language. Hearing aids and cochlear implants may alleviate some of the problems caused by hearing impairment, but are often insufficient. People who have hearing impairments, especially those who develop a hearing problem later in life, often require support and technical adaptations as part of the rehabilitation process.

Contents

Causes

There are four major causes of hearing loss: genetic, disease processes affecting the ear, medication and physical trauma.

Genetic

Hearing loss can be inherited. Both dominant and recessive genes exist which can cause mild to profound impairment. If a family has a dominant gene for deafness it will persist across generations because it will manifest itself in the offspring even if it is inherited from only one parent. If a family had genetic hearing impairment caused by a recessive gene it will not always be apparent as it will have to be passed onto offspring from both parents.

Dominant and recessive hearing impairment can be syndromic or nonsyndromic. Recent gene mapping has identified dozens of nonsyndromic dominant (DFNA#) and recessive (DFNB#) forms of deafness.

Disease or illness

  • Measles may result in auditory nerve damage
  • Meningitis may damage the auditory nerve or the cochlea
  • Autoimmune disease has only recently been recognised as a potential cause for cochlear damage. Although probably rare, it is possible for autoimmune processes to target the cochlea specifically, without symptoms affecting other organs. Wegener's granulomatosis is one of the autoimmune conditions that may precipiate hearing loss.
  • Presbyacusis is deafness due to loss of perception to high tones, mainly in the elderly. It is considered a degenerative process, and it is poorly understood why some elderly people develop presbyacusis while others do not.
  • Mumps (Epidemic parotitis) may result in profound sensorineural hearing loss (90 dB or more), unilateral (one ear) or bilateral (both ears).
  • Adenoids that do not disappear by adolescence may continue to grow and may obstruct the Eustachian tube, causing conductive hearing impairment and nasal infections that can spread to the middle ear.
  • AIDS and ARC patients frequently experience auditory system anomalies.[1]
  • HIV (and subsequent opportunistic infections) may directly affect the cochlea and central auditory system.[2]
  • Chlamydia may cause hearing loss in newborns to whom the disease has been passed at birth.[3]
  • Fetal alcohol syndrome is reported to cause hearing loss in up to 64% of infants born to alcoholic mothers, from the ototoxic effect on the developing fetus plus malnutrition during pregnancy from the excess alcohol intake.[4]
  • Premature birth results in sensorineural hearing loss approximately 5% of the time.[5]
  • Syphilis is commonly transmitted from pregnant women to their fetuses, and about a third of the infected children will eventually become deaf.[6]
  • Otosclerosis is a hardening of the stapes (or stirrup) in the middle ear and causes conductive hearing loss.

Medications

Some medications cause irreversible damage to the ear, and are limited in their use for this reason. The most important group is the aminoglycosides (main member gentamycin).

Various other medications may reversibly affect hearing. This includes some diuretics, aspirin and NSAIDs, and macrolide antibiotics.

Physical trauma

  • There can be damage either to the ear itself or to the brain centers that process the aural information conveyed by the ears.
  • People who sustain head injury are especially vulnerable to hearing loss or tinnitus, either temporary or permanent.
  • Exposure to very loud noise (90 dB or more, such as jet engines at close range) can cause progressive hearing loss. Exposure to a single event of extremely loud noise (such as explosions) can also cause temporary or permanent hearing loss.

Noise Exposure

  • Noise-induced hearing loss is the second most common form of sensorineural hearing deficit, after presbycusis (age-related hearing loss)
  • Exposure to high levels of noise (>85 dB or more) for extended periods of time can cause a permanent, sensorineural hearing loss.
  • Noise-Induced Hearing Loss (NIHL) typically begins at 4,000 Hz and spreads downward and upward.
  • Earplugs or earmuffs can help to reduce the noise that reaches the ear.
  • The louder the noise is, the shorter the safe amount of exposure is. For example, the safe exposure amount at 85 dB is 8 hours, while the safe exposure at 90 dB is only 2 hours, 31 minutes (National Institute for Occupational Safety and Health, 1998)
  • Personal electronic audio devices, such as iPods, can produce powerful enough sound to cause significant Noise-Induced Hearing Loss

Categories of hearing impairment

Hearing loss is catagorized by its severity and by the age of onset. Two persons with the same severity of hearing loss will experience it quite differntly if it occurs early or late in life. Furthermore, a loss can occur on only one side (unilateral) or on both (bilateral).

Types

There are three major types of hearing loss: neural/sensorineural, conductive, or a combination of both. Treatment depends upon the type of hearing loss that is present.

Sensorineural

Sensorineural hearing loss is caused by damage/malfunction of the inner ear (cochlea, eighth cranial nerve) or auditory brainstem. This can be divided further into a sensory hearing loss (inner ear) or a neural hearing loss (brainstem).

Conductive

Conductive hearing loss is caused by damage/malfunction of the middle or outer ear system (external ear canal, ear drum, or structures in the middle ear space including the malleus, incus and stapes bones).

Combination

Mixed hearing loss is caused by both conductive and sensorineural causes.

Quantification of hearing loss

The severity of hearing loss is measured by the degree of loudness, as measured in decibels, a sound must attain before being detected by an individual. Hearing loss may be ranked as mild, moderate, severe or profound. It is quite common for someone to have more than one degree of hearing loss (i.e. mild sloping to severe). The following list shows the rankings and their corresponding decibel ranges:

  • Mild:
    • for adults: between 25 and 40 dB
    • for children: between 15 and 40 dB
  • Moderate: between 41 and 55 dB
  • Moderately severe: between 56 and 70 dB
  • Severe: between 71 and 90 dB
  • Profound: 90 dB or greater

Pre- or postlingual

The age at which the hearing impairment develops is crucial to spoken language acquisition. Post-lingual hearing impairments are far more common than pre-lingual impairments.

Pre-lingual deafness

Main article: Prelingual deafness

Prelingual hearing impairment exists when the impairment is congenital or otherwise acquired before the individual has acquired speech and language, thus rendering the disadvantages more difficult to treat because the child is unable to access audible /spoken communication from the outset. It is important to note that those children born into signing families have no delay in language development and communication. Most pre-lingual hearing impairment is due to an acquired condition, usually either disease or trauma therefore families commonly have no prior knowledge of deafness.

Post-lingual hearing impairment

Main article: Post-lingual hearing impairment

Post-lingual hearing impairment where hearing loss is adventitious after the acquisition of speech and language, usually after the age of six. It may develop due to disease, trauma, or as a side-effect of a medicine. Typically, hearing loss is gradual, and often detected by family and friends of the people so affected long before the patients themselves will acknowledge the disability. Common treatments includes hearing aids and learning lip reading. Loneliness and depression can arise as a result of isolation (from the inability to communicate with friends and loved ones) and difficulty in accepting their disability.

Hard-of-hearing

People who are hard-of-hearing have moderate amounts of hearing loss but not enough to be considered deaf.

The phrase hard-of-hearing, normally used as an adjective or adverb, can also be used as a noun, referring to people with hearing impairment as the hard-of-hearing. People who consider themselves culturally deaf, prefer the term "hard-of-hearing" or "deaf", and perceive "hearing impaired" as an insult.

Hearing impaired persons with partial loss of hearing may find that the quality of their hearing varies from day to day, or from one situation to another or not at all. They may also, to a greater or lesser extent, depend on both hearing-aids and lip-reading. They may perhaps not always be aware of it, but they do admit to it being important to see the speaker's face in conversation.

Many people with hearing loss have better hearing in the lower frequency ranges (low tones), and cannot hear as well or at all in the higher frequencies.Some people may merely find it difficult to differentiate between words that begin with consonantal sounds such as the fricatives or sibilants, z, or th, or the plosives d, t, b, or p. They may be unable to hear thin, high-pitched or metallic noises, such as birds chirping or singing, clocks ticking, etc. Often, they are able to hear and understand men's voices better than women's.

Others will find their condition so much worse if circumstances in their immediate environment affect the way they are able to use their hearing-aids, or prevent them from employing their lip-reading skills. A room with a high ceiling and a lot of reverberation will affect the sound of a speaker's voice adversely. The position of the listener, too, sitting at a right angle to the speaker at a long seminar table, thus being able to hear only with one, maybe the ineffectual ear, can make a difference. Difficulties can also arise for the listener trying to lip-read, if the speaker is sitting with his back against the light-source and is in this way obscuring his face. A rule of thumb is that bright lighting is to the hearing-impaired what noise is to the hearing; a source of distraction.

The speaker's accent; the topic under discussion, possibly with many unfamiliar words; the softness of his voice; possibly his having a speech impediment; a habit of holding a hand in front of his mouth or turning his face away at times: all these tendencies cause problems to the hard-of-hearing, especially when they have to rely on lip-reading. The rustling of papers, and notebook pages being turned are precisely the noises that will be the first thing hearing-aids pick up.

Unilateral hearing loss

People with unilateral hearing loss (single sided deafness/SSD) can hear normally in one ear, but have trouble hearing out of the other ear. Problems with this type of deficit is inability to localize sounds (ie. unable to tell where traffic is coming from) and inability to process out background noise in a noisy environment, such as in a restaurant.

Social impact

Pre-lingual Impairment

In children, hearing loss can lead to social isolation for several reasons. First, the child experiences delayed social development that is in large part tied to delayed language acquisition. It is also directly tied to their inability to pick up auditory social cues. A child who uses sign language and is deaf, or identifies with the deaf sub-culture does not generally experience this isolation, particularly if he attends a school for the deaf, but may conversely experience isolation from his parents if they do not know sign language. A child who is exclusively or predominantly oral (using speech for communication) will experience social isolation from her hearing peers, particularly if no one takes the time to explicitly teach her social skills that other children acquire independently by virtue of having normal hearing. Finally, a child who has a severe impairment and uses some sign language may be rejected by her deaf peers, because of her understandable hesitation in abandoning the use of her verbal and speech-reading skills. The deaf community views this hesitation as a rejection of their own culture and its mores, and therefore will reject her out of self-defense.

Post-Lingual Impairment

Those who lose their hearing later in life, such as in late adolescence or adulthood, face their own challenges. For example, they must adjust to living with the adaptations that make it possible for them to live independently. They may have to adapt to using hearing aids or a cochlear implant, develop speech-reading skills, and/or learn sign language. The affected person may need to use a TTY (teletype), interpreter, or relay service to communicate over the telephone. Loneliness and depression can arise as a result of isolation (from the inability to communicate with friends and loved ones) and difficulty in accepting their disability. The challenge is made greater by the need for those around them to adapt to the person's hearing loss.

Medical treatments

Approaches

In addition to hearing aids there exist cochlear implants of increasing complexity and effectiveness. These are useful in treating the mild to profound hearing impairment when the onset follows the acquisitions of language and in some cases in children whose hearing loss came before language was acquired. Recent research shows variations in effacacy but some promising studies[7] show that if implanted at a very young age, some profoundly impaired children can acquire effective hearing and speech.

Views of treatments

There is controversy in the culturally deaf community as to whether cochlear implants address wellness concerns, the overall health and psycho-emotional well-being of prelingually deaf children at all.

Adaptations to hearing impairment

Many hearing impaired individuals use certain assistive devices in their daily lives. Individuals can communicate by telephone using telecommunications devices for the deaf (TDD) This device looks like a typewriter or word processor and transmits typed text over the telephone. Other names in common use are textphone and minicom. In 2004, mobile textphone devices came onto the market for the first time allowing simultaneous two way text communication. In the U.S., the UK, the Netherlands and many other western countries there are telephone relay services so that a hearing impaired person can communicate with a hearing person via a human translator. Wireless, internet and mobile phone/SMS text messaging are beginning to take over the role of the TDD. Other assistive devices include those that use flashing lights to signal events such as a ringing telephone, a doorbell, or a fire alarm. Video conferencing is also a new technology that permits signed conversations as well as permitting an ASL-English interpreter to voice and sign conversations between a hearing impaired and hearing person, negating the need to use a TTY or computer keyboard.

Resources

There are many different assistive technologies such as hearing aids available to people who are hearing impaired. There are also Hearing dogs which are a category of Assistance dogs. The advent of the internet's World-Wide-Web and closed captioning has given the hearing impaired unprecedented access to information. Electronic mail and online chat have virtually eliminated the need for hearing impaired people to use a third-party Telecommunications Relay Service in order to communicate with the hearing and other hearing impaired people.

How to communicate

Some guidelines on communicating with a hearing-impaired person:

  1. Ask the person what will be most useful for them; this varies from one individual to another. Not all items on this list will apply for all individuals. Most likely, the person will appreciate that you are communicating with their needs in mind and not stereotyping them according to often-expressed common preconceptions of hearing impairment.
  2. If the person uses sign language to communicate, take a class in sign language (possibly with the individual or along with family and friends). Show your support by striving to master the language. Don't be afraid to use an interpreter or write things down when you cannot communicate.
  3. Speak clearly and loudly, but do not shout or over-enunciate. Both of these make it more difficult to understand speech, not less.
  4. Do not mumble, cover your mouth, or whisper when speaking. All of these can conceal vital speech-reading cues that hearing impaired people use to decipher what is being said. A "favorite" pet peeve of the hearing impaired is people who speak from another room - How are they to speech-read with a wall between them and the speaker? Additionally, speak while facing the hearing impaired person.
  5. If asked to repeat yourself, remember that it is often more beneficial to rephrase instead. By using different words, your friend will be able to use two data sets to understand what you meant. (This is good advice for those with normal hearing, too!) Obviously, if only one word was missed, you can try just repeating that word, or a synonym. However, some hearing-impaired people would prefer that you repeat exactly instead of rephrasing; when a sentence is repeated, they can put together the syllables or words they heard the first time with those in the repetition. It is best to use the technique that the hearing-impaired person most prefers.
  6. Emphasize keywords in your phrases. Most hearing-impaired people can piece together keywords (along with the context of the conversation) into a statement that they can understand.
  7. Reduce background noise by turning off the TV and radio, and closing windows. All of these can provide distractions that cause communication to break down completely. They also impede the perception of whatever auditory cues your friend is able to pick up and use.
  8. For small children learning to talk, use context to help them decipher what you are saying. Use full sentences and refer to objects by their names. (Additionally, some studies indicate that hearing impaired children who are allowed to lead conversation acquire speech much more successfully than those whose parents attempt to guide conversation for them.)

See also

Quotations

  • "Blindness cuts you off from things; deafness cuts you off from people." -- Helen Keller
  • "What matters deafness of the ear, when the mind hears. The one true deafness, the incurable deafness, is that of the mind." -- Victor Hugo
  • "Deaf people can do anything except hear.". -- I. King Jordan

External links

Retrieved from "http://en.freepedia.org/Hearing_impairment.html"


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