Hearing Impairment / Loss

Hearing loss, deafness, hard of hearing, hearing impairment, is a partial or total inability to hear.  In children it may affect the development of language and can cause work related difficulties for adults.

It is caused by many factors, including: genetics, aging, exposure to noise, illness, chemicals and physical trauma. Hearing testing may be used to determine the severity of the hearing loss. While the results are expressed in decibels, hearing loss is usually described as mild, mild-moderate, moderate, moderately severe, severe, or profound. Hearing loss is usually acquired by a person who at some point in life had no hearing impairment.

There are a number of measures that can prevent hearing loss and include avoidance of loud noise, chemical agents, and physical trauma. Testing for poor hearing is recommended for all newborns.  But, in some cases such as due to disease, illness, or genetics, it is impossible to reverse or prevent. Hearing aids are partially effective for many.

Globally hearing loss affects about 10% of the population to some degree.  It caused moderate to severe disability in 124 million people as of 2004 (108 million of whom are in low and middle income countries).  Of these 65 million developed the condition during childhood.  It is one of the most common medical conditions presenting to physicians.  It is viewed by some in the deaf community as a condition, not an illness. Treatments such as cochlear implants have caused controversy in the deaf community.

 
Diagnosis

The severity of a hearing impairment is ranked according to the additional intensity above a nominal threshold that a sound must be before being detected by an individual; it is (measured in decibels of hearing loss, or dB HL). Hearing impairment may be ranked as mild, moderate, moderately severe, severe or profound as defined below:

  • Mild:
    • for adults: between 26 and 40 dB HL
    • for children: between 20 and 40 dB HL
  • Moderate: between 41 and 54 dB HL
  • Moderately severe: between 55 and 70 dB HL
  • Severe: between 71 and 90 dB HL
  • Profound: 91 dB HL or greater
  • Totally Deaf: Have no hearing at all.

Hearing sensitivity varies according to the frequency of sounds. To take this into account, hearing sensitivity can be measured for a range of frequencies and plotted on an audiogram.

For certain legal purposes such as insurance claims, hearing impairments are described in terms of percentages. Given that hearing impairments can vary by frequency and that audiograms are plotted with a logarithmic scale, the idea of a percentage of hearing loss is somewhat arbitrary, but where decibels of loss are converted via a recognised legal formula, it is possible to calculate a standardised "percentage of hearing loss" which is suitable for legal purposes only.

Another method for quantifying hearing impairments is a speech-in-noise test. As the name implies, a speech-in-noise test gives an indication of how well one can understand speech in a noisy environment. A person with a hearing loss will often be less able to understand speech, especially in noisy conditions. This is especially true for people who have a sensorineural loss – which is by far the most common type of hearing loss. As such, speech-in-noise tests can provide valuable information about a person's hearing ability, and can be used to detect the presence of a sensorineural hearing loss. A triple-digit speech-in-noise test was developed by RNID as part of an EU funded project Hearcom. The RNID version is available over the phone, on the web and as an app on the iPhone.

 
Classification

Hearing impairments are categorised by their type, their severity, and the age of onset (before or after language is acquired). Furthermore, a hearing impairment may exist in only one ear (unilateral) or in both ears (bilateral). There are three main types of hearing impairments, conductive hearing impairment and sensorineural hearing impairment and a combination of the two called mixed hearing loss.

Conductive hearing loss
A conductive hearing impairment is present when the sound is not reaching the inner ear, the cochlea. This can be due to external ear canal malformation, dysfunction of the eardrum or malfunction of the bones of the middle ear. The ear drum may show defects from small to total resulting in hearing loss of different degree. Scar tissue after ear infections may also make the ear drum dysfunction as well as when it is retracted and adherent to the medial part of the middle ear.

Dysfunction of the three small bones of the middle ear – malleus, incus, and stapes – may cause conductive hearing loss. The mobility of the ossicles may be impaired for different reasons and disruption of the ossicular chain due to trauma, infection or anchylosis may also cause hearing loss.

Sensorineural hearing loss
A sensorineural hearing loss is one caused by dysfunction of the inner ear, the cochlea, the nerve that transmits the impulses from the cochlea to the hearing centre in the brain or damage in the brain. The most common reason for sensorineural hearing impairment is damage to the hair cells in the cochlea. Depending on the definition it could be estimated that more than 50% of the population over the age of 70 has impaired hearing.

Mixed hearing loss
Mixed hearing loss is a combination of the two types discussed above. Chronic ear infection (a fairly common diagnosis) can cause a defective ear drum or middle-ear ossicle damages, or both. Surgery is often attempted but not always successful. On top of the conductive loss, a sensory component is often added. If the ear is dry and not infected, an air conduction aid could be tried; if the ear is draining, a direct bone condition hearing aid is often the best solution. If the conductive part of the hearing loss is more than 30–35 dB, an air conduction device could have problems overcoming this gap. A direct bone conduction aid like the Baha or the Ponto could, in this situation, be a good option.

 
Management

There are a number of devices that can improve hearing in those who are hearing impaired or deaf or allow people with these conditions to manage better in their lives.

 
Assistive devices

Many hearing impaired individuals use assistive devices in their daily lives:

  • Individuals can communicate by telephone using telecommunications device for the deaf (TDD). These devices look like typewriters or word processors and transmit typed text over regular telephone lines. Other names in common use are textphone and minicom.
  • There are several new telecommunications relay service technologies including IP Relay and captioned telephone technologies. A deaf or hard of hearing person can communicate over the phone 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.
  • Real-time text technologies, involving streaming text that is continuously transmitted as it is typed or otherwise composed. This allows conversational use of text. Software programs are now available that automatically generate a closed-captioning of conversations. Examples include discussions in conference rooms, classroom lectures, and/or religious services. One such example of an available product is Auditory Sciences'Interact-AS product suite.
  • Instant messaging software. In addition, AOL Instant Messenger provides a real-time text feature called Real-Time IM.
  • Videophones and similar video technologies can be used for distance communication using sign language. Video conferencing technologies permit signed conversations as well as permitting a sign language–English interpreter to voice and sign conversations between a hearing impaired person and that person's hearing party, negating the use of a TTY device or computer keyboard.
  • Video relay service and video remote interpreting (VRI) services also use a third-party telecommunication service to allow a deaf or hard-of-hearing person to communicate quickly and conveniently with a hearing person, through a sign language interpreter.
  • Phone captioning is a service in which a hearing person's speech is captioned by a third party, enabling a hearing impaired person to conduct a conversation with a hearing person over the phone.
  • For mobile phones, software apps are available to provide TDD/textphone functionality on some carriers/models to provide 2-way communications.
  • Other assistive devices include those that use flashing lights to signal events such as a ringing telephone, a doorbell, or a fire alarm.
  • 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 reduced the need for deaf and hard-of-hearing people to use a third-party Telecommunications Relay Service to communicate with the hearing and other hearing impaired people.
 
Wireless devices

A wireless device has two main components: a transmitter and a receiver. The transmitter broadcasts the captured sound, and the receiver detects the broadcast audio and enables the incoming audio stream to be connected to accommodations such as hearing aids or captioning systems.

Three types of wireless systems are commonly used: FM, audio induction loop, and InfraRed. Each system has advantages and benefits for particular uses. FM systems can be battery operated or plugged into an electrical outlet. FM system produce an analog audio signal, meaning they have extremely high fidelity. Many FM systems are very small in size, allowing them to be used in mobile situations. The audio induction loop permits the listener with hearing loss to be free of wearing a receiver provided that the listener has a hearing aid or cochlear implant processor with an accessory called a "telecoil". If the listener does not have a telecoil, then he or she must carry a receiver with an earpiece. As with FM systems, the infrared (IR) system also requires a receiver to be worn or carried by the listener. An advantage of IR wireless systems is that people in adjoining rooms cannot listen in on conversations, making it useful for situations where privacy and confidentiality are required. Another way to achieve confidentiality is to use a hardwired amplifier, which contains or is connected to a microphone and transmits no signal beyond the earpiece plugged directly it.

 

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