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Hearing Device Options

Atresia and Microtia can cause up to a 60 dB conductive hearing loss. Since this is the level of a fairly loud conversation, it is important to have the person’s exact amount of loss determined through audiological testing, and then decide whether an assistive hearing device is required.

The two primary forms of assistive hearing devices for people with Atresia and/or Microtia are BCHAs (Bone Conduction Hearing Aids) and BAHAs (Bone Anchored Hearing Aids).

Bone Conduction Hearing Aids

A bone conduction hearing aid is different from a conventional hearing aid. Conventional hearing aids amplify sound and pass it through the earmold, into the ear canal, through the middle ear and to the inner ear. These hearing aids can’t be used by people with atresia, as the ear canal is not present so sound cannot get through. The sound must be transmitted in a different manner, through the bone.

A bone conduction hearing aid sends a signal travels through a wire leading to an oscillator, which vibrates. When this oscillator is placed against the skull (usually behind the ear on the mastoid bone), the sound vibration is carried through the skull bone to both inner ears.

As with any hearing aid, the quality of sound from a bone conduction hearing aid is not perfect. Both the dynamic range and the frequency range are limited, resulting in sound similar to listening through a telephone. Another disadvantage, which is specific to hearing by "bone conduction," is that the listener hears in "mono." When the bone is vibrated in any location, the sound travels to both inner ears at almost the same time. This causes significant difficulty in determining the location of the source of a sound.

Bone Conduction Hearing Aids can be worn either with a rigid metal headband or a soft headband. The choice is primarily based on the age of the child and their comfort preference.

The two main manufacturer’s of BCHAs are
http://www.starkey.com
http://www.oticon.com

BAHA® (Bone Anchored Hearing Aids)

The BAHA, Bone Anchored Hearing Aid, was developed in Sweden, and has been used widely in Europe for many years with great success. It has been offered in North America for many years for adults, but it was only recently that its use has been accepted for children. The BAHA® hearing aid makes use of a titanium "abutment" that must be surgically implanted behind the patient’s ear. The hearing aid clips onto this abutment, and transmits the sound by bone conduction, just like a conventional BCHA (discussed above) . The advantage is that the vibration is transmitted directly to the bone, instead of through the skin.

Even more recent is the advent of Bilateral BAHA® implantation. This has recently been approved by the FDA, which means some insurance companies will now cover the procedure. Studies show bilateral BAHA fittings help in noisy situations, and enable the wearer to localize sounds, even when they have used a monaural bone conduction aid all of their lives.

This direct contact translates into several advantages: a lower power hearing aid can be used, the direct connection reduces distortion in the sound, and a wider frequency range can be produced. If we say the bone conduction aid sounds like a telephone, then the BAHA® would sound more like a good quality FM radio (tuned into a clear station of course). Disadvantages include the requirement for surgery, the potential for skull fracture due to blows to the BAHA®.

Pictures from the Entific Web Site

The Patients BAHA web site http://www.patients-baha.com
Entific — a company that manufactures the BAHA http://www.entific.com
Bone Conduction Phones:
http://www.globe-mart.com/comm/phones/specialneeds/MIRAFONE.htm
http://www.temco-j.co.jp/html/English/HG16.html

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