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Behind The Ear Hearing AidsThe microphone is at the top of the hearing aid and the battery, amplifier and receiver are all inside the plastic case. Advantages:
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Back to Top In The Ear Hearing AidsAdvantages:
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Back to Top In The Canal Hearing AidsAdvantages:
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Back to Top Body Worn Hearing AidsAdvantages:
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Back to Top Bone Conduction Hearing AidsBone conduction hearing aids are therefore used by much less that 1% of hearing aid users. Indeed bone conduction aids are very often used because there is no alternative and not because they are necessarily capable of giving the best performance. It should be remembered that bone conduction vibrators will excite both ears about equally no matter which side they are placed. In essence the bone conduction hearing aid is identical to an air conduction aid apart from its output where a bone vibrator is used in place of an earphone. However, the use of a bone vibrator places a number of requirements on the design of the hearing aid and limits the type of aid that can be worn; spectacle, headband or bone anchored aid. The Bone VibratorThe bone vibrator is mounted on a headband which must exert pressure on the head in order to maintain a good contact. A reduction in pressure is likely to produce a considerable falling off in the effectiveness of the device. The major problem with bone conduction is keeping the vibrator applied without causing discomfort.It is normally worn behind the ear on the hairless part of the skull known as the 'mastoid process.' The effect may alter with quite small changes in position. They can be placed elsewhere on the head but there can be significant reduction in the level of sound perceived. This may not be a problem if the conductive hearing loss is such that there is sufficient power in the hearing aid to counteract this loss without undue distortion. Bone vibrators, like earphones, are designed with electrical characteristics to match the outputs of specific hearing aids, therefore care has to be taken as to which particular bone vibrator is used. Manufacturers and suppliers will be able to recommend the appropriate vibrator. Body Worn AidsA body worn aid for use with a bone vibrator has to be of the high powered type due to the much higher power requirements compared with the air conduction earphone. Most high powered body worn aids will work satisfactorily with an appropriate bone vibrator.
Post Aural and In-the-Ear AidsThe normal manufacturers range of post aural and in-the-ear aids are designed solely for air conduction and cannot be purchased as bone conduction aids.Spectacle Hearing AidsSpectacles provide an ideal way for the bone vibrator to be held in place in an inconspicuous manner with the minimum discomfort.The most widely available type is where the vibrator is housed in the back of the curved part of the arm of the spectacles and the microphone, battery and amplifier in the rest of the side arm. In some cases an aid can then be worn on both sides and in others, particularly with the more powerful aids, the amplifier is housed in the second arm. Spectacle aids of this type are expensive and require the cooperation of an optician and the hearing aid supplier for fitting. Headband Hearing AidsAs the name implies headband hearing aids have the whole aid mounted on a band over the head. Often the microphone, battery and amplifier are housed on one side while the bone vibrator is on the other. These aids have the advantage of being worn in an inconspicuous manner but lack the higher output available from body worn aids.All ages can wear headband bone conduction hearing aids as the headbands can be made to fit any size. One of the major problems is keeping the headband on the head. This can be helped by covering the band with textured fabric which will not slip on the hair, or tying tape around the back of the neck onto each side of the band. Bone Anchored Hearing AidsA method of fitting a titanium screw into the mastoid process making it possible to mount a vibrator on to it has been developed in Sweden. This makes a good system for transmitting sound into the head involving no pressure.Back to Top The Bone Anchored Hearing AidHeadaches and soreness of the skin caused by the pressure from the vibrator against the skull are common problems along with keeping the headband on the head and in the correct position. )
The Bone Anchored Hearing Aid uses the principle of osseointegration (bonding with the bone) to overcome these problems by attaching the aid to a small titanium screw which is implanted behind the ear. Surgical procedure and treatmentThe surgery is normally carried out in two stages and can be done under either local or general anaesthetic. Both operations are minor and take between 45 minutes and 1 hour to perform.Stage OneDuring this operation a small titanium screw 3-4 mm long is implanted into the bone directly behind the ear. This screw is called an implant or fixture. The side chosen for the implant is usually the side with the best bone conduction but this is discussed with the doctor before the operation as there may be other considerations to be taken into account.Stage Two) After 3-4 months the implant will have securely bonded with the bone. The second operation will now be carried out during which a titanium sleeve or abutment is
connected to the implant through the skin. It is this which provides the direct
connection between the hearing aid and the implant.
(Note: for adults in some cases the two stages may be combined into one procedure.)
What Happens Next?The site of the surgery has to be dressed and cleaned in the outpatients clinic on a regular basis for at least two weeks after the second operation.
Approximately one month later the hearing aid can be fitted. (In the case of a one-stage surgical procedure there will be a slightly longer time between the surgery and the fitting of the hearing aid.)
Routine audiological tests follow after a few weeks and then regular check-ups take place initially after 4-6 months and then every 6-12 months. Back to Top |
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