Aids and Implants - some questions answered
1)
Can a hearing aid be fitted to any person who is deaf irrespective of the
degree and cause of deafness?
The general answer is yes. Except in the very profoundly deaf person, any person who is deaf can benefit from a hearing aid. However in conductive deafness the improvement maybe much better compared to sensory neural deafness. This is because of the element of distortion of speech which is seen in people with sensory neural deafness, is not seen in conductive deafness. This also explains why these people tend to hear better when they are in a quiet environment, and when spoken to in a slow clear voice, rather than being shouted at.
2) What is the basic principle of a hearing aid?
A hearing aid is basically an amplifier of sound and consists of a microphone, amplifier, receiver, ear mould and battery. Depending on how these items are organized, and their respective sizes hearing aids can be categorized into different types. Some of these also have advanced electronics to refine the end result of the sound delivered to the user.
3) What are the different types of hearing aids
available?
There are several types of hearing aids available in the market which can be summarized as below.
Body-worn aids - These have a relatively large unit containing the microphone, batteries and amplifier. This unit is worn on the chest, in the pocket, or in a harness. A long wire carries the amplified signal to the receiver which is fitted to the ear mould. These aids are powerful, and maintenance is cheap as they use average AA size batteries. They have large control knobs and switches making it user friendly to a feeble person. This is the type of aid usually issued to profoundly deaf children. The disadvantage is that they are large, do not localize sound well and can cause distortion of the sound by the rubbing of cloths on the aid.
Behind the ear aid (BE aid) - This is a much smaller unit which contains all the parts housed together. It is worn behind the ear, and the sound from the receiver is carried through a short plastic tube to the ear mould. These aids also are quite powerful and have the advantage of good localization of sound as the microphone is placed at ear level. They are also better accepted by the deaf person. In children they are less prone to accidental damage. The disadvantage is in the higher incidence of feedback, the cost of the batteries and the initial cost of the aid which is much more than a body-worn type.
In the ear aid - These aids are much smaller, and takes the appearance of an ear mould which is placed in the ear. The controls are very small, and so is the battery. Feedback is again a problem, and they are expensive. However they are much less obvious when worn.
Completely in the canal aid (CIC aid) - These are very small aids which fit into the ear canal completely. They are quite expensive and have similar problems to the other small aids, but once worn are virtually invisible. One additional problem is that they may get lost very easily due to the small size!
4)
What is feedback and why is an ear-mould needed?
Any person who has seen someone taking a BE hearing aid out of the ear, would have noticed that it makes a whistling noise, until it is switched off. This is due to the fact that the sound coming from the receiver, re-enters the microphone causing it to be re-amplified, resulting in feedback. This can happen while the aid is being used, if the sound escapes from the ear to re-enter the microphone. Thus the need for a close fitting ear mould. The ear mould is made on a cast obtained from the patients ear. This is done in a hearing aid lab. If a aid is used without a mould, but using only the ear piece supplied by the manufacturer, this problem can arise.
5) Are there any special problems or difficulties related to the use of a hearing aid?
One problem is when there is a chronic ear infection, with a constant discharge. The other group is when there are abnormalities of the pinna or ear canal, which makes it impossible to fix the hearing aid. In both these groups a bone conductor aid can be used.
6) What is a
bone conductor aid?
A bone conductor aid delivers the amplified sound directly to the skull, by passing the middle ear, to reach the cochlear. The receiver powers a vibrator placed on the mastoid bone. In children this can be kept in place using a head band, and in adults it can be incorporated to a pair of spectacle frames.
7) Can a
person who is profoundly deaf on one side only be helped?
Yes, a CROS aid can be used. CROS stands for Contralateral Routing of Signal. This is to facilitate hearing in a person with a completely deaf ear on one side, which will not benefit with a hearing aid. The sounds from the deaf side are picked up, and amplified, and are directed to the better ear for the person to hear them. This can be done using wires and a spectacle frame. More modern methods use radio signals to send the sound to the better ear, without the need for wires.
8) What is
the procedure followed in fitting hearing aids?
The first thing to do is to diagnose the cause for the deafness, and treat it if possible. This itself may cure the deafness. Impacted wax, glue ear, foreign bodies or anatomical blocks such as osteomata of the ear canal are a few such cases. If there is no such cause the child or adult should undergo audiological evaluation to assess the level and type of deafness. These results should be analyzed to exclude other possible causes such as acoustic neuromata which will need to be tackled without delay. Once the diagnosis is clearly a deafness with no treatable cause a hearing aid can be advised.
9) Does one
need special training to use a hearing aid?
For a post lingually deaf adult no special training is needed except the initial acclimatization to the new aid. However in the case of a child, and specially in a pre lingually deaf child a prolonged period of speech therapy is necessary to get the maximum benefit from the aid.
10) Who is a pre lingually deaf child?
A child develops speech during the first five years of life. If a child is born deaf, or becomes profoundly deaf before the age of five years, then the development of speech will not occur, and the child becomes pre lingually deaf. This type of person is difficult to rehabilitate compared to a post lingually deaf person, who has become deaf after acquiring proper speech. Also the older the pre lingually deaf person, the more difficult to acquire speech. This is because the tonotopic pattern of the cochlea seems to get established on the cerebral hemisphere(usually left), during the early years of life. Thus it is important to get a child to hear as soon as possible, if speech is to be established properly.
11) Is a hearing aid the only device available to help a deaf person to
communicate?
No. While the hearing aid is the foundation on which the rehabilitation of the deaf is based on, there are quite a number of other appliances and methods available to help the deaf. The following are a few of them.
Radio aids The major drawback of a hearing aid is that they amplify not only what the person wants to hear, but also the surrounding background sounds. This could be a problem in noisy surroundings, and specially in a class room situations. The radio aid consists of a transmitter which transmits the teachers voice as radio waves, and a receiver worn by the child to hear the transmission. This allows the child to hear only what is talked into the transmitter and no other background noise. The receiver may be incorporated to the normal hearing aid, or be worn separately.
Electro magnetic induction loop This consists of a wire loop which is placed around a room or hall. The person talking to the deaf person speaks to a microphone connected to an amplifier. This in turn sets a magnetic field inside the room, which can be picked up by the hearing aid. For this to happen the control switch on the aid must be placed to the ‘T’ setting. This type of loop is widely used in public buildings, railway stations, post offices and in public telephone booths. It may also be used at home or schools.
Lip reading Lip-reading is a skill which has to be developed. The less one hears, the more one has to rely on lip reading. But the better one hears, easier to develop the skill of lip reading. This is because a lot of words may look similar when spoken, and some clue from the sound will help to differentiate them. thus lip reading and hearing aids are complementary to each other. It is important to talk to a deaf child in a normal way, without artificial stress on any word, for the child to acquire the rules of the language. This will help immensely in learning the art of lip reading.
Sign language Sign language is not a specific language like English shown with signs. It is a group of languages with their own rules, structure and ways of expression. It involves not only the hands and arms but the whole person with body movements and eye contact. A single sign may express more than one word. There are different types of sign languages. The British Sign Language is one such example.
12) Is there such a thing called a Bionic Ear?
This is a name given to the cochlear implant, which was a breakthrough in the management of deafness, and which is now gradually gaining momentum. A cochlear implant is basically an electronic device, which is capable of stimulating the cochlear nerve directly, thereby by-passing the cochlear hair cell transducer system. In other words it replaces the cochlear, which normally converts sound energy to electrical energy, which in turn stimulates the cochlear nerve.
13) When is a cochlear implant indicated?
A cochlear implant is indicated in people who are profoundly deaf, and cannot be helped with even the most powerful hearing aid. It can be implanted in adults or children.
14) What is the principle behind the cochlear implant?
The cochlear implant works on the principle that, even in the most severely deaf person, there remains some neuronal elements capable of being stimulated. An exception to this is in certain types of congenitally abnormal inner ears where there may be no neuronal elements present. This is also true of obliterative labyrinthitis, such as post meningitic, where the cochlear may not be patent.
15) What are the components of the cochlear implant?
16)
Does a cochlear implant replace a hearing aid?
No, a cochlear implant is only indicated in the profoundly deaf people, who cannot be helped by a hearing aid. The hearing aid gives a much better quality of hearing when compared to a cochlear implant.
17) Are there different types of cochlear
implants
Yes, the earlier version of implants had only one electrode, and were called single channel implants which was placed close to the cochlear. The new implants have multiple electrodes and are called multichannel cochlear implants. The latter are more frequency sensitive and give a better speech perception and production. However they are placed inside the cochlear, and involves a more complicated surgical procedure. They are also more expensive.
18) Is the cochlear implant the ultimate method of making a person hear?
No, the bionic ear has been taken a step further with the Auditory Brainstem Implant., and the hearing aid has been taken further as the Implantable Hearing Device.
The Auditory Brainstem Implant The limitation of the cochlear implant is that, it depends on an intact cochlear nerve for it to function. Thus, for a large number of persons with bilateral auditory nerve degeneration, or who have undergone surgical resection of the cochlear nerve, such as in the excision of bilateral acoustic neuromata, the cochlear implant will not work. In this type of situation it is now possible to stimulate the cochlear nuclear complex in the brain stem directly. This is done by the surgical placement of an electrode , on the cochlear nuclear complex, and stimulating it in a similar way to the cochlear implant. This has been achieved successfully in a very limited number of cases, and needs further refinements in the design and placement of the electrodes to make it more efficient and accurate.
Implantable Hearing Devices The main limitation of the standard hearing aid is that it uses the external auditory canal to transmit the sound. Therefore in persons where the external ear canal cannot be used, it may be impossible to use the standard hearing aid. These are people with congenitally abnormal ears, narrow ear canals, chronically infected ears and ears which have surgical defects. In these cases a bone conducting aid can be used, but it the results can be much improved by the use of an implanted hearing device.
There are 2 basic types of such devices. The first may use an implanted screw on the skull behind the ear, to which a bone conducting aid is screwed on. The screw is made of Titanium, and has achieved osseointergration after being implanted, and will remain as a percutaneous screw on a permanent basis (BAHA or Bone Anchored Hearing Aid).
It may also take the form an implanted rare earth magnet(e.g. neodymium- iron-boron magnet, laser welded onto a titanium-aluminium-vitallium container, which in turn is attached to a Herbert orthopaedic screw) which is screwed on to the skull under the post aural skin, This is made to vibrate by an electromagnetic coil placed on top of it, on the surface of the skin. Thus it is a transcutaneous device as opposed to the percutaneous screw.
The second type is much more interesting in that, it uses an implanted hearing device which receives electrical sound signals from an external amplifier, which in turn are converted back into vibrations, which are transmitted to the ossicular chain, making the person hear through the normal air conduction pathway. In other words the sound a person should hear is first converted to electrical signals like in a regular hearing aid, but instead of feeding it as sound to the ear canal through a receiver, it vibrates an implanted device attached to the ossicular chain. An example is the Partially Implantable Hearing Device, or the artificial middle ear, which has been used in ears following tympanomastoid surgery.
Conclusion
It has been attempted to highlight some important aspects ,of the different methods available to the deaf person to help him, or her to lead a normal life as much as possible. The mainstay in the management of the deaf is the hearing aid, but it must be appreciated that other techniques such as lip reading, sign language and other electronic devices also play a major role. Hearing aids have their limitations, and to overcome these major scientific discoveries, like the cochlear implant, and the implantable hearing device have been made. There is much more scope by way of more advanced techniques, such as the auditory brain stem implant, and possibly even more, by an increased awareness of these methods, and their proper application to suit the individual deaf person.