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to Home PageThe cochlear implant is an elective treatment for those who have lost all or most of their useful hearing in both ears. Figures collected by the MRC Institute of Hearing Research show that at the end of the year 2000, more than 1,500 adults and more than 1,400 children had received implants in the UK.
Sound waves coming into the ear canal cause changes in the air pressure which makes the tympanic membrane, or ear drum vibrate. These vibrations in turn move the three little bones called the malleus, incus & stapes (sometimes known as the hammer, anvil & stirrup) in the middle ear, and the stapes hammers against the membrane, or skin, covering the oval window, the entrance to the cochlea (inner ear). This bony structure is shaped like a snail shell.
Inside the hollow cochlea there are fluid filled canals divided by a membrane. On the membrane there are thousands of hair cells which are connected to the cochlear (or auditory) nerve.
The pressure on the oval window from the vibration of the sound waves causes the fluid in the canals to move. This stimulates the hair cells and they generate minute electrical impulses that pass along the cochlear nerve to the brain. The hair cells near the entrance of the cochlea are sensitive to high sounds and those towards the apex, or highest point, of the cochlea respond to low sounds. The electrical signals are interpreted by the brain as sound; environmental noises, music and speech.
When there is a very severe to total sensorineural hearing loss it is usually because the hair cells in the cochlea are so damaged that they do not create these electrical signals, or enough of them, to make use of a hearing aid satisfactory. The cochlear nerve is usually intact. The cochlear implant is so named because it is implanted in the cochlea.
A cochlear implant is an electronic device. A small part of it is surgically implanted in the cochlea to provide direct electrical stimulation of the cochlear nerve. It gives a sensation of hearing. There is also an externally worn part. This is a speech processor that is connected to a headpiece with a microphone to pick up the sound waves. The processor converts them into minute electrical signals. The headpiece has a transmitter, which sends the electrical signals through the skin to the receiver and internal implant. The transmitter is held in place over the internally implanted receiver above the pinna, or outer ear, by a magnet.
A wire leads down from the receiver into the middle ear and then into the cochlea itself. The implant has eight or more electrodes depending on which device is used. The electrodes are placed at intervals along the part of the wire, which is called the electrode array. This is threaded into the cochlea. The electrical signals from the processor are sent to the electrodes. Like the hair cells in the normal ear, the electrodes at the beginning of the electrode array are usually stimulated by the high frequencies and those at the end of the array, near the apex of the cochlea, by the low frequencies. The signals then pass along the cochlear nerve and are decoded in the auditory centre of the brain and the implant user "hears".
Some implant centres offer a choice of device. Click here for a list of implant centres in the UK. There are three main implant manufacturers. Visit the manufacturers' websites for details of the types of device currently available.
Some cochlear implant users hear very well indeed. They can even use a telephone quite normally and go about their daily life reasonably well. Not everyone is so successful, but users who do not gain as much can still hear environmental sounds like dogs barking, birds singing and the doorbell. Best of all, most people find conversation easier and more relaxed because their hearing helps them to lip-read better even if they cannot understand speech through hearing alone.
Cochlear implants are suitable for adults and children who have a severe to profound sensorineural deafness in both ears, and cannot gain significant benefits from conventional hearing aids. Young children have special requirements, especially with regard to the assessment, selection and follow-up procedures. Click here for more details about implants for children.
Implants are suitable for adults who have become profoundly or very severely deaf. An adult who was born profoundly deaf, or became profoundly deaf in the first few years of life, will probably not benefit substantially from a cochlear implant. However an adult born partially deaf who then had a progressive loss might benefit more because they have some memory of sound. Cochlear implants are suitable both for those who have been deaf for years and for those who have become deaf recently.
Adults who have been deaf for a long time take longer to get full benefit from their implant - there are more cobwebs to brush away. Newly deafened users quite often hear and recognise environmental sounds and speech almost as soon as the implant is switched on. Age is not a barrier to implantation and some successful users are now in their eighties and even nineties.
Older children can benefit from cochlear implants in the same way as adults provided they have become deaf after acquiring speech and language or have been born hearing impaired and are good hearing aid users, Sometimes a cochlear implant is better than a hearing aid for a severely deaf person.
For further information on how to get an implant, its benefits, the operation and treatment involved and on future research and development in the implant field, please click here.
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