Cochlear implants
A cochlear implant is a surgically implanted electronic device that provides a sense of sound to a person who has a severe or profound hearing loss. A cochlear implant does not cure deafness or hearing impairment, but is a prosthetic substitute which directly stimulates the cochlea. There are over 250,000 users world wide; 12,000 in the UK.
The expectations of how well a cochlear implant will help someone hear have to be addressed prior to implantation, as although the device can help the person hear better and detect environmental sounds, it is not as good as the quality of sound processed by a natural cochlea and therefore will not restore hearing to normal levels.
However it can be a significant improvement for the person in comparison to any previously tried hearing aids. Generally speaking if the person being implanted has lost their hearing after they have learnt language, cochlear implants can be a great help, in particular for people who have recently lost their hearing.
Although the improvements in implantation techniques are ongoing there are still risks attached to surgery and a possibility that the surgery will fail and will not restore hearing. Having said that, cochlear implants are the world's most successful medical prostheses in that less than 0.2% of recipients reject it or do not use it and the failure rate needing reimplantation is around 0.5%.
Who may be suitable for a cochlear implant?
To reduce the risks of implantation there are strict protocols in place to help chose the right candidate, these factors cover issues around the operation and the device. A battery of tests and questionnaires cover the person’s hearing history, cause of hearing loss, amount of residual hearing, speech recognition ability, health status, and family commitment to aural habilitation/rehabilitation.
A prime candidate is described as:
- having severe to profound sensorineural hearing impairment in both ears with a functioning auditory nerve
- good speech, language, and communication skills
- showing little benefit from the latest model of high powered hearing aids
- having no medical reason to avoid surgery
- living in or desiring to live in the "hearing world"
- realistic expectations aboutresults
- support of family and friends
How does it work?
A cochlear implant completely by-passes the defunct normal hearing mechanism and stimulates the auditory nerve directly by means of an internally implanted electrode assembly.
The sound processor (A) captures sound and turns it into digital code. The sound processor has a battery that powers the entire system.
The sound processor transmits the digitally-coded sound through the coil (B) to the implant (C) just under the skin.
The implant (D) converts the digitally-coded sound into electrical signals and sends them along the electrode array which is positioned in the cochlea (the inner ear) (D).
The implant's electrodes stimulate the cochlea's hearing nerve fibres (E), which relay the sound signals to the brain to produce hearing sensations.
All cochlear implant systems have the same broad characteristics and design principles and are all well engineered. Variations arise in styling, accessories and battery type. Particular differences exist in electrode design and speech processing strategies which encode the external sound frequency details into digital signals.
Surgery
During the operation the surgeon makes an incision behind the ear being treated in order to gain access into the middle ear and cochlea. The surrounding area behind the ear will be shaved to facilitate this and this will quickly regrow. The operation lasts about three hours and typically people spend one night in hospital.
The operation is delicate and intricate rather than dangerous because no vital organs are disturbed. There are no serious attendant risks with this operation beyond those normally associated with major surgery. People are requested not to wash their hair for three weeks during this healing process but there are no other restrictions on normal activities.
Switch on
Up to six weeks after the operation, the person will return to the implant centre for ‘Switch On’. Here the audiologist will fit the external speech processor and connect it to the computer used to adjust the settings on the device. When switched on, the speech processor sends signals to the electrodes in the cochlea for the first time. The audiologist will spend time 'tuning' it to help the person start to 'hear'.
Once the speech processor's microphone is activated, the first thing people hear is the audiologist asking if they can hear! Conversation may sound quite different from what is remembered. It is often described as mechanical or tinny. But these effects quickly disappear and speech becomes more natural-sounding as a person adjusts and gains more exposure to the sounds of conversation.
After 'Switch On' people need some weeks to get used to hearing with the implant and there will be several tuning sessions with the audiologist.
In parallel, there will be ‘hearing lessons’ from a Speech and Language Therapist who will help the person identify different sounds and distinguish vowels and consonants during a series of lessons. There are conversation exercises to do at home with friends and family. The extent of this important training will depend on the nature of the hearing loss and the extent to which the implant is performing.
Adults with a long duration of deafness prior to implantation may take longer to achieve the full benefits and will, generally, need more support from the rehabilitation team. Recently deafened adults generally adapt faster to the use of their implant.
More information
Further information can be seen at the following links:
Please follow these links to the cochlear implant companies' own websites:
- Advanced Bionics manufacturer of the Harmony cochlear implant.
- Cochlear manufacturer of the Nucleus cochlear implant.
- MED-EL manufacturer of the Maestro cochlear implant.
- Neurelec manufacturer of the Digisonic cochlear implant.
Thanks to the National Cochlear Implant Users Association (NCIUA) for their help in creating this page, and to Cochlear Europe for supplying images.