What is a cochlear implant?
Webpage published: 2012
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%.
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.
Image: Thanks to Cochlear Europe.
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.
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.
Webcast of a live bilateral operation on a 3 year old boy in Cleveland, Ohio, USA. Full running commentary both by the surgeon and an audiologist with explanatory slide presentations.
Thanks to the National Cochlear Implant Users Association (NCIUA) for their help in creating this, and to Cochlear Europe for supplying images.