Surgery

Cochlear Implants Explained



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A cochlear implant can enable a profoundly deaf person to gain a representation of sounds and to understand speech. If implanted early, a young deaf child can learn to understand speech well enough to speak normally and develop normal language skills.

The cochlear is a spiral shaped organ in the inner ear. In a person with normal hearing, vibration waves from the ear drum and other components of the inner ear are transformed into fluid waves in the cochlear, and these are in turn transformed into nerve impulses that pass along the cochlear nerve to the brain. The cochlear implant bypasses the hearing components that are not working, or barely working.

The implant does not make the recipient hear as hearing people do, and is not like a hearing aid, which amplifies sounds to help out people with damaged hearing, since a hearing aid requires the ears to be working at least to some extent. Instead, the implant completely bypasses the damaged parts of the inner ear and directly stimulates the cochlear nerve, and this is interpreted as sounds by the brain, even by a person with no hearing at all.

The cochlear implant is a small electronic device consisting of two sections: and external section fixed behind the ear, and an internal section implanted inside the ear. The external components are a microphone to pick up sounds, a transmitter, and a sound processor that interprets the sounds. These processed sound signals are then passed to the internal components: a transmitter that transmits the sounds to a receiver/stimulator, which converts them to electrical impulses. These are in turn passed to a group of electrodes, which use the signals to stimulate the auditory nerve. The brain interprets the inputs from the nerve in much the same way as if the signals had originated from well-functioning ears. The sounds are not exactly the same as heard sounds, and it does take some time to learn to understand the inputs, but once mastered, the cochlear implant allows the deaf person to carry on normal conversations without reliance on lip-reading or other visual cues.

Candidates for implantation are tested to determine the damage to their hearing and whether or not an implantation would be of benefit. Tests include a physical examination, a psychological assessment, and they may include an MRI or a CT scan, especially if the patient has had meningitis, since this can affect the shape of the cochlear and interfere with an implant.

Implantation of the cochlear device is done through surgery under a general anaesthetic, and is followed up by intensive therapy to learn how to interpret the signals supplied to the brain. Normally, only one implant is inserted, but some patients have two, or have a hearing aid in one ear and an implant in the other.

The surgery consists of an incision in the skin above and behind the ear, after the area is shaved and cleaned. The skin is then pulled apart and held in place by clamps, and a layer of the skull bone is removed by a device resembling a dental drill that scrapes away the bone. The internal components are then inserted into the inner ear behind the ear drum, and the skin incision is then closed up.

After the operation, the patient may feel some discomfort at first, and may also have the usual complications after anaesthesia, such as nausea, confusion, and a sore throat from the breathing tube used during the operation. In most cases the patient can go home the day after surgery, and will return a week later to have the stitches removed. The external components are fitted behind the ear about three to six weeks after the operation, when the area has had time to heal, and the swelling has gone down. At this time the implant is turned on, and training begins. Until this time the implant has no effect on the hearing.

Generally, a family member will also take part in the training, especially if the patient is a child, and will learn how to manage the sound processor to ensure the implant is working optimally.

Research into improving cochlear implants is continuing, but they are already enabling adults who have lost their hearing to regain it, and they enable profoundly deaf children to experience the world of sound and to develop language skills. There are even reports that for children with a cochlear implant, vocal quality and intelligibility of speech are better than for hearing children.

For more information, refer to the FDA website.

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