Cochlear Implant

What is a cochlear implant ?
A cochlear implant is an electronic device that can restore useful hearing and provide improved communication abilities for persons who have severe to profound sensorineural hearing loss (nerve deafness) and who cannot benefit from hearing aids.

How is an implant different from a hearing aid ?
Cochlear implants differ from hearing aids in two important ways:

1. Hearing aids simply amplify sounds. A cochlear implant, on the other hand, transforms speech and other sounds into electrical energy that is used to stimulate the hearing nerve in the inner ear.

2. Unlike most hearing aids, cochlear implants have both internal and external components. The implant system consists of an external speech processor and headset (worn behind the ear) and an internal, surgically implanted receiver/stimulator package with an electrode array.

How does the cochlear implant work ?
For people who are cochlear implant candidates, the outer ear and the middle ear function normally. However, in the inner ear (cochlea), the tiny hair cells are damaged or missing and do not generate electrical pulses to be sent to the hearing centres of the brain. Therefore, the brain does not perceive the sound.

The cochlear implant attempts to replace the function of the hair cells with electrical stimulation. Sounds are picked up by the microphone of the speech processor. The speech processor analyses and codes sounds into electrical pulses. These pulses are sent to the surgically implanted receiver/stimulator package and through to the electrode array, which stimulates the residual nerve fibres in the cochlea. The hearing nerve then sends these electrical pulses to the brain and which are finally interpreted as sound.

Who can benefit from Cochlear Implants ?
Any adult or child with bilateral (both ears) severe to profound sensorineural (nerve) hearing loss who obtains little or no benefit from hearing aids would be considered a candidate for a cochlear implant. Such deafness may be acquired following infection (such as meningitis), toxic effect of ototoxic drugs, trauma or age associated hearing loss.

Some children may be born with deafness. Such congenital hearing impairment is not uncommon with 1 to 2 out of every 1000 live births are born with significant hearing loss. Such children need to be identified at the earliest. This ensures that appropriate measures are undertaken to rehabilitate their hearing loss at a time when language skills can most easily be acquired. Many of these children may eventually require a cochlear implant.

Before the Cochlear Implant Surgery
Patients who are candidates for cochlear implantation would meet with the cochlear implant team comprising the surgeon, audiologist and hearing therapist for a detailed evaluation. This evaluation consists of a various hearing tests, speech and language assessment, hearing aid evaluation and medical examination. Some children may need to be seen by a Developmental Paediatrician to ensure that they can make the best use of their implant. CT and MRI scanning of the ears and routine blood tests for anaesthesia are also performed. Eventually the team will decide if a cochlear implant is the best option for the candidate.

Prior to surgery, patients are also seen by a physician or paediatrician (in the cases of children) to ensure they are fit for general anaesthesia. All candidates need to get vaccinations to reduce the risk of infections.

Cochlear Implant Surgery
Cochlear implant surgery lasts about two to three hours and is performed while the patient is under general anesthesia. The electrode array is inserted into the cochlea. The receiver/stimulator is secured to the skull. At the end of the operation the implant is tested by attaching it to the processor and making sure that it is functioning well. An x-ray is also obtained to ensure that the electrode array is positioned correctly.

Typically, patients remain in the hospital for two nights. They have a bandage on their head which is removed after a few days. Patients return to school or work as soon as they feel well enough to do so, usually within a week of surgery.

Switching on the implant
Activation of the implant takes place three to four weeks after implantation, allowing enough time for the incision to heal properly. The headset and speech processor is attached to the implant on the patient. The processor is then connected to a special computer by which the implant is 'programmed' or 'mapped'. Mapping is done on a regular basis during postoperative rehabilitation to fine-tune the processor and get the best performance as the patient gets used to hearing with the implant.

Postoperative Rehabilitation
Rehabilitation is an essential part for those who have undergone Cochlear Implantation and may be carried out at the hospital or at a centre close to the patient's home. All patients need Auditory Verbal Therapy (AVT). In Auditory Verbal Therapy, the emphasis is laid on making the child listen and speak normally, rather than on lip reading and visual cues. Learning to listen takes time and requires concerted efforts from the patient, the family and the person providing habilitation services. Thus the implant can offer a wide range of benefits, including hearing speech, environmental sounds and music.