Cochlear implant assessment service and electric-acoustic simulation

How does the ear work?

The ear is made up of 3 parts, the outer (external) ear, the middle ear and the inner ear.


  1. The part we can see is the outer ear which also includes the ear canal. It functions to capture sound energy and funnel it to the ear drum. When the sound energy reaches the ear drum, it causes the ear drum to move and vibrate.
  1. There are three tiny middle ear bones connected to the ear drum. When the ear drum vibrates, it causes the three bones to vibrate as well. 
  1. As these bones vibrate they push against the inner ear (cochlea). The cochlea is a fluid filled organ which contains many sensory cells called hair cells. As the 3 bones push against the cochlea the fluid inside the cochlea begins to move, which causes the hair cells to move and bend. The hair cells contact the nerve of hearing (auditory nerve) and as they move and bend they stimulate the nerve. The nerve then sends the message to the brain for processing.

In the case of severe to profound deafness, the hair cells and part of the hearing nerve are affected. This is called sensorineural hearing loss. This damage prevents the sound signals from being transmitted to the brain. 

More information about cochlear implants can be found on the National Deaf Children's Society website.

What is a cochlear implant?

A cochlear implant is an electronic device used to bypass an impaired inner ear.

People who have a bilateral (both ears) severe or profound sensorineural hearing loss (in the inner ear) and who are not able to hear speech optimally through conventional hearing aids may be referred for cochlear implant assessment.

What does a cochlear implant system look like?

It is made up of 2 parts:  

  • the internal implant
  • the external sound processor


Internal implant











External sound processor











How does a cochlear implant work?

  1. Sounds in the environment are picked up by the microphone, which sends the signal to the speech processor. 
  2. The speech processor filters the sound into coded signals. 
  3. The coded signals are then sent to the transmitting coil which sends the signal through the skin to the implanted receiver.
  4. The receiver electrically activates the electrode array which in turn stimulates the auditory nerve. 
  5. Nerve impulses are sent to the brain where they are interpreted as sound.

Patients with some residual low frequency hearing may be assessed for a combined electric acoustic cochlear implant.

What is electric acoustic simulation?

Electric acoustic simulation uses a cochlear implant and natural hearing together. The device can consist of a cochlear implant combined with a hearing aid. People who have more hearing in the low-mid pitches use the hearing aid for acoustic amplification and the cochlear implant for the stimulating the high pitches that they are not able to hear as well.

What brands of cochlear implant are available?

We offer 3 different brands of implants: Advanced bionics, Cochlear, and Med-el. We'll decide which brands will suit your child best and we'll try to offer you a choice.

If I receive a cochlear implant, will I be able to hear normally?

Children are entitled to 2 cochlear implants on the NHS. A cochlear implant does not restore normal hearing.

With a cochlear implant your child should be able to hear sounds that they were not able to hear with hearing aids. Although they'll be able to hear more sounds, they'll need to learn to use and understand these sounds. Receiving a cochlear implant is simply the first step in a very long process. The degree of success they'll have in developing listening skills cannot be predicted. However, with the proper training and support they'll have the best chance of being a successful implant user. 

What are the benefits of a cochlear implant?

Cochlear implants can provide access to a wide range of environmental sounds and the full spectrum of speech sounds. They do not restore normal hearing but can provide an opportunity to access spoken language and improve quality of life.

The outcomes for each implant recipient will vary and depend on many factors which include: duration of deafness, age at implantation, the presence of any anatomical abnormalities or additional difficulties and the support they receive.

The expected outcomes for your child will be discussed with you during the assessment.

What are the risks?

Cochlear implant surgery requires general anaesthetic:

Every operation carries risks and possible side effects. The chances of these occurring are very small and many only last a short time following surgery. These may include:

  • infection
  • bleeding
  • dizziness
  • nausea or vomiting
  • tinnitus (ringing in the ears)
  • weakness in facial muscles
  • taste disturbances
  • leak of cerebrospinal fluid (the fluid surrounding the brain)

Many of these are able to be monitored during surgery or treated immediately after.

There is also a small chance not all the electrodes of the implant can be inserted or that the device may fail and need removing or replacing.

Watch videos about cochlear implant surgery


Before cochlear implant surgery

During cochlear implant surgery

After cochlear implant surgery

Are there other alternatives?

You or your child could continue to wear hearing aids and make the most of limited access to speech with specialist teaching and support. Sign language could be used to support you or your child’s language skills.


Phone: 020 7188 6245
Fax: 020 7188 8905

Repairs and spares

Phone: 020 7188 6245

How to find us

Ear, nose and throat (ENT) services
2nd floor, Lambeth Wing
St Thomas’ Hospital
Westminster Bridge Road
London SE1 7EH

Map to ENT services at St Thomas'