A cochlear implant is a medical device to improve hearing. It helps people who have a significant
hearing loss and who cannot benefit from regular hearing aids. A cochlear implant has two parts:
Implant, which is placed into the inner ear during surgery, and a Sound processor which is worn behind the ear like a hearing aid:
- The sound processor picks up and filters sounds.
- The sound processor translates the filtered sounds into digital information and sends it to the internal implant.
- The internal implant converts the digital information into electrical signals, and sends them to a tiny, delicate curl of electrodes that sits gently inside the cochlea.
- The electrical signals from the electrodes stimulate the hearing nerve, bypassing the damaged cells that cause hearing loss, allowing the brain to ‘hear’ sound.
The cochlear implant is very different from the traditional hearing aid in several ways:
- Traditional hearing aids help people hear by making sounds louder similar to increasing the volume on the television. The cochlear implant on the other hand helps people hear by electrically stimulating the hearing nerve.
- The cochlear implant has an internal component that requires surgery. A hearing aid does not.
- The cochlear implant does not sound like normal hearing or even hearing with a hearing aid. It takes time and practice for the sound to improve.
- Hearing aids can help people who have different types and degrees of hearing loss. Cochlear implants are only for those with moderate-profound sensorineural hearing loss in both ears who do not benefit from hearing aids.
Both children and adults may be candidates for a cochlear implant.
Adults must meet a minimum set of requirements:
- 18 years of age or older*
- Severe to profound sensorineural hearing loss in both ears
- Little or no speech understanding even with well fitted hearing aids
- Communicate primarily through spoken language
- Realistic expectations
- Strong motivation and commitment to be part of the hearing world
- No medical contra-indications
Children: (12 months to 17 years)
- 12 months or older
- Severe to profound sensorineural hearing loss
- Limited benefit from binaural amplification trial.
- No medical contra-indications
- Enrollment in appropriate educational program with emphasis on development of auditory/oral skills
- Family and/or child with good motivation and realistic expectations about the cochlear implant
Patients undergo surgery under general anesthetic. When the patient is asleep, the surgeon makes an incision behind the ear. S/He may shave a small amount of hair behind the ear before the incision. Also, the mastoid bone, a honeycomb of air cells behind the ear, is drilled (a mastoidectomy).
The surgery takes approximately 2 hours. Usually, patients leave the hospital in the company of a friend or family member the same day of the surgery. While cochlear implant surgery is a safe surgical procedure, there are always risks associated with surgery. Although current implants and surgical techniques are designed to try to preserve any natural hearing in the implanted ear, any natural hearing in the implanted ear may be gone after implant surgery. Other possible complications include dizziness, tinnitus, facial paralysis, a change in the sensation of taste and/or infection.
Following the surgery there is a 3- 6 week waiting period to allow the ear to heal. During this time, there is no hearing in the ear with the cochlear implant. At the activation appointment, the audiologist programs (maps) the cochlear implant, works with the recipient to learn to use the sound of the cochlear implant (listening practice), reviews the sound processor and the accessories provided with the cochlear implant, performs baseline assessments of implant functioning and measures speech understanding. There will be several mapping appointments in the first year and annual follow up appointments after that.
If appropriate, the recipient may wear a hearing aid in the opposite ear to the implant. Typically, people with bimodal (cochlear implant in one ear and hearing aid in the other ear) do better than people who hear with the cochlear implant alone.
Several factors affect how people hear and understand with the cochlear implant. These include the age at which the hearing loss occurred, the age at implantation, how the person heard with hearing aids, the status of the cochlea, and any other disabilities or diagnoses (cognitive disabilities/dementia, etc.) Both children and adults need (re )habilitation after the implant. It takes time and practice to develop good listening skills with the cochlear implant.
More recently, the development of other types of implants help those individuals with other types or amounts of hearing loss.
Hybrid Implants:
Hybrid implants and sound processors offer both electrical (cochlear implant) and acoustic (hearing aid) stimulation (EAS) in the same ear. Candidates for these implants have relatively good hearing in the low frequencies and more severe to profound hearing loss in the high frequencies. Candidacy criteria differ slightly than for cochlear implants.
Bone Anchored Hearing Aids (BAHA):
BAHA devices consist of an implantable device and an external sound processor. The sound processor sends the sound to the implant. Vibrations from the implant transmit sound through bone conduction to the inner ear. As with cochlear implants, BAHA devices are a medical device with Health Canada approval.
This category of implantable devices may be appropriate for adults and children (5 years and older) who:
- Have conductive or mixed (conductive and sensorineural) hearing loss and/or
- with chronic external or middle ear problems or
- are born with ear malformations.