Cochlear Implants

Definition

The cochlear implant is an electronic device that restores partial hearing to the deaf.

Description

The ear is divided into three parts: external ear, middle ear, and inner ear.

Sound travels along the ear canal of the external ear and causes the ear drum to vibrate. The three small bones of the middle ear conduct this vibration from the ear drum to the cochlea or auditory chamber of the inner ear. Fluid waves in the cochlea, initiated by movement of the three small ear bones, stimulate the more than sixteen thousand delicate hearing cells (hair cells). Movement of these hair cells generates an electrical current in the auditory nerve. This current is transmitted through various complicated interconnections in the brain stem to that portion of the brain that recognizes these electrical stimulations as sound.

When there is disease or obstruction in the external or middle ear, a conductive hearing impairment results. This impairment may be due to a variety of problems and may be corrected by medical or surgical treatment.

When the hearing impairment is due to a problem in the inner ear, a sensorineural impairment (nerve deafness) results. In most cases of sensorineural hearing loss, the hair cells have been damaged and do not function. Although many of the auditory nerve fibers may be intact and capable of transmitting electrical impulses to the brain, without functioning hair cells the nerve fibers remain unstimulated. Sensorineural hearing loss cannot be corrected medically.

How Cochlear Implants Work

Part of a cochlear implant is surgically implanted in the ear (temporal bone) and part is worn externally like a hearing aid. However, a cochlear implant is not a hearing aid in the sense of making sound louder or clearer. It is a medical device that bypasses damaged parts of the inner ear and electronically stimulates the nerve of hearing.

Cochlear implants are designed to bypass the hair cells that are not functioning and provide stimulation directly to the auditory nerve.

There are a number of different cochlear implants currently available. All systems consist of a microphone, a signal processor, a signal coupler (transmitter and receiver), and one or more electrodes that are implanted in or around the cochlea.

The microphone and signal processor are worn outside the body, like a hearing aid. Either a transmitter outside the body with a receiver inside, or a connector that protrudes through the skin just behind the ear, can be used. Both provide a direct connection between the signal processor and electrodes.

The electrical stimuli are sent inside the body to the implanted electrodes. The electrical signals stimulate the auditory nerve fibers, and the signal is then sent to the brain.

The cochlear implant is designed only for individuals who receive little benefit from hearing aids. Candidates are usually two years of age or older.

Cochlear Implant Surgery

Cochlear implant surgery is performed under general anesthesia. An incision is made behind the ear. The mastoid bone is opened, leading to the middle ear.

The operation takes several hours depending on the specific cochlear implant used. The hospital stay varies from one night to several days.

Benefits of the Cochlear Implant

Cochlear implants do not provide normal hearing. The majority of totally deaf patients who receive a cochlear implant are able to detect medium-to-loud sounds, including speech at comfortable listening levels. Many patients can learn to recognize some familiar sounds.

For many patients, cochlear implants aid in communication by improving lip-reading ability. They are able to use clues from the sounds and rhythms of speech and combine these with what they see.

Results vary for different individuals, depending on factors such as age at time of deafness, age at implant surgery, duration of deafness, status of the remaining auditory nerve fibers, and training.

Questions to Ask Your Doctor

How effective is a hearing aid?

Would the hearing improve with a cochlear implant?

What type of candidate would benefit from an implant?

How would the procedure be performed?

How long is the hospital stay?

What are the possible risks and complications?

What can be expected with respect to improvement in hearing?