Copyright © 1990 American Academy of Otolaryngology - Head and Neck Surgery, Inc. This leaflet is published as a public service. The material may be freely used for noncommercial purposes so long as attribution is given to the American Academy of Otolaryngology - Head and Neck Surgery, Inc., One Prince Street, Alexandria, VA 22314-3357.
Worldwide, approximately one person in a thousand is born deaf. Almost an equal number of people born with hearing will develop deafness during their lifetime. Approximately 250,000 to 500,000 people in the United States could benefit from a cochlear implant.
The cochlear implant is an electronic device which restores partial hearing to the totally deaf. 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 which bypasses damaged parts of the inner ear and electronically stimulates the nerve of hearing.
Normal Hearing
The ear is divided into three parts: external ear, middle ear, and inner ear. Each part performs an important function in the process of hearing. 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 (malleus, incus, and stapes) 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.
Types of Hearing Impairment
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. Senorineural hearing loss cannot be corrected medically.
How Cochlear Implants Work
Cochlear implants are designed to bypass the hair cells which are not functioning and provide stimulation directly to the auditory nerve. There are a number of different cochlear implants currently available. All cochlear implant 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 may 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.
Becoming a Cochlear Implant Patient
The cochlear implant is designed only for individuals who receive little benefit from hearing aids. Candidates are usually two years of age or older. Becoming a cochlear implant patient involves an evaluation, including otologic, audiologic, radiographic and psychological tests.
Ear (Otologic) Evaluation
An examination must be performed to assure there is no active infection or other problem within the middle or inner ear that would preclude the surgical placement of the implant.
Hearing (Audiologic) Evaluation Extensive hearing tests must be performed to determine the degree of hearing with and without a hearing aid. Special tests are performed to evaluate benefits from hearing aids.
X-Ray (Radiographic) Evaluation
Special x-rays, usually computerized tomography (CT) scans, are taken to evaluate the condition of the inner ear bone.
Psychological Evaluation
Psychological evaluation is required for some cochlear implant programs.
Physical Examination
A general physical examination is performed to identify possible problems with general anesthesia or surgical implantation of the electrode assembly.
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 from 1.5 to 5 hours depending on the specific cochlear implant being used. The hospital stay varies from one night to several days, depending on the device used and the patient's needs.
How a Cochlear Implant Produces Hearing:
Postoperative Care, Training & Follow-Up
The patient returns to the implant clinic one to two months following surgery and is fitted with the external portions of the device (signal processor, microphone, transmitter). Instruction in the care and maintenance of the system and training in listening to sound through the implant are provided at that time. Cochlear implant programs differ in the amount of time required to fit the device and the amount of training provided. In addition, patients are usually required to continue returning to the clinic at regular intervals for check-up and assessment.
What to Expect from a 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. In a smaller number of patients, the implant provides some understanding (discrimination) of words or sentences without the use of lip-reading.
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, training, etc. The cochlear implant clinics explain reasonable expectations for each situation. It is important to clearly understand the time commitments before making a decision about the cochlear implant. There are a small number of patients for whom a cochlear implant is not beneficial.
Related Information
Cochlear implant surgery is performed by otolaryngologists (ear, nose, and throat specialists). However, not all otolaryngologists perform this procedure. Your local ear doctor should be able to refer you to a cochlear implant center.
Because cochlear implants are medical devices, they are regulated by the Food and Drug Administration (FDA). Each new device must undergo clinical investigation at a limited number of cochlear implant clinics before it is approved for general use. These clinical investigations, and the approval that may follow, are done separately for adults and children.
Whether a device is approved or still under investigation may make a difference as to who is a candidate to receive the implant, how frequently return visits to the clinic are required, and whether insurance companies will pay for the procedure. It will also make a difference in how much is known about the safety and benefits of a particular device.
Each manufacturer of cochlear implants has brochures and other patient information. Be sure to ask your cochlear implant doctor for written information. It is important to be fully informed regarding the benefits and the risks of cochlear implantation.
Costs
A cochlear implant is considerably more expensive than a hearing aid. Total costs (evaluation, surgery, device, rehabilitation) may range from about $15,000 to more than $25,000. If the cochlear implant device is approved by the FDA, many insurance companies will provide benefits that cover some or much of the cost.