A cochlear implant is an electronic device that provides sound perception to patients with severe to profound sensorineural (nerve) hearing loss in both ears. The principle benefits of a cochlear implant are:
- aid in lipreading
- perception of environmental sounds
- aid in monitoring one's own voice.
In some patients, the implant may also allow understanding of speech without lipreading. Common to all cochlear implants is a bundle of fine wires, the electrode array, that is surgically implanted into the hearing portion of the inner ear -the cochlea. The external device includes the sound processor, a cable and a microphone that is housed in a head piece. The sound processor analyzes incoming sounds and converts those sounds into patterns of electrical current. The current is carried along the cable and delivered to the electrode array by radio wave transmission to an antenna and receiver implanted under the skin with the electrodes. The current from the electrode array then stimulates the fibers of the auditory nerve with the electric current and produces the perception of sound. The sound processor is individually programmed to best meet the needs of each patient.
Who benefits from a cochlear implant?
Cochlear implants can help patients with severe to profound sensorineural hearing loss in both ears who cannot benefit adequately from the use of hearing aids. Normally, when sound vibrations enter the ear canal, they are collected by the ear drum, conducted through the middle ear by three small bones (ossicles), and converted to pressure waves in the fluid of the cochlea (the snail shaped structure of the inner ear). These pressure waves travel through the inner ear fluid, bending the fibers at the top of the hair cells that convert the pressure waves to electrical signals. These signals are then carried by the auditory nerve to the brain.
Sensorineural hearing loss is defined as any abnormality of the inner ear that prevents the conversion of the pressure waves to electrical signals on the auditory nerve. In many cases of sensorineural hearing loss, the problem is due to hair cell damage. However, a significant number of auditory nerve fibers are still functional. Since the cochlear implant sends an electrical signal that stimulates the nerve fibers, directly bypassing the inner ear, these patients may perceive sound with the implant despite the damage in the inner ear.
FAQs - Frequently Asked Questions
Can every patient with severe to profound sensorineural hearing loss benefit from a cochlear implant?
Unfortunately, not everyone can benefit from using a cochlear implant. Some forms of sensorineural hearing loss destroy the auditory nerve fibers. Therefore, there is nothing for the cochlear implant to stimulate. In other forms of hearing loss, structural damage to the inner ear prevents surgical implantation. In many forms of sensorineural deafness, the status of the auditory nerve fibers is unknown. In such cases, it can be difficult to predict the potential benefit of receiving a cochlear implant. Currently, researchers are studying the relationship between then cause of deafness and the survival of auditory nerve fibers, to better predict performance before implantation. The duration of hearing loss and the age at which it occurred also seem to influence performance with an implant.
How do I know if I am a candidate?
Candidacy for cochlear implantation is determined by a team of specialists including an otologist (ear doctor), an audiologist, and a social worker. The otologist will obtain a complete history, perform a thorough exam, and order appropriate testing. The audiologist will evaluate your hearing by performing an audiogram (hearing test) and will also determine the appropriateness of amplification use. A review board will then evaluate this information to determine whether you are a cochlear implant candidate.
What is involved in having a cochlear implant operation?
Cochlear implantation surgery is performed under general anesthesia and takes approximately three hours. An incision is made behind the ear and, operating with the aid of a microscope, the surgeon drills away a portion of the mastoid bone (hard bone behind the ear) to gain access to the inner ear. A small opening is created into the cochlea. The electrode array is threaded into the cochlea and its outer end is attached to the bone of the skull. The incision is closed and the head bandaged. Most patients go home the next morning. Patients return the following week for suture removal.
When can I begin using the implant?
The patient returns at approximately one month following surgery to begin the use of the sound processor. The processor "hook-up" and programming is performed by the audiologist.
Initially, there are a series of visits to the audiologist to test and adjust the signal levels for the electrodes in the array. These settings can be updated at each visit over a period of weeks or months as the patient becomes more comfortable with experiencing sound again. Different kinds of listening tests are used to evaluate and develop the patient's ability to use the implant. With time, the patient will become accustomed to the cochlear implant. At first, sounds may be quite different than remembered prior to the hearing loss. Environmental sounds are usually the first to be identified or relearned.
Are there any alternatives to a cochlear implant?
Currently, cochlear implantation is limited to patients who cannot benefit significantly from using conventional hearing aids. Use of some combination of lipreading, cued speech, sign language, and powerful hearing aids are the only alternatives to implant surgery. An audiologist can direct you to sources for counseling and assistance that emphasize these alternatives.
What are the benefits of the cochlear implant?
The improvement in auditory perception (hearing) following cochlear implantation varies widely from patient to patient. Nearly all patients have some perception of sound. Even if this awareness is only the detection of the presence or absence of a sound in the environment, it can be a substantial aid to lipreading. In most cases, implantees have some additional ability to discriminate pitch and loudness, which further enhances the benefit of the device. In a limited number of patients, the implant may even provide good enough hearing to permit use of the telephone.
What are the risks of cochlear implantation?
Risks associated with cochlear implantation include those associated with the surgery itself, such as bleeding, infection, problems with anesthesia or healing, dizziness, or injury to the facial nerve. In addition, there are risks associated with the implant, such as mechanical or electrical failure, rejection, infection and problems that would require removal or replacement of the implant. Your surgeon will discuss all of these risks with you. Any/all of the ability to hear present in the operative ear prior to surgery surgery will be completely lost at time of implant surgery.