A cochlear implant is an electronic device that restores partial hearing to individuals with severe to profound hearing loss who do not benefit from a conventional hearing aid. It is surgically implanted in the inner ear and activated by a device worn outside the ear. Unlike a hearing aid, it does not make sound louder or clearer. Instead, the device bypasses damaged parts of the auditory system and directly stimulates the nerve of hearing, allowing individuals who are profoundly hearing impaired to receive sound.
WHAT IS NORMAL HEARING?
Your ear consists of three parts that play a vital role in hearingthe external ear, middle ear, and inner ear. Conductive hearing: Sound travels along the ear canal of the external ear, causing the ear drum to vibrate. Three small bones of the middle ear conduct this vibration from the eardrum to the cochlea (auditory chamber) of the inner ear. Sensorineural hearing: When the three small bones move, they start waves of fluid in the cochlea, and these waves stimulate more than 16,000 delicate hearing cells (hair cells). As these hair cells move, they generate an electrical current in the auditory nerve. The electrical signal travels through inter-connections in the brain to specific areas of the brain that recognize it as sound.
How is hearing impaired? If you have disease or obstruction involving your ear canal, tympanic membrane (ear drum), or middle ear, your conductive hearing may be impaired. Medical or surgical treatment can probably correct this or a hearing aid can be used in certain instances. An inner ear problem, however, can result in a sensorineural impairment or nerve deafness. In most cases, the hair cells are damaged and do not function. Although many auditory nerve fibers may be intact and can transmit electrical impulses to the brain, these nerve fibers are unresponsive because of hair cell damage. Since severe sensorineural hearing loss cannot be corrected with medicine, it can be treated only with a cochlear implant.
HOW DO COCHLEAR IMPLANTS WORK?Cochlear implants bypass damaged hair cells and convert speech and environmental sounds into electrical signals and send these signals to the hearing nerve. A cochlear implant has two main components:
- An internal component that consists of a small electronic device that is surgically implanted under the skin behind the ear, connected to electrodes that are inserted inside the cochlea.
- An external component, usually worn behind the ear, that consists of a speech processor, microphone, and battery compartment.
The microphone captures sound, allowing the speech processor to translate it into distinctive electrical signals. These signals or "codes" are transmitted across the skin via radio waves to the internal electronic stimulator. The internal stimulator then sends the signals to the implanted electrodes in the cochlea. The electrodes signals stimulate the auditory nerve fibers to send information to the brain, where it is interpreted as meaningful sound.
COCHLEAR IMPLANT BENEFITSCochlear implants are designed only for individuals who attain almost no benefit from a hearing aid. They must be 12 months of age or older (unless childhood meningitis is responsible for deafness). Otolaryngologists (ear, nose, and throat specialists) perform implant surgery, although not all of them do this procedure. Your local doctor can refer you to an implant clinic for an evaluation. The implant team (otolaryngologist, audiologist, nurse, and others) will determine your candidacy for a cochlear implant and review what you may expect as a result of the cochlear implant. The implant team will also conduct a series of tests, including: Ear (otologic) evaluation: The otolaryngologist examines the ear canal and middle ear to ensure that no active infection or other abnormality precludes the implant surgery. Physical examination: Your otolaryngologist also performs a physical examination to identify any potential problems with the use of general anesthesia needed for the implant procedure. Hearing (audiologic) evaluation: The audiologist performs extensive hearing tests to find out how much you can hear with and without a hearing aid. X-ray (radiographic) evaluation: Special X-rays are taken, usually computerized tomography (CT) or magnetic resonance imaging (MRI) scans, to evaluate your inner ear anatomy.
COCHLEAR IMPLANT SURGERY
Cochlear implant surgery is usually performed as an outpatient procedure under general anesthesia. An incision is made behind the ear to open the mastoid bone leading to the middle ear space. Once the middle ear space is exposed, an opening is made in the cochlea and the implant electrodes are inserted. The electronic device at the base of the electrode array is then placed under the skin behind the ear.
IS THERE CARE AND TRAINING AFTER THE OPERATION?
Several weeks after surgery, your cochlear implant team places the signal processor, microphone, and implant transmitter outside your ear and adjusts them. They teach you how to look after the system and how to listen to sound through the implant. There are many causes of hearing loss and some patients may take longer to fit and require more training due to individual differences. Your team will ask you to come back to the clinic for regular checkups and readjustment of the speech processor as needed.
WHAT CAN I EXPECT FROM AN IMPLANT?
Most adult cochlear implant patients notice an immediate improvement in their communication skills. Children require time to benefit from their cochlear implant, as the brain needs to learn to correctly interpret the electrical sound input. While cochlear implants do not restore normal hearing, and benefits vary from one individual to another, most users find that cochlear implants help them communicate better through improved lip-reading. Also, 90 percent of adult cochlear implant patients are able to discriminate speech without the use of visual cues. There are many factors that contribute to the degree of benefit a user receives from a cochlear implant, including:
- How long a person has been deaf,
- The number of surviving auditory nerve fibers, and
- A patients motivation to learn to hear.
Your team will explain what you can reasonably expect. Before deciding whether your implant is working well, you need to understand clearly how much time you must commit. It is rare that patients do not benefit from a cochlear implant.
FDA APPROVAL FOR IMPLANTS
The Food and Drug Administration (FDA) regulates cochlear implant devices for both adults and children and approves them only after thorough clinical investigation. Be sure to ask your otolaryngologist for written information, including brochures provided by the implant manufacturers. You need to be fully informed about the benefits and risks of cochlear implants, including how much is known about safety, reliability, and effectiveness of a device; how often you must come back to the clinic for checkups; and whether your insurance company pays for the procedure.