A cochlear implant is an electronic device that enables people who are deaf or have profound hearing loss to perceive and process sounds.
Hearing loss can make it difficult or even impossible for people to perform daily tasks like using a telephone, listening to the radio, or having conversations with friends and family. Because people who are very hard-of-hearing may not be able to hear fire alarms or traffic sounds or doorbells, it can affect personal safety and autonomy. Hearing loss can also affect employment. Children with hearing loss may have difficulties learning to speak or understanding speech; adults may find employment opportunities limited.
For people with significant hearing loss, cochlear implants can be life-changing. Not only can the device help people detect sounds they couldn’t hear before, it can also improve quality of life.
“Hearing loss can be extremely disabling,” says Yale Medicine ear, nose, and throat specialist and skull-base surgeon Douglas Hildrew, MD. “Our ability to hear helps us shape and interact with the world around us. Severe hearing loss can therefore cause isolation, social withdrawal, loneliness, and even early-onset confusion.”
“Cochlear implants are a life-changing technology that provides the ability to restore one of the most important senses for patients for whom all other technologies have failed,” says Yale Medicine head and neck surgeon Nofrat Schwartz, MD. Dr. Hildrew agrees. “They are truly amazing and have advanced considerably over the years,” he says. “One of the most amazing parts of my job is to have a patient describe what it’s like to hear the birds again, and a family member tell me their loved one is ‘back.’ It seems nothing short of a miracle.”
What is a cochlear implant?
A cochlear implant is made up of external and internal components. The external part is held in place, behind the ear, with a magnet. The internal component is surgically implanted in the ear, under the skin.
Cochlear implants are not the same as hearing aids. Whereas a hearing aid amplifies sound to help people hear better, a cochlear implant takes in sounds from the outside world and transmits them electrically to the auditory nerve. The signals are then sent to the brain, which transforms them into sounds.
Although cochlear implants can enable people with severe or profound hearing loss to perceive sounds, they cannot deliver “traditional” hearing. Part of the process involves engaging in aural rehabilitation, which helps train the brain to interpret the sounds it receives from the device. Recipients can detect and recognize sounds, and most are able to understand speech and have conversations with others.
How do cochlear implants work?
For people who hear normally, sound waves from the outside environment enter the ear and are directed along the ear canal to the eardrum. The sound waves cause the eardrum to vibrate, which in turn, makes the bones of the middle ear vibrate as well. The vibrations then reach the cochlea, a snail-shaped part of the inner ear, where they cause special cells (called hair cells) to move and bend. The hair cells produce electrical signals that are transmitted to the auditory nerve and then to the brain.
Hearing loss and deafness are often caused by damage to the hair cells in the cochlea. Diseases, congenital (present at birth) abnormalities, genetic disposition, and exposure to noise can damage them, impairing their ability to send signals to the auditory nerve, resulting in hearing loss.
Cochlear implants help people with this type of hearing loss by bypassing the damaged hair cells. As noted above, cochlear implants have two main components:
- The external component consists of a microphone, a sound processor, and a transmitter. The microphone receives sound waves from the surrounding environment. The sound processor converts them into electrical signals, which the transmitter sends to the internal part of the cochlear implant.
- The internal component consists of a receiver/stimulator and a thin wire called an electrode array which is inserted in the cochlea. The electrical signals from the transmitter go to the receiver and are then transmitted along the wire to the auditory nerve, stimulating it to send signals to the brain.
Each of these two components contains a magnet as well. They hold the external component in place, just over the implanted receiver/stimulator component. The external part of the device can be removed easily for bathing or swimming.
Who can receive a cochlear implant?
Cochlear implants may be an option for children and adults who are deaf or who have significant hearing loss.
To determine whether a cochlear implant may be helpful to a particular person, ear, nose, and throat (ENT) doctors start by running several tests. These may include hearing tests to evaluate a patient’s degree of hearing loss and ability to recognize speech, a general physical exam, a psychological evaluation, and imaging tests such as a computed tomography (CT) or magnetic resonance imaging (MRI) scan of the ear and brain.
Patients must be prepared to participate in an aural (hearing) rehabilitation program. It’s also important that they have realistic expectations about the degree of hearing improvement cochlear implants can provide.
In general, criteria for cochlear implantation include:
- Age of 12 months or over
- Severe to profound hearing loss in both ears (although there has been recent approval for use in single-sided deafness in some cases)
- Hearing not adequately improved using a hearing aid
- No pre-existing conditions that rule out cochlear implants
What happens during cochlear implant surgery?
The surgery is an outpatient procedure that takes about two hours.
At the start of cochlear implant surgery, patients are given general anesthesia, so they won’t be awake or feel pain during the procedure.
The surgeon begins by making an incision in the skin behind the ear, then makes a small hole in the mastoid bone (the bone behind the ear) to gain access to the middle ear. The next step is to “open the round window” or to create an opening of the cochlea.
Next, the surgeon inserts the receiver/stimulator part of the cochlear implant under the skin behind the ear. Once the receiver/stimulator is in place, the electrode array—essentially a thin wire—is inserted into the cochlea, allowing hearing preservation, if possible. The surgeon then closes the incision to complete the procedure.
What happens after cochlear implant surgery?
Most people are able to go home the same day of the surgery, though sometimes, an overnight hospital stay is required. Patients may be given pain medication after the procedure and will be instructed about how to best care for the surgical wound as it heals.
People who get cochlear implants will not be able to perceive sounds from the ear with the implant until the external part of the device is activated. This is done after the patient has healed from the procedure, typically one to four weeks after surgery.
To activate the device, the external part of the cochlear implant is fitted behind the recipient’s ear. An audiologist then programs the implant’s sound processor, adjusting loudness and other settings to enhance speech and sound recognition. In most cases, the settings need to be fine-tuned over several appointments to optimize sound quality.
Initially, many implant recipients report that voices sound mechanical. Usually, the sound quality improves over time, in particular, during the first three to six months after activating the sound processor.
Participation in aural rehabilitation is an important part of recovery. There, implant recipients work with audiologists and speech-language pathologists to learn how to better perceive speech and other sounds. Speech therapy is especially important in helping toddlers with cochlear implants learn to speak.
What are the risks of cochlear implant surgery?
While cochlear implant surgery is a safe procedure, like all surgeries, it comes with some risks. These may include:
- Infection of the surgical wound
- Taste disturbances
- Tinnitus (ringing in ears)
- Vertigo and/or dizziness
- Numbness around ear
- Facial nerve stimulation (twitching of eye, lip, or another part of the face)
Very rare complications include:
- Facial nerve damage (resulting in temporary or permanent weakness or paralysis of one side of the face)
- Failure of the device (e.g., mechanical or electrical failure or damage, improper placement)
- Migration of cochlear implant (the implant moves from the site where it was initially implanted, for instance due to physical trauma)
- Cerebrospinal fluid (CSF) leak (CSF surrounds the brain and spinal cord)
What is the outlook for people who receive cochlear implants?
Outcomes for people who receive cochlear implants can vary. Many implant recipients are able to understand speech, use the telephone, and “be part of the hearing world,” says Dr. Schwartz.
Children with hearing loss often have difficulties learning to talk, which can affect their education, future employment, and earning prospects. Cochlear implants can help hard-of-hearing and deaf children learn to talk and understand speech, enabling them to attend mainstream classes.
What makes Yale Medicine unique in its approach to cochlear implants?
“At Yale, we provide a multidisciplinary approach to hearing rehabilitation and cochlear implantation,” says Dr. Schwartz. “We employ the most advanced surgical techniques for hearing preservation to afford the best outcome. The surgeons and audiologists work hand-in-hand to provide the most comprehensive, patient-tailored treatment for hearing rehabilitation.”