Treating Hearing Loss: How Do Cochlear Implants Work & Who Should Consider Them?Oct. 13, 2021 - Katie McCallum
About one in eight Americans aged 12 and older have some level of hearing loss in both ears.
Unfortunately, many forms of hearing loss are irreversible and worsen with age. But that doesn't mean a person can't do anything about it. Indeed, it's estimated that 28.8 million Americans could benefit from using hearing aids.
For those with disabling hearing loss, though, hearing aids may not be enough.
While rare in younger people, disabling hearing loss becomes much more common with increasing age, occurring in:
- 2% of 45 to 55-year-olds
- 9% of 55 to 65-year-olds
- 25% of 65 to 74-year-olds
- 50% of those who are 75 and older
And, if hearing aids aren't helping, there's another hearing loss treatment option for a person to consider: cochlear implants.
"A cochlear implant is an implantable device that uses a wire electrode placed inside the cochlea to convert normal acoustic sound into electric signals that directly stimulate the nerve of hearing, called the cochlear nerve," says Dr. Kenny Lin, an ENT doctor specializing in ear health (otology) at Houston Methodist. "They're used to help restore hearing in those with severe to profound sensorineural hearing loss."
Sensorineural hearing loss is loss caused by damage to the inner ear or the nerve from the ear to the brain.
Dr. Lin compares cochlear implants to cardiac pacemakers, another implantable device that uses electrical signals through an electrode. In that case, the electrical signals pace the heart at a regular rhythm.
For those considering cochlear implants, Dr. Lin is here to answer common questions you may have, including how these implants work and who is eligible for them.
What is a cochlear implant?
A cochlear implant is a small but sophisticated electronic device with two primary components:
- An external sound processor, which includes a microphone, speech processor and transmitter
- An internal receiver/stimulator
"The first component is the external sound processor. Sound is picked up by a microphone, encoded into an electronic signal by the speech processor and then transmitted to the second component, the implant itself," explains Dr. Lin. "The receiver/stimulator, which is surgically implanted under the skin behind the ear, sends this information to an electrode placed within your cochlea and stimulates the cochlear nerve."
The external and internal components magnetically attach through the skin, and power is transferred to the receiver/stimulator through the magnet, similar to wireless charging for newer smartphones and smartwatches.
How does a cochlear implant work?
The external sound processor plays a huge role in helping restore hearing, but most of the "magic" of a cochlear implant happens inside your ear — within your cochlea.
"Our ability to distinguish pitch of sound is spatially arranged along the cochlear nerve, such that high pitches (like a flute or whistle) are at one end of the nerve and low pitches (like a drum or trumpet) are at the other end," says Dr. Lin. "A cochlear implant takes advantage of this."
The electrode array that's implanted within the cochlea contains 16 to 22 electrodes that are positioned along the cochlear nerve. This allows the electrode to deliver sound information by selectively stimulating different parts of the nerve.
The cochlear nerve then sends this information to the brain, which interprets these electrical signals as sound.
What does a cochlear implant sound like?
After cochlear implant surgery, a person doesn't wake up with perfect hearing. That's because it can take the brain up to six months to fully learn how to use the new sound information it's receiving from the implant.
"The initial sound quality is often described as 'robotic' or 'tinny' — like Darth Vader or Micky Mouse — but the brain quickly learns to match the sounds you are hearing to what it should normally sound like," says Dr. Lin. "This process continues over the first few months and your performance will steadily improve."
What happens during cochlear implant surgery?
Through a single incision made behind the ear lobe, the surgeon places the implant under the soft tissue just above the bone of the skull located behind and above the ear.
The electrode is then placed inside the cochlea. Using a microscope and drill system, a pathway is made through the mastoid bone behind the ear into the middle ear, where the opening of the cochlea, called the round window, is identified. The electrode is then carefully threaded through the round window and into the cochlea.
"Cochlear implant surgery was developed in the 1980s and has become a very common and standardized procedure," says Dr. Lin. "The risks are minimal. I think a lot of people are also surprised to learn that it's an outpatient surgery that takes less than two hours of operating time, so there's no overnight hospital stay or lengthy recovery."
The implant site is allowed to heal for two weeks before an audiologist activates it. And, again, there's then a learning curve for the brain as it adjusts to hearing in this new way.
"Prior to the surgery, a person typically has 0%-20% word understanding in the affected ear," says Dr. Lin. "After implantation, the average implant user will achieve 60%-70% word understanding using the device alone after just six months of use."
Cochlear implant vs. hearing aid: Which do you need?
"Cochlear implants aren't for everyone," says Dr. Lin. "For instance, people with only mild to moderate hearing loss who primarily have trouble keeping up with conversation in noisy environments might get all that they need from hearing aids."
But for others, hearing loss may be much more significant. And when hearing aids are no longer helping enough, the inability to communicate clearly leads to frequent misunderstandings and frustration.
The two main groups of patients who benefit from cochlear implants are:
- Young children born with hearing loss
- Adults who lose their hearing over time
"Traditionally, the candidacy criteria in adults was severe to profound deafness in both ears with tested word understanding less than 50% and limited benefit from the use of hearing aids," says Dr. Lin. "More recently, however, the candidacy criteria has expanded to include people with profound hearing loss in one ear (single-sided deafness), as well as certain people with less severe forms of hearing loss."
In those with single-sided deafness, Dr. Lin says the primary benefits of a cochlear implant are improvements in hearing in situations with background noise, improved ability to identify where sounds are coming from and a reduction in ringing in the ears (tinnitus).
"If you're concerned about your hearing or the hearing of someone you love, the best place to start is to consult with an audiologist and an otolaryngologist specializing in hearing health," recommends Dr. Lin. "These are hearing experts who will perform a hearing test, explain your current level of hearing loss and counsel you on your options for hearing rehabilitation — whether hearing aids or more advanced technology such as cochlear implants."