Cochlear implants can be adjusted to user's hearing needs
Dr. Eve Glazier and Dr. Elizabeth Ko
Tuesday, January 23, 2018
Dear Doctor: I'm contemplating a cochlear implant for my right ear. How do they work, and what is the success rate of such procedures?
Dear Reader: Unlike a hearing aid, which is a mechanical apparatus that amplifies sound, a cochlear implant is a medical device that delivers electrical stimuli directly to the auditory nerve. Hearing aids can be helpful in cases of mild to moderate hearing loss. But for individuals whose hearing loss is severe or profound, a cochlear implant can help.
That said, it's important to understand that a cochlear implant can't offer the same hearing experience as the human ear. And to understand why, we first need to talk a bit about how the ear works. (Are any of our regular readers surprised?)
When we hear a sound, it's because a complex series of functions have taken place. It begins as vibrations traveling through the outer, middle and inner ear. On each phase of that journey, a series of remarkable structures transform those vibrations until they reach the brain and are interpreted as the countless sounds — and noises — of the world around us.
Let's say it's raining. The vibrations from droplets striking various surfaces are "collected" by the funnel of the outer ear and an inner auditory canal. At the end of this canal sits the eardrum, which connects to a trio of tiny bones. These pick up and amplify the vibrations, and transmit them to the snail-shaped cochlea in the inner ear. Within the cochlea, a fluid begins to ripple. When tiny hair-shaped sensory cells touch a membrane, chemicals that create an electrical signal are released. This signal travels along the auditory nerve to the brain, which presents us with the sound of rainfall.
With a cochlear implant, which is made up of two parts, vibrations bypass the hair cells of the inner ear. Instead, the speech processor, worn behind the ear like a hearing aid, sends the information directly to a receiver-stimulator, a small device that is surgically placed beneath the skin. Electrodes from the receiver connect via the cochlea to the auditory nerve. When the processor picks up sound, the receiver turns it into electrical impulses and sends them to the brain. But because the hair cells within the cochlea, which give us the countless nuances of sound, are not involved, the hearing experience is not the same.
How well someone does with a cochlear implant depends in part on what degree of hearing they began with. Learning to interpret the impulses sent by the implant takes practice and can be challenging. Like hearing aids, there are several varieties of implants, and all can be adjusted to best fit the user's needs.
Risks include nerve injury, infection, meningitis, numbness around the ear, vertigo, tinnitus and the risks associated with anesthesia during the initial operation. Some implants fail and must be removed. For people with implants, scans like an MRI may not be possible.
Today, well over 60,000 adults in the United States use implants. If you do move forward, we suggest getting in touch with an organization that offers assistance to people who are deaf and hard of hearing. Also, going to a support group for cochlear-implanted patients can be a good way to get firsthand feedback.
Eve Glazier, M.D., MBA, is an internist and assistant professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and primary care physician at UCLA Health.