What is a Cochlear Implant?
A Cochlear implant (CI) is a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf or severely hard of hearing. The cochlear implant is often referred to as a bionic ear. Unlike hearing aids, the cochlear implant does not amplify sound. Instead, it works by directly stimulating any functioning auditory nerves inside the cochlea with electrical impulses.
External components of the cochlear implant include a microphone, speech processor and transmitter. The transmitter allows an individual to adjust the sound for quality and amplification.
How Many People Have an Implant?
According to researchers at the University of Michigan, approximately 100,000 people worldwide have received cochlear implants. Recipients are split almost evenly between children and adults. The vast majority are in developed countries due to the high cost of the device, surgery and post-implantation therapy. Mexico had performed only 55 cochlear implant operations by the year 2000 (Berruecos 2000).
China will be having 15,000 cochlear implant surgeries on children, which are being paid for by a Taiwanese philanthropist. There is concern that the follow-up services in China are not adequate to meet the needs of cochlear implanted children. A small percentage of those now have bilateral implants, or one on each cochlea. Bilateral cochlear implants are a growing trend globally, Cochlear Americas reported that 15% of their 2006 sales in the United States were for bilateral implants.
Individuals who have acquired deafblindness (loss of hearing and vision combined) may find cochlear implants a radical improvement in their daily life. It may provide them with more information for safety, communication, balance, orientation, and mobility and promote interaction within their environment and with other people, reducing isolation. Having more auditory information that they may be familiar with may provide them an independent gathering of information to become more independent.
The implant often gives recipients additional auditory information, which may include sound discrimination fine enough to understand speech in quiet environments. Though sufficient, and quality, post-implantation rehabilitative therapy is a critical factor affecting the success rate.
The introduction of cochlear implants has seen the renewal of a century-old debate about models of deafness that often pits hearing parents of deaf children against the Deaf community. There is a debate about whether Cochlear implants are ethically sound; see Ethics below.
Parts of the Cochlear Implant
The implant is surgically placed under the skin behind the ear. The basic parts of the device include: External
- a microphone which picks up sound from the environment
- a speech processor which selectively filters sound. It prioritizes audible speech and sends the electrical sound signals through a thin cable to the transmitter,
- a transmitter, which is a coil held in position by a magnet placed behind the external ear. It transmits the processed sound signals to the internal device by electromagnetic induction,
- a receiver and stimulator secured in the bone beneath the skin, which converts the signals into electric impulses and sends them through an internal cable to electrodes,
- an array of up to 22 electrodes wound through the cochlea, which sends the impulses to the nerves in the scala tympani and then directly to the brain through the auditory nerve system.
Candidates for Cochlear Implants
There are a number of factors that determine the degree of success to expect from the operation and the device itself. Cochlear implant centers determine implant candidacy on an individual basis and take into account a person’s hearing history, cause of hearing loss, amount of residual hearing, speech recognition ability, health status, and family commitment to aural habilitation/rehabilitation.
A prime candidate for a cochlear implant is described as:
- Having severe to profound sensorineural hearing impairment in both ears
- having a functioning auditory nerve
- having lived a short amount of time without hearing (approximately 70+ decibel loss, on average)
- having good speech, language, and communication skills, or in the case of infants and young children, having a family willing to work toward speech and language skills with therapy
- not benefiting enough from other kinds of hearing aids
- having no medical reason to avoid surgery
- living in or desiring to live in the “hearing world”
- having realistic expectations about results
- having the support of family and friends
- having appropriate services set up for post-cochlear implant aural rehabilitation (through a speech-language pathologist, deaf educator, or auditory verbal therapist).
Type of hearing impairment
People with mild or moderate sensorineural hearing loss are generally not candidates for cochlear implantation. After the implant is put into place, sound no longer travels via the ear canal and middle ear but will be picked up by a microphone and sent through the device’s speech processor to the implant’s electrodes inside the cochlea. Thus, most candidates have been diagnosed with profound sensorineural hearing loss.
The presence of auditory nerve fibers is essential to the functioning of the device: if these are damaged to such an extent that they cannot receive electrical stimuli, the implant will not work. A small number of individuals with severe auditory neuropathy may also benefit from cochlear implants.
Age of Cochlear Implant Recipient
Post-lingually deaf adults and pre-lingually deaf children form two distinct groups of potential users of cochlear implants with different needs and outcomes. Those who have lost their hearing as adults were the first group to find cochlear implants useful, in regaining some comprehension of speech and other sounds.
If an individual has been deaf for a long period of time, the brain may begin using the area of the brain used for hearing for other functions. If such a person receives a cochlear implant, the sounds can be very disorienting, and the brain often will struggle to adapt to sound. The risk of surgery in older patients must be weighed against the improvement in the quality of life. As the devices improve, particularly the sound processor hardware and software, the benefit is often judged to be worth the surgical risk, particularly for the newly deaf elderly patient.
The other group of customers is parents of children born deaf who want to ensure that their children grow up with good spoken language skills. Research shows that congenitally deaf children who receive cochlear implants at a young age (less than 2 years) have better success with them than congenitally deaf children who first receive the implants at a later age, though the critical period for utilizing auditory information does not close completely until adolescence.
Cost of Cochlear Implants
In the United States, medical costs run from USD$45,000 to $105,000; this includes evaluation, the surgery itself, hardware (device), hospitalization and rehabilitation. Some or all of this may be covered by health insurance. In the United Kingdom, the NHS covers cochlear implants in full, as does Medicare in Australia. According to the US National Institute on Deafness and Other Communication Disorders, the estimated total cost is $60,000 per person implanted.
Cochlear Implant Risks
Some effects of implantation are irreversible; while the device promises to provide new sound information for a recipient, the implantation process inevitably results in damage to nerve cells within the cochlea, which often results in a permanent loss of most residual natural hearing.
While recent improvements in implant technology, and implantation techniques, promise to minimize such damage, the risk and extent of the damage still vary. In addition, while the device can help the recipient better hear and understand sounds in their environment, it is simply incapable of replicating the quality of sound processed by a natural cochlea.
As a result, some recipients can only distinguish the difference between simple sounds, such as a ringing phone vs a doorbell, while others can clearly understand speech in quiet environments, while some even gain the ability to distinguish the nuances of fine classical music. The success rate depends on a variety of factors, including technology used, condition of the recipient’s cochlea, and the follow-through of post-implantation aural rehabilitation. The FDA reports that cochlear implant recipients may be at higher risk for meningitis.
 A study of 4,265 American children who received implants between 1997 and 2002 concluded that recipient children had a risk of pneumococcal meningitis more than 30 times greater than that for children in the general population.
 A later, UK-based, study found that while the incidence of meningitis in implanted adults was significantly higher than the general population, the incidence in children was no different than the general population.
 There are strict protocols in choosing candidates to avoid risks and disadvantages. A battery of tests is performed to make the decision of candidacy easier. For example, some patients suffer from deafness medial to the cochlea – typically acoustic neuromas. Implantation into the cochlea has a low success rate with these people as the artificial signal does not have a healthy nerve to travel along.
With careful selection of candidates, the risks of implantation are minimized.
Cochlear Implant Manufacturers
Currently (as of 2007), the three cochlear implant devices approved for use in the U.S. are manufactured by Cochlear Limited, Australia, MED-EL, Austria and Advanced Bionics, US. In the EU, an additional device manufactured by Neurelec, of France is available.
Each manufacturer has adapted some of the successful innovations of the other companies to their own devices. There is no clear-cut consensus that any one of these implants is superior to the others. Users of all four devices display a wide range of performance after implantation.
Since the devices have a similar range of outcomes, other criteria are often considered when choosing a cochlear implant: usability of external components, cosmetic factors, battery life, reliability of the internal and external components, MRI compatibility, mapping strategies, customer service from the manufacturer, the familiarity of the user’s surgeon and audiologist with the particular device, and anatomical concerns.
Cochlear America’s Australian Stock Exchange filings in August 2007 reported a record profit of A$100 million (or just over US$85 million) and a 70% market share. Cochlear’s 2007 annual report acknowledges that a Federal investigation continues into its payments to physicians and providers. In February 2007, part of the whistleblower complaint against Cochlear filed by former Chief Financial Officer Brenda March was unsealed by the U.S. District Court for the District of Colorado.
The complaint alleges that Cochlear violated the Federal anti-kickback statute through its Partners Program, which offered credits towards free or discounted products for physicians who implanted Cochlear devices, as well as gifts, trips, and other gratuities paid to physicians and providers. The government intervened in the case and transferred it from the U.S. Department of Justice to the Health and Human Services Inspector General for the imposition of civil penalties. The number of sanctions is not yet known.
All text is available under the terms of the GNU Free Documentation License.
Read the Wikipedia article on Cochlear Implants.