How Cochlear Implants Improve Hearing and Change Lives

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 also known as a bionic ear. Unlike hearing aids, the cochlear implant does not simply amplify sound. Instead, it directly stimulates any functioning auditory nerves inside the cochlea with electrical impulses.

External components of the cochlear implant include the following:

• microphone
• speech processor
• 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, more than 400,000 people worldwide have received cochlear implants. Recipients are split almost evenly between children and adults. The vast majority live 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 2000 (Berruecos 2000).

In China, children receive many cochlear implant surgeries, which, in some cases. There is concern that the follow-up services in China are inadequate to meet the needs of cochlear-implanted children. Some 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 lives. The hearing device may give them more information for safety, communication, balance, orientation, and mobility. Additionally, it may help promote interaction within their environment and with other people, reducing isolation. Having more auditory information they may be familiar with may help them become more independent.

The implant often gives recipients additional auditory information. For example, this may include sound discrimination acceptable enough to understand speech in quiet environments. However, sufficient and quality, post-implantation rehabilitative therapy is critical to the success rate.

The introduction of cochlear implants reactivated the century-old debate about models of deafness. These debates often pit 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 essential parts of the device include:

External:

• A microphone that picks up sound from the environment
• A speech processor that selectively filters sound. It prioritizes audible speech and sends the electrical sound signals through a thin cable to the transmitter
• transmitter, a coil held in position by a magnet behind the external ear. It transmits the processed sound signals to the internal device by electromagnetic induction,

Internal:

• A receiver and stimulator secured in the bone beneath the skin convert the signals into electric impulses and send them through an internal cable to electrodes,
• An array of up to 22 electrodes wound through the cochlea. The electrodes send the impulses to the nerves in the scala tympani and then directly to the brain through the auditory nerve system.

Candidates for Cochlear Implants

Many factors determine the degree of success to expect from the operation and the device itself. Cochlear implant centers determine implant candidacy on an individual basis. They consider a person’s hearing history, cause of hearing loss, amount of residual hearing, speech recognition ability, and health status. In addition, they consider the family’s commitment to aural habilitation/rehabilitation.

A prime candidate for a cochlear implant is someone:

• 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. 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 a surgeon places the implant, sound no longer travels via the ear canal and middle ear. Instead, a microphone picks up sound and sends it 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 device’s functioning. If these are damaged to the extent that they cannot receive electrical stimuli, the implant will not work. Some 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 from 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 functional. They found that it helped them regain some comprehension of speech and other sounds.

If an individual has been deaf for an extended period, the brain may begin using the area of the brain used for hearing for other functions. The sounds can be very disorienting if someone receives a cochlear implant. As a result, the brain often struggles to adapt to sound.

Older patients must weigh the risk of surgery against improving their quality of life. As the devices improve, particularly the sound processor hardware and software, the benefit is often considered worth the surgical risk. This is particularly true for the newly deaf elderly patient.

The other potential customers are 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 two years) have better success than congenitally deaf children who first receive the implants at a later age. However, 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 $45,000 to $105,000. This includes evaluation, surgery, 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. This is the same for 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 damages nerve cells within the cochlea. This 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, the device can help the recipient better hear and understand sounds in their environment. However, it is 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 the technology used, the 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.

[1] 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.

[2] A later, UK-based, study found that while the incidence of meningitis in implanted adults was significantly higher than in the general population, the incidence in children was no different than in the general population.

[3] 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 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, the U.S. District Court for the District of Colorado unsealed part of the whistleblower complaint against Cochlear filed by former Chief Financial Officer Brenda March.

The complaint alleges Cochlear violated the Federal anti-kickback statute through its Partners Program. For example, the program allegedly offered credits towards free or discounted products for physicians who implanted Cochlear devices and 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.

For more information, learn about the history of the implantable hearing device. Also, check out these hearing resources.