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. Cochlear implants are often referred to as a bionic ear.

Cochlear implants can restore hearing in patients suffering deafness due to loss of sensory hair cells in their cochlea.

Candidates

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 is described as:

• having severe to profound sensorineural hearing impairment in both ears.
• having a functioning auditory nerve
• having lived at least a short amount of time without hearing (approximately 70+ decibel hearing 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 benefitting enough from other kinds of hearing aids, including latest models of high power hearing instruments and FM systems
• 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).

Age of recipient

Post-lingually deaf adults, pre-lingually deaf children and post-lingually impaired people (usually children) who have lost hearing due to diseases such as meningitis, form three 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 typically 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 readapt to sound.

The risk of surgery in the older patient must be weighed against the improvement in 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.

Another group of 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 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. Additionally, a 2010 study into bilateral implantation showed that children who receive their first cochlear implant before the age of 1½ responded well to the second one, even if the second one was implanted as late as 9 years old. In contrast, children who got their implants at age 2½ years or later did not respond as well to the later second implant, regardless of when they received it.One doctor has said "There is a time window during which they can get an implant and learn to speak. From the ages of two to four, that ability diminishes a little bit. And by age nine, there is zero chance that they will learn to speak properly. So it’s really important that they get recognized and evaluated early."

The third groups who will benefit substantially from cochlear implantation are post-lingual subjects who have lost hearing: a common cause is childhood meningitis. Young children (under five years) in these cases often make excellent progress after implantation because they have learned how to form sounds, and only need to learn how to interpret the new information in their brains.

Operation, post-implantation therapy

1½ to 5 hours. First a small area of the scalp directly behind the ear is shaved and cleaned. Then a small incision is made in the skin just behind the ear and the surgeon drills into the mastoid bone and the inner ear where the electrode array is inserted into the cochlea. After 1–4 weeks of healing (the wait is usually longer for children than adults) during which the wound must be kept dry, the implant is turned on or "activated". Results are typically not immediate, and post-implantation therapy is required as well as time for the brain to adapt to hearing new sounds. In the case of congenitally deaf children, audiological training and speech therapy typically continue for years, though infants can become age appropriate—able to speak and understand at the same level as a hearing child of the same age in a matter of months—however it is far more common for the process to take years. The participation of the child's family in working on spoken language development is considered to be even more important than therapy, because the family can aid development by participating actively—and continually—in the child's therapy, making hearing and listening interesting, talking about objects and actions, and encouraging the child to make sounds and form words. Professionals trained to work with children who have received cochlear implants are a major part of the parent-professional team when addressing the task of teaching children to use their hearing to develop speech and spoken language.