A cochlear implant has changed the lives of thousands of people with hearing impairment all over the world. It is a small, but very complex electronic device that can provide a sense of sound to a patient who is either profoundly deaf or severely impaired and hard of hearing. An implant consists of two parts - an external part that is placed behind the ear and a implant portion that is surgically placed under the skin of the person.
Cochlear implant has the following parts:
• Sensitive microphone (picks up sounds from the environment)
• Speech processor (selects and arranges/filters the sounds picked up by the microphone)
• Transmitter and receiver or stimulator (receive the signals from the speech processor and convert them into electric impulse)
• Electrode array (group of electrodes collecting the impulses from the stimulator and sending them to the auditory nerve)
It’s important to understand that a cochlear implant does not fully restore normal hearing. It can give a impaired or deaf person a useful representation of sounds in the environment, thus helping interact and understand speech.
How exactly cochlear implants do work?
It is important to acknowledge that a cochlear implant works and is significantly different from a hearing aid. A hearing aid amplifes the sound so it may be detected by people with hearing impairment and damaged hearing. Implants however bypass damaged portions of the ear. A cochlear implant directly stimulates the auditory nerve.
Signals that are generated by the implant are sent through the auditory nerve directly to the brain and the signals are recognized as sounds. It is crucial to acknowledge that hearing through a cochlear implant device is different from normal hearing. It usually takes time to learn or relearn, but allows many patients recognize various signals, understand sounds in the environment, and most important - understand speech in person or over the phone.
Who needs a cochlear implant? Who can get a cochlear implant?
Children and adults who are deaf or severely impaired of hearing can benefit from a cochlear implant. Since 2000 cochlear implants have been approved for use in eligible children beginning at 12 months of age. Using a cochlear implant for deaf children in early age, while exposed to sounds during an optimal period to develop speech and language skills, is crucial in helping the youngest patient develop communication abilities. Research has shown that when young patients receive a cochlear implant (followed by intensive therapy) before 18 months of age, they are significantly better able to hear, comprehend sound and music and speak, compared to those who receive implants at older age.
Studies also show that eligible children with cochlear implant before 18 months develop language skills at a rate comparable to children with normal hearing. Many kids succeed in mainstream classrooms.
Some adults who have lost all or most of their hearing later in life also can benefit from using cochlear implants. Many learn to associate the signals from the implant with sounds they remember, incl. speech and without requiring any visual cues such as lipreading or sign language.
How does one receive a cochlear implant? What to expect?
Prior to implantation, all of these factors need to be considered:
Use of a cochlear implant requires surgical procedure and significant therapy and aftercare in order to help learn or relearn the sense of hearing. Not every patient performs at the same level with this device and the decision to receive an implant should involve discussions with medical specialists and experienced cochlear-implant surgeons when possible. Also, the process can be expensive. Some people choose not to have a cochlear implant for a variety of reasons.
Surgical implantations are almost always safe, but it is important to know complications exist and are considered a risk factor in every kind of surgery.
An additional consideration is learning to interpret the sounds created by an implant. This process takes time and practice and speech/language pathologists and audiologists are frequently involved in this learning process.
Surgical procedure and complications rate
The surgical procedure most often used to implant the device is called mastoidectomy with facial recess approach (MFRA).If a person's individual anatomy prevents MFRA, other approaches, such as through the suprameatal triangle are used. A systematic literature review published in 2016 found that studies comparing the two approaches were generally small, not randomized, and retrospective so were not useful for making generalizations; it is not known which approach is safer or more effective.
The procedure is usually done under general anesthesia. Risks of the procedures include mastoiditis, otitis media (acute or with effusion), shifting of the implanted device requiring a second procedure, damage to the facial nerve, damage to the chorda tympani, and wound infections.
The rate of complications is about 12% for minor complications and 3% for major complications; major complications include infections, facial paralysis, and device failure. To avoid the risk of bacterial meningitis, which while low is about thirty times as high compared to people who don't undergo CI procedures, the FDA recommends vaccination prior to the procedure. The rate of transient facial nerve palsy is estimated to be approximately 1%. Device failure requiring reimplantation is estimated to occur in 2.5-6% of the time. Up to one-third of people experience disequilibrium, vertigo, or vestibular weakness lasting more than 1 week after the procedure; in people under 70 these symptoms generally resolve over weeks to months, but in people over 70 the problems tend to persist.
Cochlear implants are only approved for people who are deaf in both ears; as of 2014 a cochlear implant had been used experimentally in some people who had acquired deafness in one ear after they had learned how to speak, and none who were deaf in one ear from birth; clinical studies as of 2014 had been too small to draw generalizations from.
Efficacy
A 2011 AHRQ review of the evidence of the effectiveness of cochlear implants in people with bilateral hearing loss - the device's primary use - found low to moderate quality data that showed: speech perception in noisy conditions was much better for people who had implants in both ears done at the same time, compared to people who had only one; that no conclusions could be drawn about changes in speech perception in quiet conditions and health-related quality-of-life. There was only one good study comparing implanting implants in both ears at the same time, to implanting them sequentially; this study found that in the sequential approach, the 2nd implantation made no change, or made things worse.
A 2012 review found that the ability to communicate in spoken language was better, the earlier the implantation was done; it also found that overall, the efficacy of cochlear implants is highly variable, and that it was not possible to accurately predict which children will and will not acquire spoken language successfully.
A 2015 review, examining whether cochlear device implantation to treat people with bilateral hearing loss had any effect on tinnitus, found the quality of evidence to be poor, and the results variable: overall total tinnitus suppression rates varied from 8% to 45% of people who received cochlear implants; decrease of tinnitus was seen in 25% to 72%, of people; for 0% to 36% of the people there was no change; increase of tinnitus occurred in between 0% to 25% of patients; and in between 0 - 10% of cases, people who didn't have tinnitus before the procedure, got it.
A 2016 systematic review of cochlear implants for people with unilateral hearing loss found that of the studies conducted and published, none were randomized, only one evaluated a control group, and no study was blinded; after eliminating multiple uses of the same subjects, the authors found that 137 people with UHL had received a cochlear implant.
While acknowledging the weakness of the data, the authors found that cochlear implants in people with UHL improves sound localization compared with other treatments in people who lost hearing after they learned to speak; in the one study that examined this, cochlear implants did improve sound localization in people with UHL who lost hearing before learning to speak. It appeared to improve speech perception and to reduce tinnitus.
A 2015 literature review on the use of cochlear implants for people with auditory neuropathy spectrum disorder found that description and diagnosis of the condition was too heterogeneous as of that date, to make clear claims about whether cochlear implants is a safe and effective way to manage it.
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