Sound travels down the ear canal and hits the eardrum. Like the skin of a real drum, the eardrum vibrates when the sound hits it. The vibrations are passed down the chain of bones to the cochlea. The third bone (stapes) vibration cause a piston-like motion that causes the fluid in the cochlea to move. This fluid movement causes the hair cells (the first part of the hearing nerve) to move. When this happens, the hair cells create electrical signals which are picked up by the auditory nerve. The brain interprets the electrical signals as sounds.
A cochlear implant is a surgically implanted device that may restore hearing sensitivity to profoundly deaf or severely hard of hearing people. It consists of an internal device including electrodes threaded into the inner ear or cochlea and an external device or speech processor which includes the microphone, battery and a transmitting coil or headpiece.
How do we hear?
How do cochlear implants work?
Cochlear implants detect sounds via an ear level microphone that conveys these sounds to a wearable sound processor. The processor converts these sounds to tiny digital impulses that provide hearing sensations to the user. Some of the newest sound processors are small enough to fit behind a person's ear. The electronic impulses from the processor are sent to a coil (half- dollar sized) worn externally behind the ear over the implant. The coil sends an FM signal to the implant receiver, located completely under the scalp.
The implant then directs these sound impulses to an array of tiny electrodes within the cochlea (inner ear). In these signals are information about the frequency and loudness of speech and other sounds. The responses to these signals are then conveyed along the auditory nerve to the cortex of the brain where they are interpreted as sound.
How does a cochlear implant differ from a hearing aid?
A cochlear implant bypasses the inner ear and converts acoustical sound into distinctive electrical signals that stimulate the auditory nerve directly and are then interpreted by the brain as sound.
A hearing aid amplifies acoustical sound and, via an earpiece in the external ear, sends the louder sound to the eardrum.
In December 1984, the cochlear implant was approved by the United States Food and Drug Administration to be implanted into adults in the United States. In 1990 the FDA lowered the approved age for implantation to 2 years, then 18 months in 1998, and finally 12 months in 2002, although off label use has occurred in babies as young as 6 months in the United States and 4 months internationally
Who is a candidate for a cochlear implant?
Jefferson Balance and Hearing Center only implants adults (18 years or older). The following are guidelines according to the FDA for cochlear implant candidacy:
- Moderate to profound bilateral sensorineural hearing loss (SNHL)
- No medical contraindications
- HINT sentence recognition of 30% or less in the ear to be implanted and 40% in the other ear for both ears wearing appropriate amplification
- Pre or post lingual (before or after the age of 3) onset of hearing loss
- A strong desire to be part of the hearing world
- Realistic expectations and motivation
- Appropriate family or friend support
What are cochlear implant benefits?
The benefit of a cochlear implant can be a dramatic improvement in hearing. The ability to hear environmental sounds, the improved ability to read lips and in many cases to be able to understand speech and conversations without reading lips and recovering the ability to talk on the telephone are all potential benefits of a cochlear implant. Some people will be able to appreciate and listen to music. A large number of patients can get back into a normal life, return to work and improve their chances for success.
The limitation of a cochlear implant is that not everyone will have dramatic results. For most people who obtain an implant their results may be limited. Not everyone will be able to use the telephone or underhand speech without reading lips, but in most cases the results will be beneficial to the individual receiving the implant. A very small percentage of patients with a cochlear implant may receive no benefit. Natural hearing in the implanted ear in most cases is lost with the placement of a cochlear implant, but usually the hearing results obtained more than makes up for the loss of normal function.
One of the limitations for those who have dramatic or not so dramatic improvement is that once the external processor is removed, there is still deafness.
What is the evaluation process for a cochlear implant?
An appointment will be required with either Dr. Thomas Willcox or Dr. Gregory Artz who are Board certified Neuro-Otologists at Jefferson. The physician will examine the patient and take a thorough history. Further testing will be ordered to determine if an implant is recommended. Additional tests include the following:
- Lab studies to rule out another medical problem
- CAT Scan to evaluate the cochlea and other landmarks
- MRI scan to rule out a central disease
- Auditory evaluation
An evaluation of the auditory system is completed by a board certified audiologist. The testing is performed in a soundbooth and testing is performed with and without the patient’s hearing aids or other more suitable hearing aids. Testing involves hearing tones, words and sentences using appropriate amplification. If the patient is not currently wearing hearing aids, a hearing aid trial may be required
What is the surgical process?
Cochlear implant surgery is typically an outpatient procedure, though some patients may have to stay in the hospital overnight. The surgery is performed under general anesthesia and usually lasts about 3 – 4 hours.
The patient will be seen approximately 10 days following surgery to have sutures removed and to test the implant with the external equipment.
The activation of the external equipment is typically scheduled 3 – 4 weeks after surgery.
What is Activation?
Why does the implant have to be programmed?
The sound processing units must be specially fitted for their users. Audiologists specially trained in programming these devices usually do this. Programming sound processors involves measurement of the individual's sensitivity to the electronic impulses. Other sound quality such as pitch also may be assessed. These responses are used to customize each person's implant system so that sound is as clear and comfortable as possible for them. Quite remarkably, some deafened patients are able to communicate on the telephone the first day. Modern multichannel implants can provide very high levels of sound recognition to many recipients.
What are the FDA approved cochlear implant devices?
Implant: HiRes 90K® with HiFocus Electrode
Sound Processor: Harmony (Behind the Ear)
Cochlear Implant Systems
|Model||90K||Freedom Contour Advance||PULSAR or SONATA|
|Design||Curves||Contour, Straight, Split||Standard, Compressed, Split|
|Material||Silastic||Silastic||Ceramic or Silastic|
|Model||Harmony||Freedom||Opus 1 or Opus 2|
|Batteries (BTE Style)|
|Implant||10 Years||10 Years||10 Years|
|External||3 Years||3 Years||3 Years|