The cochlear implant is an electronic device that restores hearing to the totally deaf. Part of it is surgically implanted in the ear (temporal bone), and part is worn externally like a hearing aid. It is a medical device that bypasses damaged parts of the inner ear and electronically stimulates the nerve of hearing.
Normal Hearing
The ear is divided into three parts: external ear, middle ear, and inner ear. Each part performs an important function in the process of hearing. Sound travels along the ear canal of the external ear and causes the ear drum to vibrate.
The three small bones of the middle ear ( Malleus, Incus, and Stapes) conduct this vibration from the ear drum to the cochlea or auditory chamber of the inner ear. Fluid waves in the cochlea, initiated by movement of the three small ear bones, stimulate more than sixteen thousand delicate hearing cells (hair cells).
Movement of these hair cells generates an electrical current in the auditory nerve. This current is transmitted through various complicated inter connections in the brain stem to the part of brain that recognizes these electrical stimulation as sound.
Types of hearing impairment
When there is a disease or obstruction in the external or middle ear, a conductive hearing impairment results. This impairment may be due to a variety of problems and may be corrected by medical or surgical treatment
When the hearing impairment is due to a problem in the inner ear, a sensorineural impairment results. In most cases of sensorineural hearing loss, the hair cells have been damaged and do not function.
Although many of auditory nerve fibers may be intact and capable of transmitting electrical impulses to the brain, without functioning hair cells the nerve fibers remain unstimulated. Sensorineural hearing loss cannot be corrected medically.
How Cochlear Implants Work?
Cochlear Implants are designed to bypass the hair cells which are not functioning and provide stimulation directly to the auditory nerve. These are a number of different cochlear implants currently available.All cochlear implant systems consist of a microphone, a signal processor, a signal couple (transmitter and receiver) and electrodes that are implanted in the cochlea.
The microphone and signal processor are worn outside the body, like a hearing aid and the receiver and the electrode will be placed inside surgically, it won’t be visible after surgery. The electrical stimuli are sent inside the body to the implanted electrodes. The electrical signals stimulate the auditory nerve fibers and the signal is then sent to the brain.
Who is a Cochlear Implant Candidate?
The cochlear implant is designated only for individuals who receive little or no benefit from hearing aids. Becoming a cochlear implantee involves an evaluation, including otologic, audiologic, radiographic and psychological tests:
Ear (Otologic) Evaluation:
Ear examination must be performed to assure there is no active infection or other problem within the middle or inner ear that would preclude the surgical placement of the implant.
Hearing (Audiologic) Evaluation:
Extensive hearing tests must be performed to determine the degree of hearing with and without a hearing aid. Special tests are performed to evaluate benefits from hearing aids.
Imaging (Radiographic) Evaluation:
Special imaging, usually computerized tomography (CT) & MRI are taken to evaluate the condition of the inner ear bone and auditory nerve.
Neuro Psychological Evaluation:
Psychological evaluation is required for some cochlear implant children.
Physical Examination:
A general physical examination is performed to identify possible problems with general anaesthesia or surgical implantation of the electrode assembly.
Cochlear Implant Surgery
Cochlear implant surgery is performed under general anaesthesia. An incision is made behind the ear. The mastoid bone is opened, leading to the middle ear. The operation takes from 1 to 3 hours depending on the specific cochlear implant being used. The hospital stay varies 1 to 3 days, depending on the device used and patient’s needs.
Postoperative Care, Training and Follow-up
The patient returns to the implant clinic two to three weeks following surgery and is fitted with the external portions of the device (sound processor, microphone and transmitter). Instruction regarding care and maintenance of the system and training in listening to sound through the implant are provided at that time.
Cochlear implant program duration differs with age of fitting of implant and amount of training provided. In addition, patients are usually required to continue returning to the clinic at regular interval for check-up and assessment.
What to Expect from a Cochlear Implant?
Cochlear Implant provides near to normal hearing to the hearing impaired who gets limited or no benefit from usual hearing aid. The majority who receive a cochlear implant are able to learn speech and language and communicate like any other normal individual.
Results vary for different individuals, depending on factors such as age at time of deafness, age at implant surgery, duration of deafness, status of the remaining auditory nerve fibers, training etc.
The cochlear implant clinics explain reasonable expectations for each situation. It is important to clearly understand the time commitments before making a decision about the cochlear implant. There is a small number of patients for whom a cochlear implant is not beneficial.
Cost of Cochlear Implant-cochlear implant price
A cochlear implant is considerably more expensive than a hearing aid. Cost of Cochlear Implant is approx Rs 13,00,000 and half of expense is covered by Nepal Government.
Dr Ravi Bhushan Suwal,MS(ENT),
Fellowship in Cochlear Implant Surgery