The Majestic Invention – The truth about Cochlear Implants
“Blindness cuts us off from things, deafness cut us off from people”. Hearing loss (HL) limits one from interacting with one’s peers, and so impacts the ability to participate in social and workplace interactions. It limits learning and professional activities. As per WHO estimates in India, there are approximately 63 million people, who are suffering from significant auditory impairment. This shows the estimated prevalence at 6.3% in Indian population.
Cochlear implants are electronic devices that provide useful hearing & improved communication abilities. This would be helpful for the persons who have severe to profound sensorineural hearing loss. A cochlear implant electrically stimulates the auditory nerve inside the inner ear. In the inner ear, that is in cochlear, we are directly implanting the device.
There are two parts of cochlear implants, they are external and internal.
- External part consist of an external audio processor and a transmitter.
- The internal part are comprises the receiver/stimulator package along with an electrode array.
- The internal receiver is implanted surgically under the skin behind the ear whereas the external audio processor is worn like a hearing aid.
WORKING OF A COCHLEAR IMPLANT
The basic working steps are:
- The sound processor captures the sound and converts it into digital information.
- This digital information is transmitted to the receiver which is placed just under the skin, behind the ear.
- Here the digital information is converted back to electrical signals and sends them along the electrode array.
- The implant array(i.e. the electrode array) is positioned within the cochlea.
- The electrodes present along the implant array can give small electrical pulses to the specific part of the cochlea.
- This triggers the auditory nerve, to produce hearing sensations.
SURGERY PROCEDURE OF COCHLEAR IMPLANT
The surgery is carried out under general anaesthesia. There are broadly two surgical techniques:
The facial recess approach and the pericanal technique.
- The facial recess approach:
- At first, a simple cortical mastoidectomy is done followed by the short process of the incus and the lateral semicircular canal is identified.
- A posterior tympanotomy is performed by opening the facial recess.
- Identification of the stapes, promontory and round window is done.
- Cochleostomy is performed antero-inferior to the round window membrane to a diameter of 1-1.6mm depending on the electrode used.
- The pericanal technique:
- In this, a tympanomeatal flap is elevated to perform a cochleostomy either by endaural or postaural approach.
- A bony tunnel is drilled along the external canal towards the middle ear.
SUCCESSFUL OUTCOMES OF COCHLEAR IMPLANTATION:
- Shorter duration of deafness
- Recognition of environmental sounds regularly
- Able to listen in a noisy environment
- Able to find where the sound is coming from
- Symptoms of ringing in the implanted ear
COMPLICATIONS OF COCHLEAR IMPLANT
Complications are rare and can include:
- Facial paralysis
- Infection at the surgery site and device infection
- Spinal fluid leak
- Tinnitus (new or worsened ear noise)
- Otitis media
- Migration/displacement of device
- Flap necrosis
Risks of cochlear implants include:
- Loss of residual hearing: this implantation of device can cause a loss of any remaining, unclear, natural hearing in the implanted ear.
- Inflammation of the membranes surrounding the brain and spinal cord (meningitis).
- Failure of device: this occurs in less than 5% of people over many years.
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