“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.

Cochlear implants can be used for the people who may not get benefitted with the hearing aids. An hearing aid amplifies the sound whereas cochlear implant bypasses the damaged portions to deliver the sound directly to the auditory nerve.

There are two components of cochlear implants, they are external components and internal components.

  • External components consist of an external audio processor and a transmitter.
  • The internal components are surgically implanted and comprises of the receiver/stimulator package with an electrode array.

WORKING OF A COCHLEAR IMPLANT

A cochlear implant system consists of an audio processor worn behind the ear. This processor captures the sound from the surrounding environment and sends them to the receiver implanted under the skin behind the ear. The receiver in turn sends the signals to the electrode array that is inserted in the cochlea.

The basic working steps are:

  1. The sound processor captures sound and converts it into digital code.
  2. The sound processor transmits the digitally coded sound through the coil to the implant just under the skin.
  3. The implant converts the digitally coded sound to electrical signal and sends them along the electrode array which is positioned in the cochlea.
  4. The implant’s electrodes stimulate the cochlea’s hearing nerve fibres, which relay the sound signals to the brain to produce hearing sensations.

The sounds are captured by the processor’s microphone and they are digitized and processed by the processor. The information coded by the processor is sent to the implant via the antenna. The implant converts the information into electric signals and sends them to the electrodes. Each electrode corresponds to a tone frequency band (high and low pitched) and delivers electrical impulses to the auditory nerve as the ciliated cells should do. The auditory nerve transmits this information to the brain. The brain interprets the signals as sounds and so on hears.

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.

  1. 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.
  2. 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:

  • Bleeding
  • Facial paralysis
  • Infection at the surgery site and device infection
  • Dizziness
  • Spinal fluid leak
  • Tinnitus (new or worsened ear noise)
  • Otitis media
  • Migration/displacement of device
  • Flap necrosis
  • Meningitis

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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