Patient selection

The selection of a person for a cochlear implant follows a rigorous protocol specified by the Cochlear Party Inc.  This is to ensure maximum benefit from the surgery and the device.  The patient needs to undergo a thorough E.N.T. evaluation to rule out any contraindications for the surgery.  A detailed audiological evaluation should be done to confirm the profound degree of sensory neural deafness in both the ears.  This should be  followed by a hearing aid trial and optimisation of hearing aid fitting.

An aided audiogram and speech discrimination with the selected hearing aid would be determined and re-determined after at least six weeks of using the hearing aid.  This procedure is required even if the hearing aid does not offer any significant benefit to the patient.  This is to ward off the criticism that the patient has been fitted with the cochlear implant without determining the effectiveness  of a suitable hearing aid.  A patient receiving little or no benefit with an optimised hearing aid selection procedure would be considered an ideal candidate for the implant.  A CT scan would assist the surgeon overcome problems, if any, with electrode insertion into the cochlea.

It takes about three or five weeks for the incision made for the implantation to heal.  The patient is now ready for the “switch on” of the device by the audiologist.  “Switch on “ “involves fitting the external headset and programming the speech processor.  The speech processor has to be individually programmed because the current required for sensation of hearing varies for electrodes implanted and also from patient to patient.  The programming or “MAP” ping” as it is technically known is done by a specially trained audiologist.  The mapping is done by using a diagnostic programming system and necessary software installed in the clinic.

The audiologist during mapping, establishes the T-levels, C-levels for each electrode and balancing loudness of all the electrodes.  The T-Level is the level at which the patient just perceives the sound sensation.  The C-level is the maximum stimulation level not  causing discomfort.   Balancing loudness ensures a smooth sound perception.  The MAP  thus created is a complete set of instructions to the speech processor to encode the signals which are to be presented to the electrodes.  The MAP is written into the memory of the speech processor and becomes active when the speech processor is switches on.  The audiologist would create new MAPs subsequently, comparing them with the MAP in the speech processor to provide the one best suited to the patient.