→The different components of cochlear implant are:
→The two main strategies used:
I. Continuous interleaved sampling (CIS): Med-EL(TM) and Clarion (TM)
II. Spectral peak processing (SPEAK): Cochlear(TM)
The patient selection criteria for cochlear transplant surgery have evolved over times as advances in cochlear implant technology produced subsequent improvement in performance outcomes. At any point, however, candidacy resolves around three basic questions:
Initially, only individuals with bilateral profound SNHL with no open set speech recognition were considered candidates for cochlear implants.
|Age of implantation||18 years or Older||Adults and children age 2 years or older||Adults and children age 18 months+||Adults and children age 12 months+|
|Onset of hearing loss||Postinguistic||Postlinguistic adults & pre/postlinguistic children||Pre/postlinguistic adults & children||Pre/postlinguistic Adult and children|
|Degree of SNHL||Profound||Profound||Severe-profound adults profound children||Severe-profound adults, children>2, profound children<2 years|
|Adult speech scores (open set)||0%||0%||40% or less sentences in quiet||50% on sentences in quiet in ear to be implanted, with 60% or less in contralateral ear or binaurally|
|Paediatric speech scores||N/A||0%||Lack of auditory progress, less than 20% paediatric word tests||Lack of auditory progress 30% or less on paediatric word tests.|
The evaluation of candidacy process is a team approach:
CHILDREN (2-17 years)
OTHER CANDIDACY CRITERIA:
The candidates can be divided into three categories. Among these, change over at an earlier age candidates make excellent implants as some plasticity for articulation still remains.
|Postlingual||Onset of deafness has occurred after completion of speech development|
|Perillngual||Onset of deafness has occurred while speech development was occuring|
|Prelingual||Onset of deafness occurred prior to any development of speech
a. Primary candidates: have not acquired language by any other means of communication
b. Secondary candidates: have used another mode of communication (usually sign) to develop language
c. Change over candidates: have developed auditory skulls using a hearing aid.
Post lingual category can be divided into:
In cochlear implant systems, the channel refers to the number of stimulation sites within the inner ear, or cochlea, and is defined by a range of frequencies or pitches. All sounds, ranging from low pitch (bass) to high pitch (treble) sound are separated into the number of available channels. The advantages of multi channel over single channel cochlear implant are:
|Single channel system||Multi channel system|
|Delivery||All sound information is delivered to only one channel.||Divides the incoming sound signal into various frequency bands|
|No. of electrodes||Use single pair of electrodes (signal and ground) through which current passes||Use at least 4 active electrodes to mimie the frequency analyzing capabilities of normal ear (basilar membrane)|
|Area of stimulation||All informationis transmitted to single area of stimulation within the cochclea, regardless of the pitch of the incoming signal.||Incoming information are transmitted to various sites of stimulation spanning the inner ear.|
|Frequency organization||Absent||Low pitch sounds are sent to apical part of the cochlea and high pitch sound to another (basal).Thus sounds are organised by frequency.|
|Insertion and fabrication||Less difficult||Difficult because it needs to be flexible and smooth enough to negotiate the 1st turn of the cochlea without causing extensive damage.|
|Improvement||Performance improvement reach s palteau by 1.5 years post implant||Improvement continues after 2 or more years post implant|
|Miscellaneous(not to write in difference)||> Preferred in patient with severely ossified cochlea which can be prevent a significant insertion depth for the electrode.|
> The possibility of using an ear level device in place of body worn box
> The situation where simplicity of construction and low cost are paramount.
|> multichannel implant is not strongly influenced by:
-Age of onset of deafness when deafness occurs before 3 years .
-Children with congenitial deafness have potential to obtain the sense of benefit as those with acquired loss.