Audiological assessment in the selection of cochlear implant candidates

In the UCH/RNID Cochlear Implant Programme, patients referred for further audiological assessment are all post-lingually deafened adults with bilateral hearing losses in excess of 90 dB HL in the frequency range 500 Hz to 4 kHz. The purpose of this assessment as part of the selection procedure for implant candidates is to ascertain whether or not the patient has any residual auditory function which can be aided by conventional means. The procedure includes measurement of thresholds of sensation (whether auditory or vibrotactile) for pure tones, and testing for Uncomfortable Loudness Levels up to 130 dB HL. It also includes measurements of frequency discrimination and abnormal adaptation, and assessment of the effect of acoustic stimulation on tinnitus if present. Those with measurable hearing are further tested for discrimination of simple sound patterns related to the perception of speech. Results of assessment, and criteria of suitability for a trial with a high-powered hearing aid are discussed in this paper. Of the 29 patients tested to date, 14 were judged to have sufficient residual auditory function to justify a hearing aid trial. In 10 cases the trial was successful and these people were then no longer considered to be potential candidates for cochlear implantation.