Baseline Hearing Levels Post-Surgery for the Southern Cochlear Implant Program

Abstract

This study aims to obtain baseline data on the levels of post-surgery acoustic hearing for adult cochlear implant (CI) users in the Southern Cochlear Implant Program (SCIP), and to compare these to their pre-surgery hearing levels. The surgical techniques for implanting the CI are constantly being improved, with current trends aiming to preserve as much residual hearing as possible. Up until 2007, no specific measures were employed by surgeons involved with the (SCIP) to preserve residual hearing during the implantation procedure. It is hypothesised that: i ) Although post-surgery hearing thresholds will be significantly lower than pre-surgery levels, numerous patients will still have some degree of residual hearing remaining in their implanted ear; and ii) That participants with greater levels of residual hearing in the implanted ear will perform better on speech perception tests. The study included 25 postlingually-deafened adults (18 yrs and above) who were implanted through the SCIP, and who had pre-surgery hearing levels of 100dB or better at 250, 500 & 1000 Hz. There were 6 males and 19 females with a mean age of 57.4 years (SD = 13.89). Their average experience with a CI was 28.12 months (SD = 19.14). Hearing thresholds using puretones as well as speech perception of the participants was assessed. The Consonant-Nucleus-Consonant (CNC) test for words as well the Hearing-In-Noise Test (HINT) for sentences were used to assess speech perception. The mean post-surgery puretone average (PTA) (i.e. average of hearing thresholds of 250, 500, 1000 & 2000 Hz) was found to be 117 dB HL, as compared to 89 dB HL presurgery. Thirteen of the 25 participants (52%) presented with measurable levels of acoustic hearing levels in their implanted ear. The participants showed significant improvement in their pre-surgery to post-surgery speech perception scores in quiet (Sentences: pre- 19%; post- 82%. Words: pre- 7%; post- 55%).However, participants with greater levels of residual hearing in the implanted ear did not perform better on speech perception tests. These speech perception results suggest that the current implant recipients from the SCIP are obtaining significant improvement in speech perception outcomes post-surgery. Results suggest that hearing can be preserved in CI surgery even without specific techniques being employed. Therefore, there is a potential for greater levels of hearing to be preserved if surgeons start to use modified techniques. This may impact on pre- and post-surgery clinical counselling, as well as when determining the future CI candidacy criteria.