Outcomes of Cochlear Implantation in an Auditory Deprived Ear

i Abstract This thesis challenges the assumption that poor functional outcomes are likely to be obtained when a cochlear implant is placed in an ear with long-term auditory deprivation. While previous research has shown that poor outcomes tend to be associated with long-term deafness and poor residual hearing in both ears, outcomes have not been examined in cases where implantation is performed in the sounddeprived ear of individuals with long-term asymmetric hearing; that is, individuals still receiving benefits from a hearing aid in the other ear. As suggested in functional imaging studies, it is possible that input from one ear could maintain synaptic activity within the auditory pathways and cortex, and contribute to outcomes obtained with the implant placed in the long-term sound-deprived ear. The research described in this thesis is based on five retrospective cohort studies (n=10 to 151) using different methodologies. It examines speech recognition scores obtained after cochlear implantation in adults with a long-term (≥15 yrs) monaural sound deprivation (bilateral hearing loss aided monaurally). In order to increase the sample size and applicability of the findings, analysis is based on data collected in five implantation centres, located in Australia, Canada, and Sweden. The results of the studies demonstrate that adults with an acquired hearing loss and monaural sound deprivation can obtain similar outcomes with the implant placed either in the sound-deprived or aided ear. These results occur regardless of the duration of sound deprivation in the implanted ear. However, for adults with a prelingual hearing loss, poorer outcomes typically occur when implanting the sounddeprived ear compared with the aided ear. The duration of bilateral significant hearing loss appears to be the most reliable predictor of implantation outcomes in a sound-deprived ear. Furthermore, the results of the studies suggest that the duration of sound deprivation in the implanted ear should not be considered as a relevant variable for clinical decision-making, with regards to speech recognition score outcomes. It is anticipated that these results will influence clinical guidelines and offer new insight into auditory plasticity and contributors to outcomes of cochlear implantation.