Prognosis in unilateral and bilateral cochlear implantation

In the first part of this thesis, the results of a retrospective cohort study and a systematic
review on prognostic factors in unilateral cochlear implantation (UCI) are presented. This thesis underlines that, in adults, age at implantation is not a predictor for post-implant speech perception scores. A large part of the variation in post-implant speech perception scores is left unexplained,
likely due to the factor of spiral ganglion cells degeneration. In addition, bony disorders
such as meningitis and otosclerosis have a negative association with post-implant speech
perception scores. When a patient has symmetrical deafness and no factors that favor
one ear over the other ear for implantation, we advise to implant the right ear based on a
phenomenon called ‘the right ear advantage’.
In the second part of this thesis, the results of a randomized controlled trial are presented on the difference between UCI, simultaneous bilateral cochlear implantation (BiCI) and sequental BiCI. The results underline the clinically relevant benefits of BiCI over UCI on speech perception in noise and localization abilities. Furthermore, this thesis found hints of advantages of simultaneous BiCI over sequential BiCI, especially on a higher order phenomenon called the squelch effect. Our studies on the squelch effect were hindered by small sample sizes and therefore needs corroboration from future studies. No disadvantages were seen from sequential BiCI, leading the way to sequential BiCI in unilateral CI users. Future cost-utility studies in CI users should use hearing related outcome measures.