A Comparison of Electrical Stimulation Levels Across Ears for Children With Sequential Bilateral Cochlear Implants

Objectives: To compare threshold and comfortable levels between a first and second cochlear implant (CI) for children, and to consider if the degree of difference between CIs was related to the age at bilateral implantation or the time between implants. A secondary objective was to examine the changes in levels over time for each CI . Design: Fifty-seven participants were selected from the 146 children and young adults who received a first Nucleus CI as a child, and received a second implant at the Royal Victorian Eye and Ear Hospital between September 2003 and December 2011. Exclusion criteria included an older implant type, incomplete array insertion, incomplete data available, and a pulse width higher than the default. Using measurements from clinical sessions, the threshold levels, comfortable levels, and dynamic range of electrical stimulation were compared at three electrode array regions and at the "initial" (first 10 weeks), 2-year, and 5-year postoperative time points. The T-ratio and C-ratio for each array region and each time point were calculated by dividing each mean (n = 3 electrodes) level for the second implant by that for the first implant. Results: The T-ratio was generally not significantly different to one, indicating no differences in threshold levels between the second and first implants; however, threshold levels were lower for the second implant in the apical region at the initial time point, and there was a significant difference in threshold levels in the apical region for children with a Contour Advance array for the second implant and an older-style array (i.e., Contour) for the first implant. For each implant individually, there were no significant changes in threshold levels across time. The C-ratio was significantly

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