The Clarion Electrode positioner: approximation to the medial wall and current focussing?

In order to establish whether the electrical field created by a cochlear implant electrode is more focussed in a perimodiolar than in a medial position, voltages at non-stimulated electrodes were collected from the Clarion 1.2 implant before and after insertion of the Clarion Electrode Positioning System. The positioner is inserted lateral to the electrode array and is intended to bring the array close to the medial wall of the scala tympani. These intracochlear electrode voltages (IEVs) were collected in 9 surgeries with the HiFocus I electrode array with positioner. Stapedius reflex thresholds were decreased after insertion of the positioner on 20 out of 22 electrodes. Electrode impedances did not increase significantly. IEVs increased slightly for all stimulated electrodes. However, the positioner did not significantly affect the slope of the IEVs for any of the stimulated electrodes. Individual differences between patients in the mean IEV amplitude were considerable; 2 patients deafened by otosclerosis showed particularly low amplitudes. Thus, IEVs provided no evidence of a focussing of the electrical field by introducing the positioner. Possible benefits of a perimodiolar position regarding efficiency and channel separation are discussed in terms of a reduced distance between electrodes and neural elements.