The Cochlear Implants have become established management options for profound sensorineural deafness. Even the WHO has endorsed it. However, there are no technical advancements as far as the functioning of CIs concerned in the last two decades. All that we have seen is cosmetic and ergonomic developments such as a reduction in the size of the receiver-stimulator, stringless processors, or waterproof accessories. Only notable progress is in the configuration of the electrodes. Now many varieties of electrode arrays are available with existing vendors. There are few specific suggestions of electrode arrays for abnormal cochlea. However, there are no clear guidelines for the choice of electrodes arrays to the normal cochlea. There is also considerable debate about the approach (Facial recess vs. Veria) and routes of electrode insertion (Round window vs. Cochleostomy). The affordability of the patient, availability of resources, and alignment of surgeons with specific companies have been determining factors in developing countries.
I found this paper while preparing a presentation on eCAPS, delivered to a group of engineers. “Electrically evoked compound action potentials are different depending on the site of cochlear stimulation” is a multi-author, multi-center sans India, study. The use of electrically evoked compound action potentials (ECAPs) has become an inevitable part of CIs. The recording of ECAPS and its applications has been well established. It is already a well-known fact that the eCAP amplitude differs between the basal, middle, and apical regions. There are several hypotheses based on the anatomy of the cochlea and electrode array design in support of this claim. This entire paper can be summarised in one sentence, “eCAP recordings in the apical region of the cochlea are useful.” The authors attribute these findings to more prominent amplitude responses and steeper slopes at the apex of the cochlea, which are most likely due to both higher neural survival and the proximity of stimulating electrode to the modiolar wall.
Sometimes clinicians wonder about the significance of papers on basic sciences – the electrophysiological studies in their clinical practice. Positively, the findings of this research have major implications for hearing preservation during CI and future electrode array designs. We can expect a few more technical advances in electrode array designs soon. I have also noticed in a few large centers that they choose the electrode array based on such observations. While they use a slim straight electrode introduced via the round window for patients with significant residual hearing, they use perimodiolar electrode arrays inserted through a cochleostomy for other cases.