Hearing and Structure Preservation Via ECochG

Inclusion Criteria: * Aged 18 years of age or older * Within cochlear implant inclusion criteria by local regulations/guidelines at the time of implantation * Severe to profound hearing loss (average air conduction unaided hearing threshold of ≥ 70 dB HL for 500, 1000, 2000 and 4000 Hz) in the ear to be implanted * Air conduction unaided hearing threshold ≤ 70 dB HL at 500 Hz in the ear to be implanted * Less than 15 years of severe to profound deafness on the implant ear prior to surgery * Post-lingually acquired hearing loss in the ear to be implanted * Normal cochlear anatomy as confirmed by pre-operative imaging in the ear to be implanted * Listed for an Advanced Bionics HiRes Ultra (3D) HiFocus SlimJ electrode array * Listed for cochlear implant surgery under general anaesthesia * Fluent in local language * Given informed consent to participate in the study Exclusion Criteria: * Abnormal cochlear anatomy (including ossification) as identified by pre-operative radiological evaluation in the ear to be implanted * Any pre-existing cochlear or middle ear pathology, such as otosclerosis, cholesteatoma, or previous middle ear surgery in the ear to be implanted * Any medical conditions that would increase the risk of local complications during cochlear implantation, such as autoimmune diseases or active local infections * Diagnosis of auditory spectrum neuropathy disorder * Deafness due to lesions of the acoustic nerve or central auditory pathway * Deafened by meningitis * Single sided deafness (average for 500, 1000, 2000 and 4000 Hz in the better ear ≤ 30 dB HL) * Asymmetric hearing loss (average for 500, 1000, 2000 and 4000 Hz in the better ear \> 30 dB HL and ≤ 55 dB HL) * History of previous cochlear implantation/re-implantation on either ear * Any contraindications to computed tomography (CT) scans * Concurrent participation in other cochlear implant related studies