Safety and Efficacy of the Cochlear Nucleus CI422 Cochlear Implant in Adults

Inclusion Criteria: 1. Eighteen years of age or older at the time of implantation 2. Moderate low frequency thresholds up to and including 1000 Hz, severe to profound high frequency (above 3000 Hz) sensorineural hearing loss 3. Minimum of 30 days experience with appropriately fit bilateral amplification, fit using the standardized National Acoustics Laboratory (NAL) fitting method described in the Fitting and Use of Hearing Aids section below 4. Aided Consonant Nucleus Consonant (CNC) word recognition score (mean of two lists) between 10% and 50%, inclusive in the ear to be implanted 5. Aided CNC word recognition score (mean of two lists) in the contralateral ear equal to, or better than, the ear to be implanted but not more than 70% 6. Willingness to use bimodal stimulation (i.e., a cochlear implant on one ear and a hearing aid on the contralateral ear) through at least 6-months postactivation 7. English spoken as a primary language Exclusion Criteria: 1. Duration of severe-to-profound hearing loss greater than 30 years 2. Congenital hearing loss (for the purpose of this study, onset prior to 2 years-of-age) 3. Medical or psychological conditions that contraindicate undergoing surgery as determined by the Investigator 4. Ossification or any other cochlear anomaly that might prevent complete insertion of the electrode array 5. Conductive overlay of 15 decibels (dB) or greater at two or more frequencies, in the range 500 to 1000 Hz 6. Deafness due to lesions of the acoustic nerve or central auditory pathway 7. Absence of cochlear development 8. Diagnosis of auditory neuropathy 9. Active middle-ear infection 10. Tympanic membrane perforation in the presence of active middle ear disease 11. Unrealistic expectations on the part of the subject, regarding the possible benefits, risks, and limitations that are inherent to the surgical procedure(s) and prosthetic devices as determined by the Investigator 12. Unwillingness or inability of the candidate to comply with all investigational requirements as determined by the Investigator 13. Additional handicaps that would prevent or restrict participation in the audiological evaluations as determined by the Investigator