Investigation to Evaluate the Safety and Effectiveness of Cochlear Implantation in Children and Adults With Unilateral Hearing Loss/Single-sided Deafness

Inclusion Criteria: • Individuals 18 years or older (Group A) Ear to be Implanted: Severe sensorineural hearing loss (HL) defined as: Pure-tone average at 0.5, 1, 2, 4 kHz \>80 dB HL ; Aided Consonant-Nucleus-Consonant Test (CNC) score ≤5% and Normal Hearing Ear: Normal or near normal hearing defined as an average of (0.5, 1, 2, 4kHz) ≤ 30 dB HL • Children 5 years to 17 years, 11 months (Group B) Ear to be Implanted: Severe sensorineural HL defined as: Pure-tone average at 0.5, 1, 2, 4 kHz \>80 dB HL; Aided CNC score ≤5% and Normal Hearing Ear: Normal or near normal hearing defined as an average of (0.5, 1, 2, 4kHz) ≤ 30 dB HL * Previous experience with a current conventional treatment option for unilateral \[SSD\] HL (HA, bone-conduction device, or CROS technology), if no previous experience a minimum trial period of two weeks is required * English spoken as a primary language * Willing and able to provide written informed consent Exclusion Criteria: * Ossification, abnormal cochlear nerve or any other cochlear anomaly that might prevent complete insertion of the electrode array * Previous cochlear implantation * Hearing loss of neural or central origin, including auditory neuropathy * Duration of profound sensorineural HL \>10 years per self-report * Active / chronic middle-ear infection; conductive HL in either ear * Medical or psychological conditions that contraindicate undergoing surgery as determined by the Investigator * Unrealistic expectations on the part of the participant/family, regarding the possible benefits, risks, and limitations that are inherent as determined by the Investigator * Evidence of and/or suspected cognitive or developmental concern * Unable or unwilling to comply with the requirements of the clinical investigation as determined by the Investigator * Investigator site personnel directly affiliated with this study and/or their immediate families; immediate family is defined as a spouse, parent, child or sibling * Cochlear employees or employees of Contract Research Organizations (CROs) or contractors engaged by Cochlear for the purposes of this investigation * Pregnant or breastfeeding women * Currently participating, or participated within the last 30 days, in another interventional clinical investigation/trial involving an investigational drug or device.