Cochlear Implantation for Treatment of Single-sided Deafness

Inclusion Criteria: * 18 years of age or older with the ability to provide informed consent * English as the primary language * Medically and psychologically suitable * Willing to receive/have received meningitis vaccinations * Able to pay for all care received through the study, either through the subject's insurance company or through self-pay * Able to comply with study requirements, including travel to the investigational sites * Severe to profound sensorineural hearing loss (≥70 dB HL (decibel hearing level) thresholds between 500 and 4000 Hz) in the worse ear with ≤ 20% Consonant-Nucleus-Consonant (CNC) word scores * Duration of single-sided deafness ≥ one year * Tinnitus localized to the affected ear, both ears, or in the head localized to the affected ear, both ears, or in the head * Expected subjects include those with: * Unilateral hearing loss secondary to viral or bacterial infection, such as meningitis or labyrinthitis * Ménière's disease * Sudden sensorineural hearing loss * Vascular disease affecting the inner ear * A combination of any number of the above conditions Exclusion Criteria: * Duration of single-sided deafness ≥ ten years * Pure tone thresholds ≥ 35 dB HL at 500, 1000, 2000, and 4000 Hz in the better ear * Consonant-Nucleus-Consonant (CNC) word scores ≤ 70% in the better ear * Chronic otitis media in either ear * Inner ear malformation in either ear * Autoimmune inner ear disease (fluctuation sensorineural hearing loss in either ear) * Evidence of retrocochlear pathology, including vestibular schwannoma * Unilateral tinnitus in the unaffected ear * Cochlear ossification * Demonstrated cognitive and/or developmental challenges * Major depression or anxiety; post-traumatic stress disorder; substance abuse * Medical or psychological conditions that serve as contraindication to surgery * Additional handicaps that would prevent or limit participation in evaluations * Unrealistic patient or family expectations regarding the benefits, risks, and limitations inherent to the procedure and the prosthetic device * Pregnant women: The investigators will specifically ask all women of childbearing age if there is a possibility they are pregnant or trying to become pregnant at the initial clinic visit; any women who are pregnant or actively trying to become pregnant will be excluded. In cases that are questionable on the day of planned surgery, a pregnancy test will be performed as per current Massachusetts Eye \& Ear Infirmary anesthesia pre-operative protocols.