Cochlear implantation as an approved clinical therapy ushered in an exciting era of innovation for the treatment of hearing loss. The U.S. Food and Drug Administration approved the use of cochlear implants as a treatment option for adults with profound sensorineural hearing loss in 1985. The landscape for treating adults and children with significant hearing loss has changed dramatically over the last three decades. The purpose of this paper is to examine the evolving regulatory process and changes to clinical care. A significant emerging trend in cochlear implantation is the consideration of steroids to preserve hearing during and following surgery. This parallels the quest for hearing preservation in noise-induced hearing disorders, especially considering the current interest in biological drug therapies in this population. The future will likely usher in an era of combination therapeutics utilizing drugs and cochlear implantation. For over 30+ years and following regulatory compliance, the Rocky Mountain Ear Center has developed an extensive candidacy and outcome assessment protocol. This systematic approach evaluates both unaided and aided auditory performance during candidacy stages and post-implantation. Adjunctive measures of cognition and quality-of-life augment the auditory assessment in specific populations. Practical insights into lessons learned have directed further clinical research and have resulted in beneficial changes to clinical care.

Cochlear implants are prosthetic devices with the potential to restore hearing ability in those individuals with significant hearing loss. The advent and evolution of the cochlear implant have led to a complete change in the approach to treating patients with severe-to-profound hearing loss. Up to the middle of the twentieth century, deafness constituted a condition the medical world could not overcome. Presently, cochlear implants restore hearing sensation to the point where many recipients detect sounds at similar levels to individuals with normal hearing, although hearing with a cochlear implant is not analogous to normal hearing. As a result of significantly improved audibility, cochlear implantation has ultimately become the method of choice in the treatment of profound hearing loss.1 

In the years since the U.S. Food and Drug Administration's (FDA) 1985 approval for use of cochlear implant devices in adults with hearing loss, the real-world landscape of this technology has continuously evolved, and implant indications have been considerably modified. The initial clinical criteria for implantation were quite narrow and included only profound bilateral sensorineural hearing loss.2,3 Today, the spectrum of approved indications has widely expanded as the benefits have become more broadly demonstrated, clinically documented, scientifically confirmed, published, and appreciated by the general public.4–7 

Since the early established criteria, several subsequent FDA-approved and monitored new Investigational Device Exemption (IDE) clinical trials have led to marked improvements and technical advances in commonly used implants. In a parallel manner, the standard testing batteries employed for patient evaluation began to change significantly. The present report will describe the main historical sequence of events in these regulatory and clinical factors including the evolution of therapeutic criteria, device modifications and testing instruments. In addition, the development of the Rocky Mountain Ear Center (RMEC) pre- and post-operative protocol guidelines will be outlined and future directions in the overall field of cochlear implantation will be considered.

The experiences in the development of cochlear implantation and refinement of the implant technology to bring about better hearing are informative for the development of treatments for other types of hearing dysfunction such as noise-induced hearing loss. The evolving candidacy requirements for implantation are demonstrative of the abilities of an established technology that, with careful evaluation, application, and development, can address certain levels and configurations of hearing loss. The evolution of these protocols is revealing of how therapies for other types of hearing loss may eventually progress including the base technology for such therapy, assessments that have been used, as well as their limitations. The evolution of such complementary approaches has specific significance for hearing monitoring during clinical trials of ototoxic drugs or those that are used to treat noise-induced hearing loss including biological therapies.8,9

In the early 1980s, the FDA approved a single-channel implant for adults (House/3M single-channel device), which consisted of a receiver/stimulator and a single-channel electrode inserted into the cochlea. The recipient was fitted with a body-worn sound processor (external device) that housed a microphone and power supply. Early developers of this technology encountered skepticism and resistance from the scientific community. The single-channel device provided recipients with an improved quality-of-life and significantly improved lip-reading abilities compared to when the recipient was not using their single-channel device.2 Single-channel cochlear implantation also provided improved environmental sound awareness and better modulation of the recipient's voice.10 However, this initial single-channel technology was not able to provide the spectral and temporal cues required for developing open-set speech perception abilities that relied entirely on audition.

Utilizing the tonotopic arrangement of the cochlea, several scientists across the globe, but predominately in California, began to develop multi-channel implants to broaden the range of available spectral and temporal cues. From the 1960s to the 1970s, William House in Los Angeles developed an original 5-wire implant, Blair Simmons of Standard University developed a 6-electrode implant, and Robin Michelson, Robert Schindler, and Michael Merzenich at the University of California, San Francisco developed a multi-channel implant system which was acquired by Clarion.11 In Australia, Dr. Graeme Clark developed a cochlear implant that provided the framework for the first FDA-approved multi-channel device. This implant, Cochlear Ltd.'s Nucleus 22 device, consisted of a receiver/stimulator (internally implanted device) that housed 22 banded electrodes, and a body-worn sound processor. A long cable attached the body-worn processor to a microphone and a shorter cable connected the microphone to an external transmitter.2 The multi-channel technology became a standard feature of the modern FDA-approved cochlear implant systems from Cochlear Ltd., Med El GmbH, and Advanced Bionics.

Several other companies worldwide have developed single-channel (Vienna/3M) and multi-channel devices at similar time points (Clarion, Med El). Some of these clinical trials did not lead to viable clinical solutions. With the emergence of these multiple devices, slightly different FDA indications relative to the degree of hearing loss and speech recognition scores were established for each manufacturer. The variability of indications approved by the FDA has impacted the refinement of protocols and complicated the ability to develop a single patient candidacy protocol. For example, there are currently three cochlear implant companies that were granted FDA approval, but each has different labeling for their devices (Tables I–III). Insurance companies typically follow broader FDA guidelines and do not necessarily agree to pre-authorize a surgical procedure based on individual manufacturer indications. For example, Advanced Bionics received FDA approval for use in adult candidates with severe-to-profound bilateral sensorineural hearing loss. However, Cochlear Corporation received FDA approval for use in adults with moderate-to-profound sensorineural hearing loss. Insurance companies will typically pre-authorize surgery for adults with moderate-to-profound bilateral sensorineural hearing loss regardless of which manufacturer the patient chooses. The FDA indications followed by many private insurance companies for pre-authorization of a cochlear implant surgery generally take into consideration the most liberal labeling available in order to have the most people benefit from the technology as possible. Conversely, in some cases, agencies such as Medicare, have previously assumed a much more conservative coverage policy, requiring that older (≥65 years of age) candidates demonstrate a poorer sentence score (40%) in the best-aided condition compared to younger (under 65 years of age) candidates who are allowed by most private insurers to obtain a score of 60% in the best-aided condition. Additionally, Medicare denies coverage for adults with single-sided deafness, while many private insurance companies provide coverage to these individuals. In September 2022 Medicare expanded candidacy criteria following the Centers for Medicare and Medicaid Services (CMS) recent recommendations; however, it is anticipated that Medicare coverage will not be as liberal as private insurance companies for single-sided deafness. Insurance coverage considerations further complicate the refinement and development of candidacy and assessment protocols.

TABLE I.

Adult and pediatric cochlear implant candidacy (Advanced Bionics).

Adults Children
– 18 years of age or older  – 12 months through 17 years of age 
– Severe-to-profound, bilateral sensorineural hearing loss (>70 dB HL)  – Profound, bilateral sensorineural deafness (≥90 dB HL) 
– Use of appropriately fitted hearing aids for at least 6 months in children 2 through 17 years of age, or at least 3 months in children 12 through 23 months of age. The minimum duration of hearing aid use is waived if x-rays indicate ossification of the cochlea 
– Post lingual onset of severe or profound hearing loss 
– Limited benefit from appropriately fitted hearing aids defined as scoring 50% or less on a test of open-set sentence recognition (HINT sentences) 
– Little or no benefit from appropriately fitted hearing aids, defined as: 
 • In younger children (<4 years of age): a failure to reach developmentally appropriate milestones (such as spontaneous response to name in quiet or to environmental sounds) measured using the Infant-Toddler Meaningful Auditory Integration Scale or Meaningful Auditory Integration Scale or <20% correct on a simple open-set word recognition test (Multisyllabic Lexical Neighborhood Test) administered using monitored live voice (70 dB SPL) 
 • In older children (≥4 years of age): scoring <12% on a difficult open-set word recognition test (Phonetically Balanced-Kindergarten Test) or <30% on an open-set sentence test (Hearing in Noise Test for Children) administered using recorded materials in the sound field (70 dB SPL) 
Adults Children
– 18 years of age or older  – 12 months through 17 years of age 
– Severe-to-profound, bilateral sensorineural hearing loss (>70 dB HL)  – Profound, bilateral sensorineural deafness (≥90 dB HL) 
– Use of appropriately fitted hearing aids for at least 6 months in children 2 through 17 years of age, or at least 3 months in children 12 through 23 months of age. The minimum duration of hearing aid use is waived if x-rays indicate ossification of the cochlea 
– Post lingual onset of severe or profound hearing loss 
– Limited benefit from appropriately fitted hearing aids defined as scoring 50% or less on a test of open-set sentence recognition (HINT sentences) 
– Little or no benefit from appropriately fitted hearing aids, defined as: 
 • In younger children (<4 years of age): a failure to reach developmentally appropriate milestones (such as spontaneous response to name in quiet or to environmental sounds) measured using the Infant-Toddler Meaningful Auditory Integration Scale or Meaningful Auditory Integration Scale or <20% correct on a simple open-set word recognition test (Multisyllabic Lexical Neighborhood Test) administered using monitored live voice (70 dB SPL) 
 • In older children (≥4 years of age): scoring <12% on a difficult open-set word recognition test (Phonetically Balanced-Kindergarten Test) or <30% on an open-set sentence test (Hearing in Noise Test for Children) administered using recorded materials in the sound field (70 dB SPL) 
TABLE II.

Adult and pediatric cochlear implant candidacy (Cochlear Ltd.).

Adults Children
– Individuals 18 years of age or older who have bilateral, pre, peri, or post-linguistic sensorineural hearing impairment – Limited benefit from appropriate binaural hearing aids, as defined by test scores of 50% correct or less in the ear to be implanted (60% or less in the best-aided condition) on tape-recorded tests of open-set sentence recognition – Moderate-to-profound hearing loss in the low frequencies and profound (>90 dB HL) hearing loss in the mid to high speech frequencies – Individuals 18 years of age or older who have normal hearing in one ear and severe-to-profound sensorineural hearing loss in the contralateral ear with a CNC word score of 5% or poorer  – Children 9 to 24 months who have bilateral, profound sensorineural deafness – Little benefit from appropriate binaural hearing aids as defined as:  • In younger children: lack of progress in the development of simple auditory skills in conjunction with appropriate amplification and participation in intensive aural habilitation over a three-to-six-month period. It is recommended that limited benefit be quantified on a measure such as the Meaningful Auditory Integration Scale or the Early Speech Perception test.  • In older children: ≤30% correct on the open-set Multisyllabic Lexical Neighborhood Test (MLNT) or Lexical Neighborhood Test (LNT), depending upon the child's cognitive and linguistic skills. A three-to-six-month hearing aid trial is recommended for children without previous aided experience. – Children 5 years of age or older who have normal hearing in one ear and severe-to-profound sensorineural hearing loss in the contralateral ear with a CNC word score of 5% or poorer 
Adults Children
– Individuals 18 years of age or older who have bilateral, pre, peri, or post-linguistic sensorineural hearing impairment – Limited benefit from appropriate binaural hearing aids, as defined by test scores of 50% correct or less in the ear to be implanted (60% or less in the best-aided condition) on tape-recorded tests of open-set sentence recognition – Moderate-to-profound hearing loss in the low frequencies and profound (>90 dB HL) hearing loss in the mid to high speech frequencies – Individuals 18 years of age or older who have normal hearing in one ear and severe-to-profound sensorineural hearing loss in the contralateral ear with a CNC word score of 5% or poorer  – Children 9 to 24 months who have bilateral, profound sensorineural deafness – Little benefit from appropriate binaural hearing aids as defined as:  • In younger children: lack of progress in the development of simple auditory skills in conjunction with appropriate amplification and participation in intensive aural habilitation over a three-to-six-month period. It is recommended that limited benefit be quantified on a measure such as the Meaningful Auditory Integration Scale or the Early Speech Perception test.  • In older children: ≤30% correct on the open-set Multisyllabic Lexical Neighborhood Test (MLNT) or Lexical Neighborhood Test (LNT), depending upon the child's cognitive and linguistic skills. A three-to-six-month hearing aid trial is recommended for children without previous aided experience. – Children 5 years of age or older who have normal hearing in one ear and severe-to-profound sensorineural hearing loss in the contralateral ear with a CNC word score of 5% or poorer 
TABLE III.

Adult and pediatric cochlear implant candidacy (Med El).

Adults Children
– 18 years of age or older who have bilateral, sensorineural hearing impairment
– Limited benefit from appropriately fitted binaural hearing aids, defined by test scores of 40% correct or less in the best-aided listening condition on CD recorded tests of open-set sentence recognition (Hearing In Noise Test (HINT) sentences)
– Bilateral severe-to-profound sensorineural hearing loss determined by a pure tone average of 70 dB HL or greater at 500 Hz, 1000 Hz, and 2000 Hz
– Individuals 18 years of age or older who have normal hearing in one ear and profound sensorineural hearing loss in the contralateral ear and a CNC word score of 5% or poorer 
– 12 months of age or older who demonstrate a profound, bilateral sensorineural hearing loss with thresholds of 90 dB or greater at 1000 Hz
– Lack of hearing aid benefit is defined as:
 • In younger children: lack of progress in the development of simple auditory skills in conjunction with appropriate amplification and participation in intensive aural rehabilitation over a three-to-six-month period
 • In older children: ≤20% correct on the MLNT or LNT, depending upon the child's cognitive ability and linguistic skills
– A three-to-six-month hearing aid trial is required for children without previous experience with hearing aids. Radiological evidence of cochlear ossification may justify a shorter trial with amplification
– Children 5 years of age or older who have normal hearing in one ear and profound sensorineural hearing loss in the contralateral ear and a monosyllabic word recognition score of 5% or poorer 
Adults Children
– 18 years of age or older who have bilateral, sensorineural hearing impairment
– Limited benefit from appropriately fitted binaural hearing aids, defined by test scores of 40% correct or less in the best-aided listening condition on CD recorded tests of open-set sentence recognition (Hearing In Noise Test (HINT) sentences)
– Bilateral severe-to-profound sensorineural hearing loss determined by a pure tone average of 70 dB HL or greater at 500 Hz, 1000 Hz, and 2000 Hz
– Individuals 18 years of age or older who have normal hearing in one ear and profound sensorineural hearing loss in the contralateral ear and a CNC word score of 5% or poorer 
– 12 months of age or older who demonstrate a profound, bilateral sensorineural hearing loss with thresholds of 90 dB or greater at 1000 Hz
– Lack of hearing aid benefit is defined as:
 • In younger children: lack of progress in the development of simple auditory skills in conjunction with appropriate amplification and participation in intensive aural rehabilitation over a three-to-six-month period
 • In older children: ≤20% correct on the MLNT or LNT, depending upon the child's cognitive ability and linguistic skills
– A three-to-six-month hearing aid trial is required for children without previous experience with hearing aids. Radiological evidence of cochlear ossification may justify a shorter trial with amplification
– Children 5 years of age or older who have normal hearing in one ear and profound sensorineural hearing loss in the contralateral ear and a monosyllabic word recognition score of 5% or poorer 

Since there is a real risk of surgical complications, the FDA approval process is a lengthy and complex undertaking for an invasive medical device or changes in candidacy and procedures related to its use. Cochlear implants are designated by the FDA as a class III medical device and, as such, are subject to the greatest degree of regulatory scrutiny of the three medical classes. For example, the FDA requires device registration, device listing, proper labeling, and GMP (good manufacturing practice) before a clinical trial can be initiated. This is generally defined as governmental regulation related to compliance with legal quality standards during the manufacture and packaging of health care products for the protection of patients. Clinical experience has demonstrated the FDA processes to be laborious, and lengthy. Although the FDA has a regulatory time requirement in which they must respond to a submission, it is often the case the deadline is extended, making the process extremely time-consuming. In fact, real-world clinical practice may on occasion precede final FDA action. For example, individuals diagnosed with severe-to-profound hearing loss bilaterally and individuals with single-sided deafness were sometimes implanted “off-label” utilizing currently available devices prior to FDA approval for these populations. Despite this complex FDA approval process, the field of cochlear implants has continually evolved in candidacy requirements for the technology, clinical and surgical practices, and processing strategies.

In 1985, when the FDA approved the use of the Nucleus 22 cochlear implant for post-lingually deafened adults (i.e., after the development of language), candidates had to demonstrate profound sensorineural hearing loss bilaterally and show evidence of having no unaided or aided speech perception abilities.3 In 1990, the FDA approved the use of the Nucleus 22 cochlear implant for adults with bilateral profound sensorineural hearing loss who were pre-linguistically or post-linguistically deafened (i.e., before or after the development of language). In 1998, the FDA approved the Nucleus 24M cochlear implant, and candidacy criteria were expanded to include adults with bilateral moderate-to-profound sensorineural hearing loss who demonstrated limited benefit from appropriately fit hearing aids, as defined as scoring 40% or poorer on a recorded open-set sentence test in the best-aided (bilaterally optimized) condition. In 2002, the Nucleus 24 Contour cochlear implant system was approved by the FDA. Criteria were expanded to allow for implantation of adults with bilateral moderate-to-profound sensorineural hearing loss who demonstrated limited benefit from amplification as defined as 60% or poorer in the best- aided condition and 50% or poorer in the ear to be implanted.12 However, adults insured by Medicare were required to perform 40% or poorer in best-aided condition.4,5 Recently, Medicare guidelines changed following the Centers for Medicare and Medicaid Services (CMS) recommendations to change their National Coverage Determination (NCD) to match the indications followed by private insurance companies. In 2014, the FDA approved the use of Cochlear's Hybrid L24 implant, a shortened electrode array specifically designed to preserve low-frequency residual hearing. This device allowed patients to take advantage of electric and acoustic stimulation (EAS) in the same ear provided hearing could be preserved post-implantation.5 In a similar manner, strategies for drugs including biological therapies were also being developed during this time to address multiple levels of hearing preservation. In 2016, Med El received FDA approval for the Med El Synchrony EAS device, which was also designed to preserve low-frequency residual hearing. In 2017 Advanced Bionics released an acoustic ear hook for the Naida Q90 sound processor, which allowed patients with hearing preservation in the low frequencies to capitalize on the benefits of concurrent acoustic stimulation. The approval of these devices has expanded the candidacy criteria for patients with significant residual low-frequency hearing who have a steeply sloping moderate-to-profound hearing loss typically seen in individuals with a significant history of noise exposure and who have not worn adequate hearing protection.

Since 2019, RMEC has conducted over 550 cochlear implant evaluations, and of those evaluated, approximately one-third of these patients have reported a significant history of noise exposure. To date, most patients with this significant history would be ideal candidates for either medical or surgical intervention. Relative to this, there are several emerging biological interventions being evaluated for patients with noise-induced hearing loss.13 The intent of these therapeutics is to partially repair the damage from noise exposure. These strategies will no doubt have an important effect on cochlear implant candidacy. At present, their inclusion criteria for patients to enter regeneration studies overlap with many utilized criteria for cochlear implantation candidacy. For example, in adult patients, these could include severe-to-profound unilateral or bilateral sensorineural hearing loss, hearing loss due to noise exposure or sudden stable sensorineural hearing loss, age-related sensorineural hearing loss, and acquired, non-genetic sensorineural hearing loss of a significant degree. In fact, one drug study in adults requires the subject to meet criteria for cochlear implantation and opt to undergo cochlear implant surgery (National Clinical Trial Number 03300687). Conversely, some drug study inclusion criteria differ from those of cochlear implantation such as a pure tone average of 26–70 dB HL (National Clinical Trial Numbers 04120116, 04462198, 04601909). Regarding pediatric patients, there is an overlap in criteria that includes unilateral or bilateral severe-to-profound acquired sensorineural hearing loss.13 Considering these obvious overlaps, when these drug therapies have been fully studied in terms of toxicity and efficacy, biological interventions will very likely be utilized either prior to or in concert with cochlear implantation.

The candidacy criteria have expanded recently, allowing individuals with normal hearing in one ear, but who experienced severe-to-profound hearing loss in the other, to be treated with this technology. Med El received approval in July 2019, and Cochlear Ltd. received FDA approval in January 2022 for use of cochlear implants in individuals with single-sided deafness.14 As of September 2022, Advanced Bionics has not received FDA approval for expanded indications of single-sided deafness.

In 1990, the FDA approved the use of the Nucleus 22 for children 2 to 17 years of age with bilateral profound sensorineural hearing loss who derived little or no benefit from hearing or vibrotactile aids as demonstrated by the inability to improve on an age-appropriate closed-word identification task. In 1998, candidacy criteria for children were expanded to allow for implantation in the presence of some functional hearing, as defined as having 20% or poorer understanding of words using an open-set test with appropriately fit hearing aids. By early 2000, candidacy criteria were modified further to permit children with profound hearing loss to be implanted at a younger age (12 months of age). In addition, these new criteria allowed children with greater residual hearing (i.e., children with severe-to-profound hearing loss) who demonstrated word understanding of 30% or poorer on an open-set test with an appropriately fit hearing aid to be implanted at 24 months to 17 years of age.5,15 In March of 2020, Cochlear obtained approval from the FDA to lower the age a child with profound bilateral sensorineural hearing loss could receive an implant from 12 months to nine months of age.16 With recent changes in indications allowing implantation for single-sided deafness from two of the three implant manufacturers, children five and older with single-sided deafness can also be treated with cochlear implant technology.14 The changes in adult and pediatric candidacy from 1985 to date can be seen in Table IV.

TABLE IV.

Evolution of candidacy criteria.

  1985  1990  1998  2000–Current 
AGE  Adults  Adults Children (2yrs+)  Adults Children (18 months+)  Adults Children (9 months+) (2020) 
ONSET of Hearing Loss  Post-linguistic  Post-linguistic Adults  Adults and Children  Adults and Children 
Pre and Post-linguistic Children  Pre and Post-linguistic  Pre and Post-linguistic 
DEGREE of SNHL (UNAIDED)  Profound Bilateral Sensorineural Hearing Loss  Profound Bilateral Sensorineural Hearing Loss  Severe-to-Profound Bilateral Sensorineural Hearing Loss Adults  Adults Moderate-to-Profound Bilateral Sensorineural Hearing Loss 
Residual Low-Frequency with Severe-to-Profound High-Frequency Sensorineural Hearing Loss (Hybrid) (2014) 
Infants (9–23 months) Profound (2020) Bilateral Sensorineural Hearing Loss 
Profound Bilateral Sensorineural Hearing Loss Children 
Children (2–17 years) Severe-to-Profound Bilateral Sensorineural Hearing Loss 
Adults and Children (5 years+) Normal hearing in one ear; Severe-to-Profound loss in the opposite ear (2022) 
ADULT Open-set sentences (AIDED)  0%  0%  40% or less  Private Insurance: ≤ 50% sentence recognition in the ear to be implanted and ≤ 60% binaurally aided 
Medicare: 40% best-aided (prior to September 2022) 
Medicare: ≤50% sentence recognition in ear to be implanted and ≤60% binaurally aided (current) 
PEDIATRIC Speech Score (AIDED)  Not candidates  0% open-set  Lack of auditory progress  Infants: No progress in auditory skill development with hearing aids and intervention 
≤ 20% (MLNT/LNT)  Children: ≤ 30% open-set speech recognition (MLNT/LNT) 
  1985  1990  1998  2000–Current 
AGE  Adults  Adults Children (2yrs+)  Adults Children (18 months+)  Adults Children (9 months+) (2020) 
ONSET of Hearing Loss  Post-linguistic  Post-linguistic Adults  Adults and Children  Adults and Children 
Pre and Post-linguistic Children  Pre and Post-linguistic  Pre and Post-linguistic 
DEGREE of SNHL (UNAIDED)  Profound Bilateral Sensorineural Hearing Loss  Profound Bilateral Sensorineural Hearing Loss  Severe-to-Profound Bilateral Sensorineural Hearing Loss Adults  Adults Moderate-to-Profound Bilateral Sensorineural Hearing Loss 
Residual Low-Frequency with Severe-to-Profound High-Frequency Sensorineural Hearing Loss (Hybrid) (2014) 
Infants (9–23 months) Profound (2020) Bilateral Sensorineural Hearing Loss 
Profound Bilateral Sensorineural Hearing Loss Children 
Children (2–17 years) Severe-to-Profound Bilateral Sensorineural Hearing Loss 
Adults and Children (5 years+) Normal hearing in one ear; Severe-to-Profound loss in the opposite ear (2022) 
ADULT Open-set sentences (AIDED)  0%  0%  40% or less  Private Insurance: ≤ 50% sentence recognition in the ear to be implanted and ≤ 60% binaurally aided 
Medicare: 40% best-aided (prior to September 2022) 
Medicare: ≤50% sentence recognition in ear to be implanted and ≤60% binaurally aided (current) 
PEDIATRIC Speech Score (AIDED)  Not candidates  0% open-set  Lack of auditory progress  Infants: No progress in auditory skill development with hearing aids and intervention 
≤ 20% (MLNT/LNT)  Children: ≤ 30% open-set speech recognition (MLNT/LNT) 

In the early years of cochlear implantation, when aided thresholds could not be obtained because of the profound nature of the loss and before MRI was available to verify auditory nerve and internal auditory canal (IAC) structure, a promontory stimulator was used to determine if the patient had an auditory percept. The surgeon anesthetized the eardrum and placed a long needle trans-tympanically on the cochlear promontory. The audiologist delivered electrical current of varying frequencies and intensities through the needle to the promontory noting if the patient was able to perceive an auditory stimulus from the electrical current. If the patient did not report an auditory percept, the patient was not excluded from surgical consideration, but was counseled conservatively regarding expectations post-activation.17 Today, promontory stimulation is used by some clinics to guide decision-making and counseling in off-label cases of cochlear implantation after the treatment of cerebellopontine angle tumors rather than how it was intended to be used early in the history of cochlear implantation. Therefore, as candidacy criteria were expanded to allow for the implantation of individuals with residual hearing, changes in clinical practices were noted.

Particularly relevant to this special issue of JASA, there is a parallel between the evolution of inclusion criteria and primary outcomes for cochlear implants as well as biological drugs that are intended to restore hearing (Table V). However, there are significant differences between these two interventions. For example, devices requiring surgical intervention can have operative and post-operative complications. On the other hand, biological interventions may have more subtle adverse events, both short and long term, that are generally not associated with surgical devices. The evolution of both inclusion criteria and primary outcomes for these interventions have followed a similar path.

TABLE V.

Evolution of candidacy and outcomes for surgical and biological interventions.

Adult evolution of candidacy/outcomes Surgical intervention Biological intervention
Early candidacy criteria  Profound bilateral sensorineural hearing loss with 0% open set sentence test in quiet  Non-fluctuating severe-to-profound unilateral or bilateral hearing loss (NCT02132130) 
Severe-to-profound sensorineural hearing loss of 80 dB HL or poorer at 500 Hz (NCT03300687) 
Early primary outcome  Sound field thresholds  Adverse events, conventional audiometry 
Speech perception results (word and sentences)  Tinnitus, vertigo and perforation 
Most current candidacy criteria  Moderate-to-profound bilateral sensorineural hearing loss with 60% open set sentence test (in noise) in best aided condition and 50% in ear to be implanted  Documented, stable hearing loss and word recognition tests ± 6% (NCT05061758) 
Normal hearing in one ear with severe-to-profound sensorineural hearing loss in contralateral ear  PTA of 35–85 dB HL in ear to be injected (NCT05086276) 
Most current primary outcome  Speech perception results (word and sentences)  Number of responders with at least 2 dB improvement in adaptive sentence test Speech perception results 
Adult evolution of candidacy/outcomes Surgical intervention Biological intervention
Early candidacy criteria  Profound bilateral sensorineural hearing loss with 0% open set sentence test in quiet  Non-fluctuating severe-to-profound unilateral or bilateral hearing loss (NCT02132130) 
Severe-to-profound sensorineural hearing loss of 80 dB HL or poorer at 500 Hz (NCT03300687) 
Early primary outcome  Sound field thresholds  Adverse events, conventional audiometry 
Speech perception results (word and sentences)  Tinnitus, vertigo and perforation 
Most current candidacy criteria  Moderate-to-profound bilateral sensorineural hearing loss with 60% open set sentence test (in noise) in best aided condition and 50% in ear to be implanted  Documented, stable hearing loss and word recognition tests ± 6% (NCT05061758) 
Normal hearing in one ear with severe-to-profound sensorineural hearing loss in contralateral ear  PTA of 35–85 dB HL in ear to be injected (NCT05086276) 
Most current primary outcome  Speech perception results (word and sentences)  Number of responders with at least 2 dB improvement in adaptive sentence test Speech perception results 

Accumulated experience with cochlear implantation and patient outcomes in conjunction with advancements in technology and expansion in cochlear implant candidacy has heavily influenced patient counseling. This has included the possibility of performing poorly with a cochlear implant despite appearing to be an appropriate candidate for implantation. Expectations have significantly changed over time as technology has improved and candidacy criteria have been expanded. In response to this, the counseling process has also evolved, particularly for high-volume clinics with adequate experience with implantation and post-operative follow-up.

Adults and children who met the early cochlear implant criteria of bilateral profound sensorineural hearing loss were unilaterally implanted. Multiple reasons were cited for the inclination to favor unilateral implantation such as a concern of irreversible damage to the cochlea which would prevent access to potential therapeutic measures such as genetic, pharmacologic, and stem cell therapies. Early in cochlear implantation experience, implant recipients frequently did not aid the non-implanted ear following surgery especially when the speech perception score of the contralateral ear was extremely poor. By the late 1990s, as candidacy criteria expanded to allow for the implantation of individuals with more residual hearing, most clinicians encouraged bimodal use; acoustic hearing in one ear and electric hearing in the contralateral ear. Numerous studies demonstrated that significant benefits could be obtained from the continued use of a hearing aid for the contralateral ear for recipients who demonstrated measurable speech perception ability in that ear.18,19 Some of these benefits included improved sound quality, music appreciation and performance in noise.20 By the mid-2000s, the topic of bilateral cochlear implantation was generating increasing interest in the medical community. Many implant clinics, including RMEC, were beginning to offer sequential and simultaneous bilateral cochlear implantation to individuals with bilateral severe-to-profound sensorineural hearing loss. Research into bilateral implantation supported the benefits of bilateral hearing, particularly in noisy environments.21–23 As the benefits of bilateral cochlear implantation were realized and numerous studies were published demonstrating the potential positive clinical results, the practice became more common.24 In 2008, The William House Cochlear Implant Study Group published its position statement indicating bilateral cochlear implantation as the standard of care for adults and children with bilateral severe-to-profound SNHL.25 

The surgical technique of cochlear implantation has evolved with the changing implant criteria. Surgical techniques were not focused on hearing preservation in the early years of cochlear implantation as candidates did not have any serviceable hearing. As candidacy guidelines expanded to allow for the implantation of recipients with residual hearing, it was discovered that after implanting these individuals, some recipients maintained sensorineural hearing despite the presence of an implant.26 This sparked a line of investigation into hearing preservation in cochlear implantation, similar to the scrutiny of hearing preservation in noise-induced hearing disorders. For example, there is intense interest in pharmaceutical interventions and hearing regeneration. The success of these efforts will have significant implications for the future utilization of cochlear implantation.

Whether relevant to devices or drugs, research into the phenomenon of hearing preservation despite introducing a foreign body into the inner ear has resulted in changes in surgical technique and the development of specialized electrodes. Temporal bone studies of implantation revealed the different mechanisms of trauma to the delicate structures within the cochlea. With the identification of these mechanisms, electrode arrays were designed to minimize trauma to the cochlea.27 

In October 2000, the Nucleus 24 Contour device which incorporated features to minimize trauma including a downsized, thinner receiver-stimulator and a perimodiolar electrode array, received FDA approval.12 One of the objectives of the Nucleus 24 Contour Clinical Trial was to assess hearing preservation with a less traumatic electrode array. Postoperative thresholds in the implanted ear were assessed for subjects who had measurable hearing pre-operatively. Results from the Contour Clinical Trial indicated that 46% of patients with pre-operative residual hearing retained some level of unaided hearing following surgery, supporting the atraumatic properties of the Nucleus 24 Contour device.12 In 2009, the FDA approved the use of the CI512 device, which utilized an even thinner, lower profile receiver-stimulator, negating the need for drilling a seat on the parietal aspect of the calvarium, which can potentially cause additional noise-induced hearing loss. With a thin profile, the receiver-stimulator could be positioned into a tight sub-periosteal pocket rather than requiring drilling of a well or ramped seat.3 In 2014 the FDA approved the use of the Nucleus Hybrid System (L24), which is a thinner and shorter 16 mm straight electrode array with 22 half-banded contacts designed to preserve the apical structures of the cochlea responsible for low-frequency hearing. Results from the clinical trials of the hybrid implant system indicated that at six months post-surgery, 66% of subjects maintained functional hearing.28 Additionally, subjects with aidable, residual hearing performed better than those who lost functional residual hearing. However, subjects who lost their residual, aidable hearing following surgery performed significantly better compared to their aided preoperative performance.28 Similarly, in 2016 the FDA approved the use of the Med El Synchrony EAS device, which was also designed to preserve low-frequency residual hearing. Several studies have demonstrated the improved performance seen when a patient utilizes both electrical hearing (through the cochlear implant) and acoustic hearing (through hearing aid stimulation of residual low-frequency hearing) in the same ear.29,30

With the introduction of more delicate electrodes, minimally invasive cochlear implantation techniques have been investigated to further refine techniques for native hearing preservation. Techniques have been investigated such as a round window approach rather than a cochleostomy, negating the need for drilling away bone to access the scala tympani. Additional hearing-preservation surgical techniques have included developing atraumatic electrode insertion maneuvers such as robotic-assisted insertion of electrodes, inserting the electrode at slower speeds, using slower drill speeds, and performing the implantation with the middle ear filled with different types of solution to minimize intralabyrinthine perilymph volume changes. Intraoperative steroids were also introduced to improve hearing preservation outcomes22 and are analogous to potential pharmaceuticals as therapeutic interventions designed to improve hearing preservation for noise-induced hearing loss. Different steroid protocols have been developed by individual surgeons and implant centers with the goal to minimize trauma to native hearing structures. Steroid protocols have included preoperative and postoperative oral steroids, intravenous steroids administered at the time of surgery, and the use of steroid-containing solutions instilled into the middle ear during electrode insertion. The idea of a steroid eluting electrode has been under consideration for many years. The first trial of such an electrode is currently in progress to study the effects of the electrode on measures that may help infer the injury sustained within the cochlea on implantation. A multi-center, double blinded, global clinical study is currently evaluating the efficacy of a dexamethasone eluting electrode in the reduction of fibrosis in an adult population with bilateral moderate-to-profound sensorineural hearing loss. If successful, candidacy protocols for cochlear implantation might be expanded to account for the adjunctive effectiveness of the pharmaceutical intervention.

Speech coding strategies have evolved considerably from the earliest cochlear implants. The speech coding strategy that was utilized in the earliest devices was much less sophisticated than those that exist today. For instance, the earliest speech coding strategies used feature extraction to represent F0 by the stim rate and the addition of F2 or F1+F2. F0/F2 was the first strategy used in the earliest U.S. clinical trials. When the Nucleus 22 came to market in the mid-1980s, a formant (F0, F1, F2) strategy was employed by Cochlear Ltd.31,32 In this strategy, the fundamental frequency (F0) and subsequent formants were extracted from the speech signal using zero crossing detectors. The zero-crossing detectors were used to estimate defined formant frequency bands (F0 < 270 Hz, F1 280–1000 Hz, F2 1000–4000 Hz). The amplitude of the formant band was estimated with an envelope detector by rectifying and low pass filtering and then presenting on a designated electrode.

The formant strategy was later replaced by a MPEAK strategy (feature extraction and spectral coding). In the MPEAK strategy, both formant information and high-frequency information were extracted. With the addition of the high-frequency information, consonant identification improved significantly.31 The development of the continuous interleaved sampling (CIS) strategy, which utilized biphasic electrical stimulation delivered sequentially to typically eight electrodes that best corresponded with the frequencies most salient in the amplitude envelope of the original signal33 led to improvements in speech recognition. In a SPEAK strategy (spectral coding strategy), which was similar to a CIS strategy, the incoming signal was sent to a bank of 20 filters with center frequencies ranging from 250 Hz to 10 kHz. The SPEAK processor continuously estimated the outputs of the 20 filters and selected the filters with the largest amplitudes. The number of maxima selected varied from five to ten depending on the spectral composition of the input signal, with an average number of six maxima. The electrical current was then delivered at 250 pulses per second.32,34,35

SPEAK was eventually replaced by an advanced combination encoder (ACE) strategy. The ACE strategy utilized a combination of both place and rate strategies. It used a roving pattern of stimulation with the flexibility of selecting between one to 20 maxima.35 In this strategy, there was a choice of the stimulation rate between 250 to 2400 Hz per channel. Additional studies were conducted to analyze the impact of various rates of stimulation on speech perception scores. A randomized, prospective, single-blind study using a within-subject design at 14 academic centers, including RMEC, concluded there was no advantage to the utilization of higher stimulation rates, although subjects preferred slower rates. Subjects performed well regardless of stimulation rate, scoring approximately 57% on a CNC word task and 78% on the hearing in noise test (HINT) in quiet.36 

Similarly, the strategies of Advanced Bionics and Med El for encoding speech evolved over time. One of earliest speech coding strategies of Advanced Bionics included the simultaneous analog strategy (sas) that provided stimulation of simultaneous electrical waveforms on multiple electrodes. The sas strategy was able to maintain the salient acoustic cues from the original speech signal but created significant demands from the battery of the processor as well as cross-channel interaction for some recipients. Later strategies employed biphasic electrical stimulation which avoided the cross-channel interaction of sas. Multiple pulsatile sampler (MPS) was a variation of a CIS strategy that provided a partially simultaneous stimulation strategy but was once again found to cause cross-channel interaction for some recipients. Eventually, more sophisticated strategies such as HiResolution (HiRes), a variation of CIS, were made commercially available. HiRes allowed for the stimulation of 16 electrodes, a higher stimulation rate and higher cutoff frequencies than what had been available previously. Two variations of HiRes were introduced: HiRes Single, which provided sequential stimulation, and HiRes Paired, which provided a partially simultaneous stimulation option. In 2006, HiRes Fidelity 120 was introduced, which allowed for intentional current steering to create virtual channels.37 HiRes Fidelity 120 was later replaced by HiRes Optima (single and paired), with the primary intention of optimizing battery consumption of the processor.

Med El has released variations of CIS, most notably CIS+ and high-definition CIS (HDCIS). The CIS+ strategy was like traditional CIS strategies but utilized a Hilbert transformation rather than wave rectification to capture the speech signal. The HDCIS strategy also utilized a Hilbert transformation as well as a wider frequency range and higher stimulation rate than previous strategies. Overlapping filter banks were a by-product of the Hilbert transformation and subsequently allowed for the perception of intermediate pitch percepts. The fine structure processing (FSP) strategy was later released, which was akin to CIS+ and HDCIS, except it altered the timing of pulse bursts in the apical end of the electrode array depending on the input frequency of the original signal. The FSP strategy offered two variations, FS4 and FS4-p, both of which provided modulations to stimulation of electrodes in the apical end of the electrode array.34 As this is a brief summary of the evolution of the processing strategy, other authors have provided a further detailed overview of the historical development of the speech processing strategies of all three FDA-approved cochlear implant manufacturers.34,35

Manufacturers often receive FDA approval for a speech coding strategy intended to be used with a specific population. However, clinicians may decide to use that strategy with other recipients if the speech perception performance is believed to be better when using that strategy. For example, Advanced Bionics received FDA approval for HiRes following a clinical trial that demonstrated better speech recognition scores amongst adults who were given the HiRes strategy compared to more traditional strategies.38 The trial was conducted with adults but clinically it is used routinely for both adults and children, even though the FDA trial was not conducted with a pediatric population.

RMEC has participated in most of the clinical trials reported in this article and its experience in research has influenced the candidacy and outcome assessment protocols its team has established as shown in Tables VI–X. Although a standardized outcome assessment protocol for assessing adults and children has been adopted, the members of the implant team periodically revisit this protocol to determine if changes need to be made. The implant center has an installment base of over 3500 patients and has been tracking pre-operative and post-operative test results for over 30 years. With such a large database, the clinic has been able to establish its own clinical normative data. This has been beneficial during the candidacy process when counseling candidates about what to expect post-operatively. It has allowed the center to create benchmarks for how patients typically perform at 3, 6, and 12 months post-operatively, in quiet and in noise.39 Tracking speech perception scores allows clinicians to identify changes in individual performance over time. Monitoring outcomes also allows for detection of trends in the data set (e.g., do certain etiologies perform better than others?). In addition, sharing data with other experienced implant centers creates an even larger “big data set.”39 National registries make it possible to follow trends in performance and hearing preservation rates among not only cochlear implant recipients but could also be employed for individuals with noise-induced hearing disorders. This perceived need supports the importance of the current emergence of biological agents designed for hearing regeneration. Comparison of local clinical data sets with published clinical trial outcomes is also possible. For example, the Freedom clinical trials and n5 clinical trials from cochlear show that recipients score approximately 60% on recorded CNC words36,40 and RMEC's recipients score 64% on recorded CNC words, demonstrating good agreement with previously published data.

TABLE VI.

Adult cochlear implant candidacy protocol.

Hearing testing/Unaided  • Unaided air and bone conduction testing 
• Word recognition testing right and left ear independently 
Verification  • Real Ear testing/ Verifit 
Aided speech perception testing/Auditory only  • CNC 
 ○ In quiet: aided right and left independently (50 words) (60 dBA) 
• Az Bio 
 ○ In quiet: aided right and left independently (20 sentences) (60 dBA) 
 ○ In noise: aided right and left independently (20 sentences) (65 dBA + 5 dB SNR) at 0º Azimuth 
 ○ In noise: aided bilaterally (20 sentences) (65 dBA + 5 dB SNR) at 0º Azimuth 
Validation  • Administer MoCA if patient is over 70 
• Administer SSQ-12 
Hearing testing/Unaided  • Unaided air and bone conduction testing 
• Word recognition testing right and left ear independently 
Verification  • Real Ear testing/ Verifit 
Aided speech perception testing/Auditory only  • CNC 
 ○ In quiet: aided right and left independently (50 words) (60 dBA) 
• Az Bio 
 ○ In quiet: aided right and left independently (20 sentences) (60 dBA) 
 ○ In noise: aided right and left independently (20 sentences) (65 dBA + 5 dB SNR) at 0º Azimuth 
 ○ In noise: aided bilaterally (20 sentences) (65 dBA + 5 dB SNR) at 0º Azimuth 
Validation  • Administer MoCA if patient is over 70 
• Administer SSQ-12 
TABLE VII.

Pediatric cochlear implant candidacy protocol.

Test protocol Older pediatrics (5 and older) Younger pediatrics (under 5)
Hearing testing/Unaided  • Unaided air and bone conduction testing right and left ear independently  • Behavioral responses in sound field (unaided and aided), ear specific if possible 
• Word recognition testing right and left ear independently  • ABR/OAE test results reviewed 
• Survey/ interview parents (IT-MAIS/MAIS) 
• Greater reliance on input from SLP and early interventionists 
Verification  • Real ear testing/ Verifit  • Real ear testing/ Verifit with RECD 
Aided speech perception testing /Auditory Only  • CNC  • Aided speech perception depends on child's abilities 
 ○ Aided right and left independently (at 50 and 60 dBA)—quiet 
 ○ Aided bilateral—quiet 
• Aided BKB-SIN bilaterally at 65 dBA at 0 degrees Azimuth 
Test protocol Older pediatrics (5 and older) Younger pediatrics (under 5)
Hearing testing/Unaided  • Unaided air and bone conduction testing right and left ear independently  • Behavioral responses in sound field (unaided and aided), ear specific if possible 
• Word recognition testing right and left ear independently  • ABR/OAE test results reviewed 
• Survey/ interview parents (IT-MAIS/MAIS) 
• Greater reliance on input from SLP and early interventionists 
Verification  • Real ear testing/ Verifit  • Real ear testing/ Verifit with RECD 
Aided speech perception testing /Auditory Only  • CNC  • Aided speech perception depends on child's abilities 
 ○ Aided right and left independently (at 50 and 60 dBA)—quiet 
 ○ Aided bilateral—quiet 
• Aided BKB-SIN bilaterally at 65 dBA at 0 degrees Azimuth 
TABLE VIII.

Hybrid/EAS candidacy and outcome assessment protocol.

Test protocol hybrid/EAS Adults Pediatrics (5–17 years of age)
Hearing testing (Unaided)  • Unaided air and bone conduction testing (fit patient with acoustic component post-operative if aided threshold at 500 Hz ≤70 dB HL)  • Unaided air and bone conduction testing (fit patient with acoustic component post-operative if aided threshold at 500 Hz ≤ 70 dB HL) 
• Test thresholds every visit post-operative to monitor changes in thresholds  • Test thresholds every visit post-operative to monitor changes in thresholds 
• Recorded monosyllabic words (CNCs) each ear pre-operative in quiet 
• Recorded monosyllabic words (WIPI, PBKs or CNCs) depending on child's ability each ear pre-operative in quiet 
Verification  • Rea Ear testing/ Verifit (pre-and post-operative)  • Real Ear testing/ Verifit with RECD (pre-and post-operative) 
Aided speech perception testing /Auditory Only  • CNC  ○ Aided right and left independently (60 dBA) in quiet pre-operative  ○ Implanted ears (bilateral) or implanted ear and aided ear (bimodal) (60 dBA) in quiet post-operative • Aided Az Bios (65 dBA + 5 dB SNR) at 0º azimuth bilaterally and ear to be implanted pre-operative • Az Bios (65 dBA + 5 dB SNR) at 0º azimuth with two implants or bimodal condition post-operative  • Monosyllabic words (see above, test depends on child's abilities)  ○ Aided right and left independently and bilaterally (60 dBA) in quiet pre-operative  ○ Implanted ears (bilateral) or implanted ear and aided ear (bimodal) (60 dBA) in quiet post-operative • Aided BKB-SIN bilaterally (65 dBA) at 0º azimuth bilaterally and ear to be implanted pre-operative • BKB-SIN (65 dBA) with two implants or bimodal condition post-operative at 0º azimuth 
Test protocol hybrid/EAS Adults Pediatrics (5–17 years of age)
Hearing testing (Unaided)  • Unaided air and bone conduction testing (fit patient with acoustic component post-operative if aided threshold at 500 Hz ≤70 dB HL)  • Unaided air and bone conduction testing (fit patient with acoustic component post-operative if aided threshold at 500 Hz ≤ 70 dB HL) 
• Test thresholds every visit post-operative to monitor changes in thresholds  • Test thresholds every visit post-operative to monitor changes in thresholds 
• Recorded monosyllabic words (CNCs) each ear pre-operative in quiet 
• Recorded monosyllabic words (WIPI, PBKs or CNCs) depending on child's ability each ear pre-operative in quiet 
Verification  • Rea Ear testing/ Verifit (pre-and post-operative)  • Real Ear testing/ Verifit with RECD (pre-and post-operative) 
Aided speech perception testing /Auditory Only  • CNC  ○ Aided right and left independently (60 dBA) in quiet pre-operative  ○ Implanted ears (bilateral) or implanted ear and aided ear (bimodal) (60 dBA) in quiet post-operative • Aided Az Bios (65 dBA + 5 dB SNR) at 0º azimuth bilaterally and ear to be implanted pre-operative • Az Bios (65 dBA + 5 dB SNR) at 0º azimuth with two implants or bimodal condition post-operative  • Monosyllabic words (see above, test depends on child's abilities)  ○ Aided right and left independently and bilaterally (60 dBA) in quiet pre-operative  ○ Implanted ears (bilateral) or implanted ear and aided ear (bimodal) (60 dBA) in quiet post-operative • Aided BKB-SIN bilaterally (65 dBA) at 0º azimuth bilaterally and ear to be implanted pre-operative • BKB-SIN (65 dBA) with two implants or bimodal condition post-operative at 0º azimuth 
TABLE IX.

Single-sided deafness candidacy and outcome assessment protocol.

Test protocol single-sided deafness Adults Pediatrics (5–17 years of age)
Hearing testing (Unaided)  • Unaided air and bone conduction testing right and left ear independently  • Unaided air and bone conduction testing right and left ear independently 
• Recorded monosyllabic words (CNCs) right and left ear independently  • Recorded monosyllabic words (WIPI, PBKs or CNCs) depending on child's ability right and left ear independently 
Aided speech perception testing  • CNC  • Monosyllabic words (see above, test depends on child's abilities) 
 ○ Aided SSD ear (60 dBA) in sound field masking normal ear pre-operatively  ○ With CI post-operative (60 dBA) in sound field masking normal ear • Aided or in everyday listening condition BKB-SIN (65 dBA) in sound field (speech to front; noise to normal ear) pre-operative • BKB-SIN (65 dBA) in sound field (speech to front; noise to normal ear) with and without CI post-operative • Aided Az Bios (everyday listening condition) (65 dBA + 5 dB SNR) in sound field (speech to front; noise to normal ear) pre-operative • Az Bios (65 dBA + 5 dB SNR) in sound field (speech to front noise to normal ear) with and without CI post-operative 
 ○ Aided SSD ear (60 dBA) in sound field masking normal ear pre-operative  ○ With CI post-operative (60 dBA) in sound field masking normal ear • Aided or in everyday listening condition BKB-SIN (65 dBA) in sound field (speech to front; noise to normal ear) pre-operative • BKB-SIN (65 dBA) in sound field (speech to front; noise to normal ear) with and without CI post-operative 
Test protocol single-sided deafness Adults Pediatrics (5–17 years of age)
Hearing testing (Unaided)  • Unaided air and bone conduction testing right and left ear independently  • Unaided air and bone conduction testing right and left ear independently 
• Recorded monosyllabic words (CNCs) right and left ear independently  • Recorded monosyllabic words (WIPI, PBKs or CNCs) depending on child's ability right and left ear independently 
Aided speech perception testing  • CNC  • Monosyllabic words (see above, test depends on child's abilities) 
 ○ Aided SSD ear (60 dBA) in sound field masking normal ear pre-operatively  ○ With CI post-operative (60 dBA) in sound field masking normal ear • Aided or in everyday listening condition BKB-SIN (65 dBA) in sound field (speech to front; noise to normal ear) pre-operative • BKB-SIN (65 dBA) in sound field (speech to front; noise to normal ear) with and without CI post-operative • Aided Az Bios (everyday listening condition) (65 dBA + 5 dB SNR) in sound field (speech to front; noise to normal ear) pre-operative • Az Bios (65 dBA + 5 dB SNR) in sound field (speech to front noise to normal ear) with and without CI post-operative 
 ○ Aided SSD ear (60 dBA) in sound field masking normal ear pre-operative  ○ With CI post-operative (60 dBA) in sound field masking normal ear • Aided or in everyday listening condition BKB-SIN (65 dBA) in sound field (speech to front; noise to normal ear) pre-operative • BKB-SIN (65 dBA) in sound field (speech to front; noise to normal ear) with and without CI post-operative 
TABLE X.

Outcome assessment protocols (1, 3, 6, and annual visits) for traditional recipients.

Adults Children
• Sound field thresholds • Speech perception in quiet (60 dBA)  ○ CNC words in quiet (implanted ear(s))  ○ AzBio sentences in quiet (implanted ear(s)) • Speech perception in noise (65 dBA + 5 dB SNR) (6 months post-operative) implanted ear and/or when patient is being evaluated for sequential bilateral) at 0º azimuth • SSQ-12 administered at 3 months and annual visits.  • Sound field thresholds • Speech perception in quiet (60 dBA)  ○ CNC words in quiet [implanted ear(s)]  ○ MLNT/LNT/PBK/WIPI may be administered when appropriate rather than CNC • BKB-SIN in noise (implanted ear(s) and/or bimodal condition (65 dBA) (at 6 months post-operative; annual post-operative visits or when patient is being evaluated for sequential bilateral) at 0º azimuth • Children that are unable to perform speech perception testing are given parent surveys (IT-MAIS/MAIS) to assess outcomes 
Adults Children
• Sound field thresholds • Speech perception in quiet (60 dBA)  ○ CNC words in quiet (implanted ear(s))  ○ AzBio sentences in quiet (implanted ear(s)) • Speech perception in noise (65 dBA + 5 dB SNR) (6 months post-operative) implanted ear and/or when patient is being evaluated for sequential bilateral) at 0º azimuth • SSQ-12 administered at 3 months and annual visits.  • Sound field thresholds • Speech perception in quiet (60 dBA)  ○ CNC words in quiet [implanted ear(s)]  ○ MLNT/LNT/PBK/WIPI may be administered when appropriate rather than CNC • BKB-SIN in noise (implanted ear(s) and/or bimodal condition (65 dBA) (at 6 months post-operative; annual post-operative visits or when patient is being evaluated for sequential bilateral) at 0º azimuth • Children that are unable to perform speech perception testing are given parent surveys (IT-MAIS/MAIS) to assess outcomes 

Although there is a standardized candidacy protocol for assessing adults and children, there are cases where cochlear implantation is considered for off-label use. For instance, cochlear implants are found to be beneficial for suppressing the distressing tinnitus accompanying profound idiopathic sudden sensorineural hearing loss.41 In treating individuals off-label with the cochlear implant, additional benefits were noted including improved sound localization and improved hearing in noise. This off-label use led to the FDA IDE studies of cochlear implantation for single-sided deafness.7 As a result, the FDA approved the Med El and Cochlear Ltd. systems for implantation in this condition.

The currently established candidacy protocols at RMEC for adult and pediatric patients can be seen in Tables VI and VII. The adult candidate with bilateral moderate-to-profound sensorineural hearing loss is evaluated in the sound field at 60 dBA with CNC words for the right and left aided conditions. For both test conditions, a 50-word list is administered in the sound field. Additionally, the patient is assessed using AzBio sentences in the right, left and binaurally aided conditions (in quiet and noise). Sentence testing in noise is administered using a +5 dB signal-to-noise ratio presented at 0º Azimuth.42 Modifications to the candidacy and outcome assessment protocols are made when working with individuals who have developmental delays, are non-English speaking or non-verbal. Moreover, RMEC has separate candidacy and outcome assessment protocols for assessing adults and children with considerable low-frequency residual hearing (EAS candidates) and single-sided deafness (Tables VIII and IX).

Subjective testing is equally critical. Since testing in noise can be difficult for many candidates and floor effects are often noted, a quality-of-life measure is obtained pre-operatively. The Speech, Spatial, and Qualities 12 (SSQ-12), which is a shorter version of the Speech, Spatial, and Qualities Questionnaire, consists of 12 questions regarding self-perceived hearing disability across three domains: speech, spatial, and quality. The responses from this survey can give the clinician a deeper insight into how patients perceive their real-world hearing experience, not only for unilateral recipients, but those with bilateral cochlear implants, single-sided deafness, bimodal configurations and hybrid devices. For patients over the age of 70, and for patients who indicate they are experiencing cognitive decline, the Montreal Cognitive Assessment (MoCA) is also administered to obtain a baseline measurement of cognitive status and aid in determining candidacy.43 Recently, the HI-MoCA, a hearing-impaired version of the MoCA has been administered to patients over the age of 70.44 Subjective surveys such as the SSQ-12 and cognitive screening tools may also prove to be helpful tools when assessing individuals with noise-induced and ototoxic hearing losses.

Post-operatively, all patients, regardless of the severity of hearing loss and age at implant are evaluated at activation and at 3-, 6-, and 12-months post-activation, and yearly after their 12-month interval, unless lost to follow-up (Table X). At activation, the patient's unaided audiogram is obtained for the implanted ear. Audiometric thresholds are needed to determine if an acoustic component should be fit, allowing the patient both electric and acoustic stimulation in the implanted ear. An acoustic component is routinely fit if the patient's unaided threshold at 500 Hz is 70 dB HL or better. Verification of the acoustic component is determined using Real Ear Measures. Air and bone conduction testing is conducted at the same frequencies as tested pre-operatively. Comparable speech perception materials are used post-operatively as used pre-operatively. Multiple CNC word and AzBio sentence lists are available, minimizing the possibility of a bias from learning effects.

Patients are assessed with CNC words and AzBio sentences in quiet at three months. Since most patients show ceiling effects on AzBio sentences in quiet, this speech perception measure is not routinely done at subsequent visits the first year. Performance with the implant is typically stable at three to six months post-activation. At six months post-activation, a CNC word score is obtained for the implanted ear. AzBio sentences in noise are also administered in the same condition, but since the signal-to-noise ratio is relatively aggressive (+5 dB), patients continue to demonstrate difficulty with this task. The scores obtained on such a complex sentence test with significant noise can sometimes reflect the central processing function of the patients, and not as accurately capture the patient's peripheral listening ability.45 There is also great variability in terms of scores for AzBio sentences in noise. In a published multicenter study, a within-subject comparison showed that only 52% of subjects showed an improvement at six months post-activation using a +5 dB SNR while 93% of subjects demonstrated a significant improvement on CNC words in the CI-alone condition.46 Instead of administering AzBio sentences in noise, at 3 months post-activation and annually thereafter, the SSQ-12 is administered. Most patients show a significant improvement in their SSQ-12 score, even when their AzBio sentence scores in noise (+5 dB) have not significantly improved. Subsequent testing at 12 months and yearly thereafter consists of CNC word testing and AzBio sentence testing in quiet and administering of the SSQ-12. Currently, the SSQ-12 is the only questionnaire administered pre- and post-operatively to examine hearing scale measures related to quality-of-life. RMEC recognizes that other subjective measures exist, such as the Cochlear Implant Quality-of-Life (CIQOL),47 that could be incorporated into future candidacy and outcome assessment protocols and might also provide additional insights for ototoxic and noise-induced hearing disorders.

During the COVID-19 pandemic, changes in RMEC's post-operative outcome assessment protocols were necessary to reduce the time the patient spent in the clinic. The CNC word test was deemed to be the most appropriate metric for assessing post-operative progress with the device since it is more sensitive to assessing peripheral ability.45,46 Therefore, CNC words were frequently the only metric administered post-operatively, especially in the early months of the pandemic. Additionally, many patients had their programming done remotely, and in those cases, speech perception testing could not be obtained.

The candidacy and outcome assessment protocols followed by clinics across the country today are different from those that existed in the formative years of this technology and vary from clinic to clinic. Currently, if clinicians follow Cochlear's indications, which are generally the least restrictive amongst the FDA-approved devices, adult and pediatric candidates can present with significantly more residual hearing and still qualify for cochlear implantation. For example, adults with private insurance and Medicare are currently considered appropriate cochlear implant candidates if they have bilateral moderate-to-profound hearing loss and sentence understanding of 60% or poorer in the best-aided condition and 50% or poorer in the ear to be implanted. As mentioned previously, Medicare has recently changed its National Coverage Determination (NCD) to match the indications followed by private insurance companies. HINT sentences, which used to be presented in quiet48,49 have been replaced by less contextual sentences, AzBio sentences, which are presented in noise to determine candidacy.50 If clinicians follow Cochlear indications, which are the least restrictive amongst the devices for pediatric populations, the minimum age at implantation has been lowered over time from 2 years to 18 months, to 12 months, to currently 9 months of age if the child has profound sensorineural hearing loss bilaterally. Children two years of age or older with severe-to-profound hearing loss and word understanding of 30% or poorer are deemed implant candidates.5 However, children may receive an implant with greater word recognition than 30% (technically an “off-label” indication) and demonstrate a significant benefit with the use of a cochlear implant.

In the current environment, both cochlear implants and the newer biological therapies have been cited as promising potential treatment options for patients (adult and pediatric) with single-sided deafness or asymmetrical hearing loss.6,7,13 Bilateral implantation or bimodal hearing (implant plus contralateral hearing aid) as well as molecular regeneration therapy have obtained clinical status for patients with bilateral moderate-to-profound sensorineural hearing loss.13,25,51 Surgical techniques and electrode arrays have changed to promote the preservation of residual hearing. All three implant manufacturers offer an EAS option with some processors, acknowledging the benefit of natural acoustic hearing in combination with electric hearing.

The candidacy and outcome assessment protocol most used with adult patients is the Minimum Speech Test Battery (MSTB). Established in 1996 and revised in 2011, the MSTB currently includes the AzBio sentence test and the Consonant-Nucleus-Consonant (CNC) word test.48,49 In 2011, AzBio sentence testing was added to the MSTB with the purpose of providing clinicians with speech perception material having an equivalent level of difficulty across lists.50 Since both medicare and private insurance companies base adult candidacy on sentence scores, many clinics focus on these to determine candidacy and favor the administration of sentences in noise to reflect the listening difficulty of a real-world environment.24 Although the MSTB recommends the use of a +5- and +10-dB signal-to-noise ratio (SNR), each clinic determines how much noise to include in the candidacy and outcome assessment protocols and, therefore, a standard protocol currently does not exist.45 There is also variability in terms of which metrics are included. For example, some clinics only administer sentence tasks and do not obtain aided recorded monosyllabic word scores (CNCs) that are ear specific. Variability in candidacy and outcome assessment protocols may exist in part because implant teams streamline testing to the most clinically relevant measures that are reasonable given the realities of their clinical workflow. It should be noted that in 2017, the Pediatric Minimum Speech Test Battery was published after five years of collaborative input from pediatric clinicians. The intention of this test battery was to create a more standardized candidacy and outcome assessment protocol for children and to define benchmarks for pediatric populations.52 

The Institute for Cochlear Implant Training is in the process of updating candidacy and outcome assessment protocols and has tasked cochlear implant experts with redefining a current MSTB. Having a consistent and comprehensive approach is critical when determining candidacy and the efficacy of treatment. This is particularly relevant not only for cochlear implantation but also for pharmaceutical interventions for noise-induced hearing loss. As delineated above (Table V), it becomes evident that benefits of a biological drug have evolved in a similar manner to the benefits seen with surgical devices.

Regarding surgical devices, there are many practices and assertions in which clinics find agreement. In 2019 a Delphi consensus panel of 30 international specialists voted on statements about cochlear implant use.53 The statements were based on a comprehensive and systematic review of peer-reviewed literature as well as clinical expertise. The panel discussion and subsequent vote resulted in 20 evidence-based consensus statements. The third consensus statement noted that “preferred aided speech recognition tests for cochlear implant candidacy in adults include monosyllabic word tests and sentence tests, conducted in quiet and noise.” The panel added that “further standardization of speech recognition tests is needed to facilitate comparison of outcomes across studies and countries.”53 This statement would support the idea that there is a consensus among experts on the test materials and conditions that should be included to determine cochlear implant candidacy. Additionally, the eighth consensus statement noted that “both word and sentence testing should be used to evaluate speech recognition performance following cochlear implantation.”53 Not only are consistent and standardized protocols essential to determine appropriate candidacy selection but outcome assessment protocols are also critical for tracking individual performance over time and creating industry benchmarks. The utilization of a questionnaire such as the SSQ 12 or a quality-of-life questionnaire in addition to audiometric testing can allow clinicians to further gauge the benefit of a cochlear implant for an individual recipient. The ninth consensus statement supports the use of such questionnaires in the candidacy and outcome assessment protocols.

The evolution of clinical protocols used in the cochlear implant industry to assess candidacy and outcomes parallel the evolving protocols developed to monitor hearing loss for individuals exposed to noise and ototoxic medications. Hearing preservation is an important issue to cochlear implant candidates who often express a concern about losing residual hearing post-operatively. Audiometric threshold testing was incorporated into the outcome assessment protocols years ago when it became known that hearing preservation was possible following cochlear implantation. Additionally, this metric was important in determining whether a recipient would benefit from electro-acoustic stimulation in tandem with electric stimulation. Currently, hearing preservation has become a critical issue for several other medical specialties such as oncology and infectious disease. It is also at the forefront of priorities for the military and organizations such as the Occupational Safety and Health Administration and National Institute for Occupational Safety and Health as it pertains to noise-induced hearing loss. Toxic exposures for individuals who work in contaminated environments can impact the central nervous system, of which hearing is a part. The evolution of outcome assessment protocols for not only surgical interventions but also biological treatments have evolved significantly over time and continue to progress with the advent of new technologies and discoveries.

In summary, there have been numerous changes to cochlear implant candidacy over the last three and a half decades allowing for the implantation of children and adults with significant residual hearing. The evolving regulatory process and changes in clinical care have made it necessary to revisit candidacy and outcome assessment protocols for surgical and biological interventions. Over the past 36 years, participation in national trials and extensive clinical experience with resultant protocol refinement has paralleled the evolution of hearing preservation drug therapies and was critical for proper candidate selection as well as determination of cochlear implantation efficacy.

1.
T.
Lenarz
, “
Cochlear implant—State of the art
,”
GMS Curr. Top. Otorhinolaryngol. Head Neck Surg.
16
,
4
(
2018
).
2.
A. A.
Eshraghi
,
R.
Nazarian
,
F. F.
Telischi
,
S. M.
Rajguru
,
E.
Truy
, and
C.
Gupta
, “
The cochlear implant: Historical aspects and future prospects
,”
Anat. Rec.
295
(
11
),
1967
1980
(
2012
).
3.
A.
Biever
,
J.
Gilden
,
T.
Zwolen
, and
M.
Mears
, “
Upgrade to Nucleus 6 in previous generation cochlear sound processor recipients
,”
J. Am. Acad. Audiol.
29
,
802
813
(
2018
).
4.
Centers for Medicare and Medicaid Services
,
Cochlear Implantation
, http://www.cms.gov/medicare-coverage-database (Last viewed December 16,
2019
).
5.
V.
Nardaran
,
S.
Sydlowski
, and
M.
Li
, “
Evolving criteria for adult and pediatric cochlear implantation
,”
Ear Nose Throat J.
100
(
1
),
31
37
(
2021
).
6.
K.
Brown
,
M.
Dillon
, and
L.
Park
, “
Benefits of cochlear implantation in childhood unilateral hearing loss
,”
Laryngoscope
132
(
56
),
S1
S18
(
2021
).
7.
J.
Galvin
,
Q.
Fu
,
E.
Wilkinson
,
D.
Mills
,
S.
Hagan
,
J.
Lupo
,
M.
Padilla
, and
R.
Shannon
, “
Benefits of cochlear implantation for patients with single-sided deafness: Data from the House Clinic–University of Southern California–University of California, Los Angeles Clinical Trial
,”
Ear Hear.
40
(
4
),
766
781
(
2019
).
8.
G. M.
Haase
,
K. N.
Prasad
,
W. C.
Cole
,
J. M.
Baggett-Strehlau
, and
S. E.
Wyatt
, “
Antioxidant micronutrient impact on hearing disorders: Concept, rationale, and evidence
,”
Am. J. Otolaryngol.
32
,
55
61
(
2011
).
9.
G. M.
Haase
and
K. N.
Prasad
, “
Oxidative damage and inflammation biomarkers: Strategy in hearing disorders
,”
Otol. Neurotol.
37
,
e303
e308
(
2016
).
10.
R. C.
Bilger
, “
Psychoacoustic evaluation of present prostheses
,”
Arch Otorhinolaryngol.
86
,
92
104
(
1977
).
11.
A.
Mudry
and
M.
Mills
, “
The early history of the cochlear implant: A retrospective
,”
JAMA Otolaryngol. Head Neck Surg.
139
(
5
),
446
453
(
2013
).
12.
A.
Parkinson
,
J.
Varcarolis
,
S.
Staller
,
P.
Arndt
,
A.
Cosgrave
, and
K.
Ebinger
, “
The Nucleus 24 contour cochlear implant system: Adult clinical trial results
,”
Ear Hear.
23
,
41S
49S
(
2002
).
13.
C. G.
Le Prell
,
C. C.
Brewer
, and
K. C. M.
Campbell
, “
The audiogram: Detection of pure-tone stimuli in ototoxicity monitoring and assessments of investigational medicines for the inner ear
,”
J. Acoust. Soc. Am.
152
(
1
),
470
490
(
2022
).
15.
S.
Staller
,
A.
Parkinson
,
J.
Barcarole
, and
P.
Arndt
, “
Pediatric outcomes with the Nucleus 24 contour: North American Clinical Trial
,”
Ann. Otol. Rhinol. Laryngol.
111
,
56
61
(
2002
).
16.
The ASHA Leader Live, June/July (
2020
).
17.
S. C. L.
Kuo
and
W. P. R.
Gibson
, “
The role of the promontory stimulation test in cochlear implantation
,”
Cochlear Implants Int.
3
(
1
),
19
28
(
2002
).
18.
J.
Shallop
,
P. L.
Arndt
, and
P.
Turnacliff
, “
Expanded indications for cochlear implantation: Perceptual results in seven adults with residual hearing
,”
JSLPA
16
(
2
),
141
148
(
1992
).
19.
M.
Armstrong
and
P.
Pegg
, “
Speech perception in noise with implant and hearing aid
,”
Am. J. Otol.
18
,
S140
S141
(
1997
).
20.
C.
Dunn
,
R.
Tyler
, and
S.
Witt
, “
Benefit of wearing a hearing aid on the unimplanted ear in adult users of a cochlear implant
,”
J. Speech. Lang. Hear. Res.
48
(
3
),
668
680
(
2005
).
21.
J.
Kronenberg
,
L.
Maguro
,
R.
Taitelbuam-Sead
, and
M.
Hildesheimer
, “
Bilateral cochlear implantation
,”
Harefuah
149
(
6
),
362
364
(
2010
).
22.
T. Y.
Ching
,
E.
van Wanrooy
, and
H.
Dillon
, “
Binaural-bimodal fitting or bilateral implantation for managing severe-to-profound deafness: A review
,”
Trends Amplif.
11
(
3
),
161
192
(
2007
).
23.
T. M.
Grieco-Calub
and
R. Y.
Litovsky
, “
Spatial acuity in 2- to 3-year old children with normal acoustic hearing, unilateral cochlear implants, and bilateral cochlear implants
,”
Ear Hear.
33
(
5
),
561
572
(
2012
).
24.
K.
Brown
and
C.
Buchman
, “
Benefits of bilateral cochlear implantation: A review
,”
Curr. Opin. Otolaryngol. Head Neck Surg.
15
(
5
),
315
318
(
2007
).
25.
T.
Balkany
,
A.
Hodges
,
F.
Telischi
,
R.
Hoffman
,
J.
Madell
,
S.
Parisier
,
B.
Gantz
,
R.
Tyler
,
R.
Peters
, and
R.
Litovsky
, “
William House Cochlear Implant Study Group: Position statement on bilateral cochlear implantation
,”
Otol. Neurotol.
29
,
107
108
(
2008
).
26.
L.
Dye
,
W. F.
House
, and
C.
O'Connor
, “
Measurable residual hearing following cochlear implantation
,” in
Annual Meeting of the American Academy of Otolaryngology–Head Neck Surgery
(
1987
).
27.
S.
Nguyen
,
F.
Cloutier
,
D.
Philippon
,
M.
Cote
,
R.
Bussieres
, and
D.
Backous
, “
Outcomes review of modern hearing preservation technique in cochlear implant
,”
Auris Nasus Larynx
43
(
5
),
485
488
(
2016
).
28.
J. T.
Roland
,
B.
Gantz
,
S.
Waltzman
, and
A.
Parkinson
, “
United States Multicenter Clinical Trial of the cochlear nucleus hybrid implant system
,”
Laryngoscope
126
(
1
),
175
181
(
2016
).
29.
M. F.
Dorman
and
R. H.
Gifford
, “
Combining acoustic and electric stimulation in the service of speech recognition
,”
Int. J. Audiol.
49
(
12
),
912
919
(
2010
).
30.
R. H.
Gifford
,
M. F.
Dorman
,
H.
Skarzynski
,
A.
Lorens
,
M.
Polak
,
C. L.
Driscoll
,
P.
Roland
, and
C. A.
Buchman
, “
Cochlear implantation with hearing preservation yields significant benefit for speech recognition in complex listening environments
,”
Ear Hear.
34
(
4
),
413
425
(
2013
).
31.
E. L.
von Wallenberg
and
R. D.
Battmer
, “
Comparative speech recognition results in eight subjects using two different coding strategies with the Nucleus 22 channel cochlear implant
,”
Br. J. Audiol.
25
(
6
),
371
380
(
1991
).
32.
G.
Clark
, “
The multiple-channel cochlear implant: The interface between sound and the central nervous system for hearing, speech and language in deaf people—A personal perspective
,”
Philos. Trans. R. Soc. B
361
(
1469
),
791
810
(
2006
).
33.
P.
Seligman
and
H.
McDermott
, “
Architecture of the Spectra 22 Speech Processor
,”
Ann. Otol. Rhinol. Laryngol.
166
,
139
141
(
1995
).
34.
C. T. M.
Choi
and
L.
Yi-Hsuan
, “
A review of stimulating strategies for cochlear implants
,” Cochlear Implant Research Updates 978-953-51-0582-4 (
2012
).
35.
F. G.
Zeng
, “
Trends in cochlear implants
,”
Trends Amplif.
8
(
1
),
1
34
(
2004
).
36.
T.
Balkany
,
A.
Hodges
,
C.
Menapace
,
L.
Hazard
,
C.
Driscoll
,
B.
Gantz
,
D.
Kelsall
,
W.
Luxford
,
S.
McMenomy
,
J. G.
Neely
,
B.
Peters
,
H.
Pillsbury
,
J.
Roberson
,
D.
Schramm
,
S.
Telian
,
S.
Waltzman
,
B.
Westerberg
, and
S.
Payne
, “
Nucleus Freedom North American Clinical Trial
,”
Otolaryngol. Head Neck Surg.
136
(
5
),
757
762
(
2007
).
37.
D. B.
Koch
,
M.
Downing
,
M. J.
Osberger
, and
L.
Litvak
, “
Using current steering to increase spectral resolution in CII and HiRes 90K users
,”
Ear Hear.
28
(
2
),
38S
41S
(
2007
).
38.
D. B.
Koch
,
M. J.
Osberger
,
P.
Segel
, and
D. K.
Kessler
, “
HiResolution and conventional sound processing in the HiResolution Bionic Ear: Using appropriate outcomes measure to assess speech recognition ability
,”
Audiol. Neurotol.
9
,
214
223
(
2004
).
39.
C.
Dunn
,
S. E.
Miller
,
E. C.
Schafer
,
C.
Silva
,
R. H.
Gifford
, and
J. J.
Grisel
, “
Benefits of a hearing registry: Cochlear implant candidacy in quiet versus noise in 1,611 patients
,”
Am. J. Audiol.
29
(
4
),
851
861
(
2020
).
40.
C. L.
Runge
,
K.
Henion
,
S.
Tarima
,
A.
Beiter
, and
T.
Zwolan
, “
Clinical outcomes of the Cochlear Nucleus 5 cochlear implant system and Smart Sound 2 signal processing
,”
J. Am. Acad. Audiol.
27
,
425
440
(
2016
).
41.
P.
Van de Heyning
,
K.
Vermeire
,
M.
Diebl
,
P.
Nopp
,
I.
Anderson
, and
D.
De Ridder
, “
Incapacitating unilateral tinnitus in single-sided deafness treated by cochlear implantation
,”
Ann. Otol. Rhinol. Laryngol.
117
,
645
652
(
2008
).
42.
K.
Smeds
,
F.
Wolters
, and
M.
Rung
, “
Estimation of signal-to-noise ratios in realistic sound scenarios
,”
J. Am. Acad. Audiol.
26
(
2
),
183
196
(
2015
).
43.
Z. S.
Nasreddine
,
N. A.
Phillips
,
V.
Bedirian
,
S.
Charbonneau
,
V.
Whitehead
,
I.
Collin
,
J. L.
Cummings
, and
H.
Chertkow
, “
The Montreal Cognitive Assessment, MoCA: A brief screening tool for mild cognitive impairment
,”
J. Am. Geriatr. Soc.
53
(
4
),
695
699
(
2005
).
44.
V. Y.
Lin
,
J.
Chung
,
B. L.
Callahan
,
L.
Smith
,
N.
Gritters
,
J. M.
Chen
,
S. E.
Black
, and
M.
Masellis
, “
Development of cognitive screening test for the severely hearing impaired: Hearing-impaired MoCA
,”
Laryngoscope
127
(
1
),
S4
S11
(
2017
).
45.
A.
Biever
,
C.
Amurao
, and
M.
Mears
, “
Considerations for a revised adult cochlear implant evaluation protocol
,”
Otol. Neurotol.
42
,
159
164
(
2021
).
46.
E.
Lupo
,
A.
Biever
, and
D. C.
Kelsall
, “
Comprehensive hearing aid assessment in adults with bilateral severe-profound sensorineural hearing loss who present for cochlear implant evaluation
,”
Am. J. Otololaryngol.
41
,
102300
(
2020
).
47.
T. R.
McRackan
,
B. N.
Hand
,
C. A.
Velozo
, and
J. R.
Dubno
, and
Cochlear Implant Quality of Life Consortium
,
Validity and reliability of the Cochlear Implant Quality of LIFE (CIQOL)-35 Profile and CIQOL-10 Global instruments in comparison to legacy instruments
,”
Ear Hear.
42
(
4
),
896
908
(
2021
).
48.
D.
Fabry
,
J. B.
Firszt
,
R. H.
Gifford
,
L. K.
Holden
, and
D. B.
Koch
, “
Evaluating speech perception benefit in adult cochlear implant recipients
,”
Audio Today
21
,
36
43
(
2009
).
49.
R. H.
Gifford
,
J. K.
Shallop
, and
A.
Peterson
, “
Speech recognition materials and ceiling effects: Considerations for cochlear implant programs
,”
Audiol. Neurotol.
13
,
193
205
(
2008
).
50.
A. J.
Spahr
,
M. F.
Dorman
,
L. M.
Litvak
,
S.
Van Wie
,
R. H.
Gifford
,
P. C.
Loizou
,
L. M.
Loiselle
,
T.
Oakes
, and
S.
Cook
, “
Development and validation of the AzBio sentence lists
,”
Ear Hear.
33
,
112
117
(
2012
).
51.
R.
Gifford
and
M.
Dorman
, “
Bimodal hearing or bilateral cochlear implants: Ask the patient
,”
Ear Hear.
40
(
3
),
501
516
(
2019
).
52.
K.
Uhler
,
A.
Warner-Czyz
, and
R.
Gifford
, and
Working Group
, “
Pediatric Minimum Speech Test Battery
,”
J. Am. Acad. Audiol.
28
(
3
),
232
247
(
2017
).
53.
C.
Buchman
,
R.
Gifford
,
D.
Haynes
,
T.
Lenarz
,
G.
O'Donoghue
,
O.
Adunka
,
A.
Biever
,
R. J.
Briggs
,
M. L.
Carlson
,
P.
Dai
,
C. L.
Driscoll
,
H. W.
Francis
,
B. J.
Gantz
,
R. K.
Gurgel
,
M. R.
Hansen
,
M.
Holcomb
,
E.
Karltorp
,
M.
Kirtane
,
J.
Larky
,
E. A. M.
Mylanus
,
J. T.
Roland
, Jr.
,
S. R.
Saeed
,
H.
Skarzynski
,
P. H.
Skarzynski
,
M.
Syms
,
H.
Teagle
,
P. H.
Van de Heyning
,
C.
Vincent
,
H.
Wu
,
T.
Yamasoba
, and
T.
Zwolan
, “
Unilateral cochlear implants for severe, profound, or moderate sloping to profound sensorineural hearing loss. A systematic review and consensus statements
,”
JAMA Otolaryngol. Head Neck Surg.
146
(
10
),
942
953
(
2020
).