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Raman G, Lee J, Chung Met al., authors; Sen S, editor. Effectiveness of Cochlear Implants in Adults with Sensorineural Hearing Loss [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2011 Jun 17.
This publication is provided for historical reference only and the information may be out of date.
Effectiveness of Cochlear Implants in Adults with Sensorineural Hearing Loss [Internet].
Show detailsOur search of the FDA Web site found three cochlear implant devices currently approved for use in the U.S. We searched for articles on cochlear implants in adults published between January 2004 and February 2011 in the MEDLINE®, Scopus (which includes articles indexed in Embase since 1997) and Cochrane Central databases and found 56 out of 1,908 articles that met our inclusion criteria (Appendix C). Detailed descriptions of individual studies are provided in summary tables available in Appendix D.
Key Question 1
What current cochlear implantation devices are approved by the FDA for individuals ≥ 18 years of age? What are the indications for their use?
In the 1970s, the FDA recommended implantation for adults only with profound hearing loss4, and in 1985 approved the use of multi-channel cochlear implant devices for adults aged 18 and older, postlinguistically deaf with bilateral profound sensorineural hearing loss, and an aided speech recognition score of 0 percent, indicating little or no open-set sentence discrimination. Our search of the FDA Web site found three cochlear implant systems (comprised of the implant itself along with the external microphone, sound processor, and transmitter system) that currently have market approval. These three devices are respectively produced by three manufacturers: Cochlear™ Americas (Australia; Centennial, CO, USA), Advanced Bionics® (Valencia, CA, USA), and MED-EL (Austria; Durham, NC, USA). Their indications and contraindications for adult use are described by the FDA, or when not available, directly by the manufacturer; these are summarized in Table 1. A fourth company—Racer Technology PTE LTD (Singapore)—was also listed as a currently registered manufacturer, but with no further details. The search in ClinicalTrials.gov revealed no new or emerging devices or manufacturers.
Table 1
Cochlear Implantation devices currently approved by the FDA.
Candidates for Cochlear Implants
Initial use of cochlear implants was restricted to adults who were postlinguistically deaf with profound hearing loss. Over the past few decades these criteria have been gradually expanded to include adults with residual hearing who are either prelinguistically or postlinguistically deaf with moderate-to-profound loss in the low frequencies or profound loss in the mid-to-high frequencies of sound. Candidates for cochlear implants include adult subjects with severe-to-profound, pre or postlinguistic (sensorineural) hearing loss defined as a hearing threshold of pure-tone average of 70 dB (decibels) hearing loss or greater at 500 hertz (Hz), 100 Hz, and 2000 Hz, and have shown limited or no benefit from hearing aids. Criteria for cochlear implant candidacy are variable across devices and individual to each. Based on the safety and efficacy information provided to the FDA by each device manufacturer, likely candidates could have percent correct scores on the Hearing in Noise Test (HINT) or open–set sentence recognition tests ranging from ≤ 40 to ≤ 60 percent (depending on the device as described in Table 1). There is no upper age limit for candidacy.5
Recalls
A grey literature search identified three recalls of cochlear implants; each recall was that of an Advanced Bionics device. It should be noted here, however, that data regarding any import bans of devices manufactured outside of the U.S. due to malfunction or potential malfunction—which are in essence equivalent to recalls—were not found in our search and might not be readily available in a grey literature search; therefore, recall results summarized here could be biased. The first was a voluntary recall in 2004 of unimplanted Clarion and HiResolution cochlear implants because of a potential for malfunction due to moisture within the receiver-stimulator. In 2006, a similar recall was undertaken for unimplanted HiRes 90K® devices that were manufactured by a particular supplier to Advanced Bionics, again because of a potential for device failure due to elevated moisture levels. In both recalls, patients and practitioners were advised to monitor already-implanted patients for intermittent function, complete loss of sound, sudden discomfort, pain, noise, or popping; explantation was not recommended for non-failed devices.
In November 2010, Advanced Bionics issued a voluntary recall of implanted HiRes 90K® devices (though the device maker noted that the risk of significant adverse events is currently remote) and is retrieving all unimplanted devices in response to two instances out of 28,000 devices where the product experienced a malfunction requiring explantation within 8-10 days of device activation.
Key Question 2
What are the communication-related health outcomes as well as the quality-of-life outcomes that are achieved in the population of adults (≥ 18 years old) who undergo unilateral cochlear implantation? How is a “successful” implantation defined?
Study Characteristics
A total of 22 studies each with ≥ 30 subjects with unilateral cochlear implants met our inclusion criteria and addressed the effectiveness of unilateral cochlear implantation. Of these, six were prospective studies, 10 retrospective studies, and five cross-sectional studies. The baseline characteristics of these studies are presented in Table 2. Among the studies, the number of subjects varied from 30 to 864, and the mean baseline age ranged from 37 to 74 years. The studies were mainly conducted in the U.S. (six studies), followed by the Netherlands and UK (three studies in each country). The quality of the studies was graded fair (nine quality-B studies) to poor (13 quality-C studies), due to limitations in study design and reporting of baseline characteristics.
Table 2
Summary of baseline characteristics of the included studies for KQ2.
Study Results
Speech perception measures
Open-set sentences tests
The overall evidence for the effectiveness of unilateral cochlear implants on speech perception using open-set sentences tests was rated moderate because the results were consistent across the five quality-B studies. Twelve studies assessed speech perception employing six open-set sentences tests (Table 3): AzBio sentences in one study;11 Bamford Kowal Bench (BKB) sentences in three studies;8, 17, 24 Central Institute for the Deaf (CID) sentences in one study;21 City University of New York (CUNY) test in four studies;9, 18, 20, 24 Hearing in Noise Test (HINT) in seven studies;9, 11, 12, 18, 22, 23, 28 and Hochmair-Schultz-Moser (HSM) test in one study.15 One study did not specify the “open-set sentences” test used to measure speech perception.29
Table 3
Summary results of speech perception measures in unilateral cochlear implants.
Pre versus postunilateral cochlear implants
Thirteen studies (14 publications) used participants as their own control to compare post with preimplantation speech perception.8, 9, 11, 12, 15, 17, 18, 20-24, 28, 29 All or most of the quality-B studies that compared unilateral cochlear implantation with preimplantation showed a significant clinical benefit and most of the quality-C studies showed a statistically non-significant but clinical benefit after unilateral cochlear implantation.
The UK Cochlear Implant Study Group [UKCISG] (n=316) study, rated quality-B, evaluated the effectiveness of unilateral cochlear implants on speech perception.24 They used two open-set sentences tests (i.e., the BKB sentence test and the audiovisual gain for CUNY sentence test) and calculated the standardized response mean difference between pre and postimplantation at 9 months. Both speech perception measures showed large effects at post compared with precochlear implantation: effect size (ES) = 1.50 for BKB, and ES = 1.78 for CUNY.
One quality-B study found that postimplantation percent scores of two syllable tests were significantly increased to 52 percent, 62 percent, and 54 percent at 1, 2, and 3 years of followup, respectively, compared with preimplantation scores of 20 percent.21
Unilateral cochlear implants versus hearing aids
There was only one cross-sectional study of quality-C (that met the inclusion criteria) that compared unilateral cochlear implant users with hearing aid users.11 Gifford 2008 conducted cross-sectional analysis of retrospectively collected data. The study included 143 unilateral implants, 13 bilateral implants, as well as 50 hearing aid users; results of bilateral implants from this study are discussed under Key Question 3. All speech perception tests were presented at the 60 dB SPL. The group means for HINT sentences in quiet were significantly higher in unilateral implants (84.8 percent) and bimodals (94.1 percent) versus hearing aid users (73.1 percent). Similarly for the AzBio sentence recognition, the performance was significantly higher in unilateral implants (72.1 percent) and bimodals (83.5 percent) versus hearing aid users (47.3 percent). The scores among hearing aid users (15.2 dB) were poorer in BKB-SIN test compared with unilateral implants (11.4 dB) and bimodals (8.7 dB).
Generic quality-of-life measures
The overall evidence for the effectiveness of unilateral cochlear implants on quality-of-life using generic measures was rated moderate because the results were consistent across the six quality-B studies. In general, there were significant effects from the use of unilateral cochlear implants on overall health-related quality-of-life and social domains in quality-B studies; the one quality-B study and most of the quality-C studies did not show significant effect on physical, cognitive, and emotional domains (Table 4).
Table 4
Summary results of health-related quality-of-life (generic) in unilateral cochlear implants.
Pre versus postunilateral cochlear implants
Ten studies evaluated health-related quality-of-life using generic measures, mainly the Glasgow Benefit Inventory (GBI), Glasgow Health Status Inventory (GHSI), Health Utilities Index (HUI), and Short-Form (SF)-36 (Table 4).8, 10, 13, 14, 16, 19, 20, 24, 25, 27
Damen 2007 conducted a long-term (up to 6 years) followup study to examine health-related quality-of-life by comparing pre and postimplantation using the two generic health-related quality-of-life instruments (i.e., SF-36 and HUI-3).10 A group of 22 shorter term cochlear implant users (< 6 years) showed significant benefits on hearing, emotion, and HUI-3 utility for HUI-3 results; and mental health and mental summary score for Short Form (36) Health Survey (SF-36) results. The other group of 37 longer term cochlear implant users (≥ 6 years) showed a slight decrease in HUI and SF-36 over time.
The UKCISG examined the effectiveness of unilateral cochlear implants for generic health-related quality-of-life. Nine-month postimplantation showed large benefits on GHSI (ES=1.22) and HUI3 (ES=1.05) as compared with preimplantation.24
In one cross-sectional study, postimplantation also showed significant benefits on all SF-36 subdomains (i.e., energy, social function, psychological well-being) compared with preimplantation.27
Disease specific quality-of-life measures
The overall evidence for the effectiveness of unilateral cochlear implants on health-related quality-of-life using disease-specific measures was rated moderate because the results were consistent across the four quality-B studies.
Six studies assessed quality-of-life employing the following disease-specific assessments (Table 5): Adapted Deaf Identity Developmental Scale for one study;19 Hearing Handicap Inventory for Adults (HHIA) for two studies;25, 26 Hearing Participation Scale (HPS) for one study;13 and Nijmegen Cochlear Implant Questionnaire (NCIQ) for two studies.10, 14
Table 5
Summary results of health-related quality-of-life (disease-specific) in unilateral cochlear implants.
Pre versus postunilateral cochlear implants
Five studies with disease specific measures (HHIA, HPS, and NCIQ) showed significant benefits on health-related quality-of-life from unilateral cochlear implants compared with preimplantation measures.10, 13, 14, 19, 25, 26 However, one study that used the Adapted Deaf Identity Developmental Scale found no statistical difference in family relations between post and preimplantation. This study did show significant effects on communication, social skills, academic and work performance, and general satisfaction with unilateral cochlear implants.19
Key Question 2a
For adult individuals (≥ 18 years of age) with sensorineural hearing loss, what are the preoperative patient characteristics associated with the successful attainment of the above improved communication-related health outcomes as well as quality-of-life outcomes in those who undergo unilateral cochlear implantation?
The overall evidence for the duration of impaired hearing, age at implantation, and type of implanted devices as preoperative predictors of postoperative speech outcomes after unilateral cochlear implants was rated moderate, low, and low, respectively, based on consistent results among quality-B studies. The overall evidence for other preoperative predictors, including older age (≥65 years old), preoperative speech perception scores was rated insufficient.
Study Characteristics
Twenty one studies analyzed preoperative patient characteristics as potential modifying factors of postoperative speech perception outcomes (open-set sentences, two syllable words) and/or health-related quality-of-life outcomes.9, 12-14, 18, 20, 24, 25, 28-40 Of these, 4 were prospective cohort studies;13, 14, 24, 38 13 were retrospective cohort studies (in 14 publications);9, 12, 18, 20, 28-30, 32-35, 37, 39, 40 one was a case-control study;30 and 3 were cross-sectional studies.25, 31, 36 Followup durations ranged from 6 months to 1 year for prospective studies, and 1 to 12 years for retrospective studies. All four prospective studies were of quality-B; four retrospective studies were of quality-B, and the remaining 10 were quality-C; all cross-sectional studies were of quality-C. None of the C-quality studies (neither retrospective nor cross sectional) accounted for potential confounding factors in their analyses. Other common methodological deficiencies included missing data and poor reporting of patient characteristics.
The studies were generally small in sample size, ranging from 22 to 316 patients with cochlear implants. Mean age of patients ranged from 37 to 74 years. Of the 21 studies, eight reported the baseline severity of deafness of enrolled patients, ranging from severe-to-profound hearing loss. Average duration of deafness ranged from 13 to 16 years among patients in the prospective cohort studies (reported in 3 studies), from 8 to 32 years among patients in the retrospective studies (reported in 7 studies), and from 6 to 13 years among patients in the cross-sectional studies (reported in 2 studies). Time between onset of deafness and cochlear implantation or indication for cochlear implant were poorly reported (i.e., only 5 studies reported relevant information). Table 6 summarizes the baseline characteristics of the 21 studies.
Table 6
Summary of baseline characteristics of the included studies for KQ 2a.
Potential preoperative patient characteristics that were examined in the 21 studies included: duration of impaired hearing (7 studies), age of implantation (7 studies), older [≥ 65 years old] versus younger age [< 65 years old] (7 studies), type of implanted device (7 studies), preoperative speech recognition or word understanding (5 studies), degree of preimplant residual hearing (4 studies), associated ear or bone diseases (2 studies), pre versus postlinguistic deafness (2 studies), age at onset of hearing loss (2 studies), and choice of implanted ear (1 study). We found no studies that examined implant center/expertise of cochlear implant teams or other patient-related disabilities as potential modifying factors of speech and/or health-related quality-of-life outcomes. Table 7 shows summary findings tabulated by potential preoperative modifying factors and postoperative outcomes.
Table 7
Results from studies evaluating the association between preoperative characteristics and outcomes.
Study Results
Duration of impaired hearing
Seven studies (5 quality-B,13, 14, 24, 35, 39 2 quality-C12, 37) with a total of 627 patients with a cochlear implant examined the duration of preoperative impaired hearing as a potential modifying factor of postoperative speech perception or health-related quality-of-life outcomes.
Five studies (3 quality-B, 2 quality-C) reported speech outcomes. Of these, three quality-B studies found that longer duration of preoperative impaired hearing was significantly correlated with poorer speech outcomes as measured by CUNY and/or BKB scores.24, 35, 39 Another study (quality-C) reported that, among the younger adults (< 65 years old), longer duration of hearing loss before cochlear implantation was associated with better speech reading skill as measured by HINT (r= 0.86; P= 0.003), but this association was not significant among older adults (≥ 65 years old).13 The last study (quality-C) found no significant differences in the duration of impaired hearing between patients who had high postoperative speech performance (BKB score > 47 percent) and those who had low postoperative speech performance (BKB score ≤ 47 percent).37 This definition of high speech performance, a BKB score > 47 percent was based on the 25th percentile of the BKB data among study participants whose score was 47 or more percent correct.
Two studies (both quality-B) reported health-related quality-of-life outcomes. In one study, longer duration of preoperative impaired hearing was significantly correlated with better postoperative (general and hearing-specific) quality-of-life after controlling for other potential confounders.14 However, another study found that duration of preoperative impaired hearing was not significantly associated with postoperative (general and hearing-specific) quality-of-life.13
Age at implantation
Seven studies (3 quality-B,14, 35, 39 4 quality-C12, 28, 30, 32) with a total of 593 patients with a cochlear implant examined age at implantation as a potential modifying factor of postoperative speech perception or health-related quality-of-life outcomes.
Six studies (2 quality-B, 4 quality-C) reported speech outcomes. Overall, in none of the studies was there a significant correlation between age at implantation and postoperative speech outcomes as measured by HINT, CUNY, or BKB. One quality-C study of only older adults (≥ 65 years old) reported that although the age at implantation was not associated with postoperative HINT scores in a quiet environment, older age at implantation was marginally correlated with better HINT scores under noise conditions (r=0.40; P=0.05).30
One quality-B study reported health-related quality-of-life outcomes. This study showed that younger age at implantation was associated with better hearing-specific quality-of-life outcomes.14
Older age (≥ 65 years old)
Seven quality-C studies12, 20, 25, 30, 31, 33, 40 with a total of 807 patients with a cochlear implant examined whether older age (≥ 65 years) versus younger age (< 65 years) is a potential modifying factor of postoperative speech perception or health-related quality-of-life outcomes.
Six quality-C studies reported speech outcomes. Overall, most of the studies found significant differences in postoperative speech perception outcomes as measured by HINT, CUNY, BKB and/or speech perception between older (≥ 65 years old) and younger (< 65 years old) patients. One study found that older patients had a significantly lower postoperative HINT score in quiet conditions than younger patients (70 percent vs. 83 percent, respectively; P=0.02).30 However there was no significant difference in HINT score in noise conditions between the two groups. Another study showed that older (≥ 80 years old) patients had a significantly higher postoperative AzBio sentence recognition score than younger (< 80 years old) patients.40 However, there was no significant difference in BKB scores in noise conditions between the two groups.
One quality-C study reported health-related quality-of-life outcomes. This study found no significant differences in general or hearing-specific quality-of-life outcomes between young (≤ 55 years old), middle (56 to 69 years olds), and geriatric (≥ 70 years old) patients.25
Implanted device
Seven studies (2 quality-B,35, 38 5 quality-C28, 29, 32, 36, 37) with a total of 625 patients with a cochlear implant examined type of implant device as a potential modifying factor of postoperative speech perception outcomes. Five of the seven studies did not find significant differences in postoperative speech perception outcomes as measured by HINT, CUNY, BKB and/or CPA recognition tests (Centro de Pesquisas Audiológicas recognition test at different noise ratios) among patients who received different cochlear implant devices. One quality-B study showed that, although there was no significant differences in CUNY and BKB scores, patients who received an Advance Bionics CII implant had significantly higher AzBio sentence scores than patients who received a Nucleus 3G implant (75 vs. 61%, P=0.01).38 One quality-C study found that patients with a new model of cochlear implant (Nucleus® Freedom™) had higher HINT auditory scores in noisy conditions than patients with older models (Nucleus® 22 or 24) (89 vs. 73%, P=0.01).28 Another quality-C study showed similar findings comparing another new model of cochlear implant (Digisonic® SP) with its older model (Digisonic® Convex), but did not report what “open set sentences” test was used to measure the speech perception outcomes.29 Neither of these two models (Digisonic® SP or Digisonic® Convex) have been approved by the FDA and thus are not available in the United States.
Preoperative speech perception scores
Five studies (2 quality-B,14, 30 3 quality-C28, 30, 40) with a total of 468 patients with a cochlear implant examined preoperative speech perception as a potential modifying factor of postoperative speech perception or health-related quality-of-life outcomes.
Four studies (1 quality-B, 3 quality-C published in three publications) reported speech perception outcomes. Results were mixed. Two studies (1 quality-B; 1 quality-C) found that a better preoperative HINT score was significantly associated with a better postoperative HINT score (cohort study: r= 0.44; P=0.02; case-control study: r=0.31; P=0.02).30 The other two quality-C studies did not find significant relationships between preoperative and postoperative speech recognition scores as measured by HINT auditory and audiovisual or AzBio sentences tests.28, 40
One quality-B study reported health-related quality-of-life outcomes. This study showed that better preoperative CVC (consonant-voice-consonant word list) score was significantly associated with better postoperative general quality-of-life score (multivariate regression beta coefficient= 0.0003; P=0.02).14
Degree of preimplant residual hearing as defined by pure tone thresholds
Four studies (2 quality-B,13, 35 2 quality-C34, 40) with a total of 423 patients with a cochlear implant examined degree of preimplant residual hearing as a potential modifying factor of postoperative speech perception or health-related quality-of-life outcomes.
Three studies (1 quality-B, 2 quality-C) reported speech outcomes. None found a significant association between degree of preimplant residual hearing and postoperative speech perception outcomes as measured by HINT, BKB, or AzBio sentences.34, 35, 40
One quality-B study reported health-related quality-of-life outcomes. This study found that postoperative general quality-of-life improved more among patients who had “profound deafness” than those who had “severe-moderate deafness” [Note: severity of deafness was not defined in the original article] (P=0.08).13 However, there were no significant differences in hearing-specific quality-of-life outcomes between the two groups of patients.
Associated ear or bone diseases
Two quality-C studies32, 37 with a total of 62 patients with a cochlear implant examined associated ear or bone disease as a potential predictor of postoperative speech perception outcomes. One study found no significant difference in the proportion of patients with varying clinical types of otosclerosis (types 1 to 3) when comparing patients with high postoperative speech performance (BKB score > 47 percent) and those with low postoperative speech performance (BKB score ≤ 47 percent).37 This definition of high speech performance, a BKB score > 47 percent was based on the 25th percentile of the BKB data among study participants whose score was 47 percent correct. Another study also found no difference in the percentage of patients with normal temporal bone when comparing patients with excellent or poor postoperative speech performance.32 Poor performers were defined as patients who realized a worsening, no improvement, or an improvement of less than 10 percent in their audiologic scores.
Post versus prelinguistic deafness
Two quality-C studies9, 32 with a total of 339 patients with a cochlear implant examined whether postlinguistic deafness (versus prelinguistic deafness) was a potential modifying factor of postoperative speech perception outcomes. Both studies found that postlinguistic deafness was significantly associated with better postoperative speech outcomes as measured by HINT, CUNY, or BKB, when compared with prelinguistic deafness.
Age at onset of hearing loss
Two quality-C studies12, 37 with a total of 62 patients with a cochlear implant examined the age at onset of hearing loss as a potential modifying factor of postoperative speech perception outcomes. One study found no significant relationship between age of hearing loss onset and postoperative BKB score.37 The other study found that, among the younger adults (< 65 years old), earlier age of hearing loss onset was significantly associated with poorer speech reading skill as measured by HINT, but this association was not significant among older adults (≥ 65 years old).13
Choice of implanted ear
One quality-B study18 with 101 patients with a cochlear implant examined the choice of implanted ear as a potential modifying factor of postoperative speech outcomes. This study did not find significant association between right- and left-ear implant and postoperative speech outcomes as measured by HINT and CUNY.
Key Question 2b
Of studies included for Key Question 2 and Key Question 2a, are there data available separately for those individuals with sensorineural hearing loss as demonstrated by test scores of > 40 percent and ≤ 50 percent, as well as those with test scores > 50 percent and ≤ 60 percent (best aided listening on tape or otherwise recorded tests of open-set sentence recognition)?
Of the 22 studies that evaluated key question 2, there were no studies that used the results of open-set sentence tests for cochlear implantation indication.
Of the 21 qualifying studies that evaluated key question 2a, only two (one quality-B; one quality-C) provided relevant data for this question.30, 33 The quality-B study analyzed a retrospective cohort of 78 elderly (≥ 70 years old) patients for the associations between preimplant HINT scores (≤20%, 21-40%, ≥40%), and 1-year postimplant HINT scores. Elderly with preimplantation HINT-Q scores below 20 percent, of 20 through 40 percent, and to 41 percent or greater were analyzed with respect to 1-year postimplant HINT-Q scores. The results indicated that better preimplant HINT-Q scores showed significant association with higher postimplant HINT-Q (r=0.44, P=0.02), and HINT-N (r=0.43, P=0.04) scores regardless of age.
The quality-C study was based on a retrospective chart review. Only adults implanted with either the Clarion device or Nucleus device between 1991 and 2002 were included in the analyses. The criteria for cochlear implantation included severe to profound hearing loss in both ears (mean 70 dB) and a score of less than 50 percent on an open-set sentence test using conventional hearing aid(s). Sixty-five elderly adults (≥ 70 years old) were compared with 101 younger adults (< 70 years old) for speech outcomes. The study found that both elderly and younger adults had significant improvements in HINT and CID scores after implantation. However, there were no significant differences between groups (P=0.07). This analysis was not adjusted for potential confounding factors.
Two studies reported information on the indication of cochlear implantation for study participants, although these studies did not use the term ‘indications’ as specified in the key question. The criteria for cochlear implantation used in these studies include pure-tone threshold > 90 dB hearing loss or phoneme recognition of < 40 percent,14 and monosyllabic word recognition of < 30 percent (open-set; 70 dB).31 For these two studies, Table 7 shows summary findings tabulated by potential preoperative modifying factors and postoperative outcomes. The first study showed that younger age at implantation was associated with better hearing-specific quality-of-life outcomes.14 The second study found significant differences in postoperative speech perception outcomes between older (≥ 65 years old) and younger (< 65 years old) patients.31
Key Question 3
For those individuals ≥ 18 years of age, what are the additional communication-related health outcomes as well as quality-of-life outcomes (as compared to those achieved in Key Question 2) that are gained from the use of bilateral cochlear implants over a unilateral cochlear implant? How is a “successful” bilateral cochlear implant defined?
Evidence was rated moderate to low based on data from nine studies assessing subjects with simultaneous or sequential bilateral cochlear implantation that were graded a methodological quality of B. Overall, 16 studies published since 2004 evaluated subjects with bilateral cochlear implants that met our eligibility criteria. Summary of baseline characteristics is provided in Table 8. Studies evaluating speech perception in noise conditions found significant gains with bilateral simultaneous cochlear implants compared with a unilateral cochlear implant. One cross-sectional study showed no benefit and another study did not evaluate speech outcomes. The results of speech perception in quiet and health-related quality-of-life were mixed across studies. Only three of nine studies assessed health-related quality-of-life in subjects with bilateral implants. While subjects with bilateral cochlear implants showed significant gains in some health-related quality-of-life subscales, others found no difference between the two groups. In a randomized controlled trial evaluating sequential bilateral cochlear implants, the second ear implant resulted in negative or non-significant results for quality-of-life after the first ear implant.
Table 8
Summary of baseline characteristics of the included studies for bilateral simultaneous and sequential cochlear implant.
Simultaneous Bilateral Cochlear Implantation
Evidence was rated moderate to low based on data from seven studies that were graded a methodological quality-B. In total, nine studies assessed subjects with simultaneous bilateral cochlear implantation that were graded a methodological quality of B or C. Of these eight studies evaluating speech perception using open-set sentences or multi-syllable tests found gains with bilateral simultaneous cochlear implants compared with a unilateral cochlear implant or unilateral listening condition. All five studies evaluating sound localization reported significant bilateral benefit over unilateral listening condition. However, only two studies assessed disease specific health-related quality-of-life. While subjects with bilateral cochlear implants showed significant gains in some health-related quality-of-life subscales such as lower social restriction, no difference between the two groups was reported in other subscales.
Study Characteristics
Nine studies of quality-B or -C (a total of 451 subjects) in ten publications compared simultaneous bilateral cochlear implants with unilateral cochlear implantation.41-50 Six were prospective studies with followup durations of 3 months to 1 year,43, 44, 46, 48-50 and the remaining three were cross-sectional design studies.11, 41, 42, 45 All studies were conducted in the U.S. except for one study that was conducted in France.50 The mean or the median age of included subjects at cochlear implantation ranged from 46 to 64 years. The proportion of males included in studies ranged from 31 and 47 percent. Studies recruited subjects with severe to profound hearing loss for a mean duration of 3.5 to 15 years. Only two of the six studies reported that subjects were required to have an open-set sentence score of ≤ 50 percent in the best-aided condition as an indication for cochlear implantation.43, 44 Bilateral simultaneous cochlear implantation was compared with either ear unilaterally within subjects, 41, 43, 44, 46, 48-50 or was compared with different subjects with unilateral cochlear implantation (with or without hearing aid use).42, 45 There could be considerable overlap of subjects in the two studies.41, 45 Seven studies were graded quality-B, (moderate) 42-44, 46, 48-50 and the remaining two studies were graded quality-C (poor).41, 45 In general, the studies lacked reporting of baseline characteristics, and had considerable differences in methodologies including duration of deafness, implanted devices, speech coding strategies, and tests for evaluation (Appendix Table D8 – D9).
Study Results
Speech perception with open-set sentences tests
Seven studies evaluated open-set sentences tests including, BKB-SIN (speech in quiet or in noise), CUNY sentences in noise, and HINT (speech in quiet or in noise).41, 43, 44, 46, 48-50 Of these, three studies examined BKB-SIN test; one study tested in nine test conditions, which included three listening conditions and three noise locations44 or as speech in babble task.48, 49 In Litovsky 2006, a bilateral listening condition was better than either ear unilaterally at 3 and 6 month intervals. In Litovsky 2009, bilateral listening with both ears benefitted most as compared with one ear, when the target and interfering speech-in-babble task was spatially separated and 82 percent of subjects had bilateral benefit for correct hemi field identification. When target speech and babble were collocated at 0° azimuth, 60 percent of subjects benefitted at 3 months and 53 percent at 6 months of postbilateral activation. In Litovsky 2004, bilateral benefit against poorer ear was significant, while bilateral benefit against better ear was minimal. All three studies that tested HINT sentences in quiet,41, 43, 44 reported that bilateral cochlear implants scored statistically significantly better than the unilateral cochlear implants (Table 9). Buss 2009 reported bilateral listening was significantly better than unilateral listening during 1 year followup. While SNR values decreased between an interval of 3 months to 6 months, this did not reach statistical significance; of note, SNR values decreased significantly during an interval of followup between 6 months and 1 year.
Table 9
Open-set sentences and multi-syllable tests in subjects with bilateral simultaneous cochlear implant.
Speech perception with multi-syllable tests
Two studies evaluated speech perception using a multiple-jammers test or disyllabic words.42, 50 One study (60 subjects) conducted a multiple-jammers test using the target spondee words and sentences as combinations of randomly selected male and female sentences (jammers) that were presented simultaneously from one of the two speakers placed at ±8° from 0° azimuth. On the multiple-jammers tests, the bilateral cochlear implant group performed statistically significantly better than the unilateral cochlear implant group (Table 9).42 The bilateral cochlear implant group listened better against significantly higher noise levels (9 dB more) to identify words 50 percent of the time compared with the unilateral cochlear implant group. This study also showed that the bilateral cochlear implant group scored significantly better at processing speech by 11 dB SNR while attending to other simultaneous activities as identified by their scores in the Cognitive load test. The second study (Mosnier 2009) evaluated 27 subjects for speech performance using disyllabic words in both quiet and noise conditions.50 Bilateral listening versus the better ear (unilateral condition) was better in both quiet and noise conditions at 12 months postactivation, while magnitude of improvement was higher when tested in quiet and was slightly lower when tested in noise. This study reported that at 6 months, subjects were able to identify words at low SNR of +5dB in bilateral listening condition, and had benefit over unilateral condition. However, the bilateral benefit at 12 months was largely similar at +5 dB and at +15 dB.
Additional outcomes of binaural processing
Litovsky 2006 reported that between 3 and 6 months, an overall improvement in BKB-SIN test performance occurred under most of the listening conditions as well as most of the noise locations, suggesting that bilateral implantation aided participants to overcome the “head shadow effect” when in noise. The “head shadow effect” refers to the “shadow” or partial blockage of sound created when the head and shoulders are interposed between a sound source and the opposite sided implant (or hearing ear). The reduction of speech perception by the “head shadow effect” is amplified in the presence of background noise. However, noise from the frontal location (0° azimuth) resulted in a significantly poorer performance than when the noise was from either side of the head. For the noise from the front, there was no difference between the right and left ear. Buss 2009 reported binaural benefits in derived measures of head shadow effect, squelch, and summation during 1 year followup.
Sound Localization
All studies tested sound localization in quiet and one study in noise with the use of speakers in varying numbers located in a frontal plane, as well as different types of sound stimuli. Although there was an overall improvement in sound localization ability in bilateral listening compared with unilateral listening conditions, there was considerable inter-subject variability in at least three studies. Grantham 2007 reported that subjects with both ear implants localized speech signal better than noise signal.47 Mosnier 2009 additionally tested speech localization in the presence of five noise sources that was similar to a cocktail party setting and reported large individual differences among 44 percent of a total of 27 subjects.50 While 82 percent of a total of 17 subjects demonstrated bilateral benefit when right or left discrimination was evaluated at 3 months of postactivation in Litovsky 2009, only 47 percent subjects had bilateral benefit when sound localization was tested.49
Health-related quality-of-life
Two studies evaluated three different disease-specific instruments.44, 45 One study used four subscales of the Abbreviated Profile of Hearing Aid Benefit (APHAB) to assess the perceived performance of each subject’s real world listening experiences.44 Compared with the best unilateral implant, the quality-of-life with bilateral cochlear implants was significantly better (P<0.0001) in three of four subscales including the ease of communication, listening in reverberant conditions, and background noise (Table 10). No significant difference between the two groups was reported for the subscale of aversiveness to sound. The second study examined two different disease-specific quality-of-life measures using the Hearing Handicap Inventory for the Elderly (HHIE) and the Hearing Handicap Questionnaire (HHQ).45 For both HHIE and HHQ measures, subjects with bilateral cochlear implants had significantly lower social restriction scores compared with those with unilateral cochlear implant (Table 10). However, for the scores of emotional distress, there was no difference between the two groups. None of the studies reported any generic measures of health-related quality-of-life.
Table 10
Disease-specific health-related quality-of-life in subjects with bilateral simultaneous cochlear implant.
Sequential Bilateral versus Unilateral Cochlear Implantation
Evidence was rated low based on data from two studies in four publications that were graded methodological quality-B. While a randomized controlled trial and a cross-sectional study showed benefit in speech perception in noise from sequential bilateral cochlear implants, a cross-sectional study did not find similar benefit in speech perception tests, both in noise and quiet conditions. In a randomized controlled trial evaluating sequential bilateral cochlear implants, the second ear implant resulted in negative results or non-significant changes in health-related quality-of-life after the first ear implant.
Study Characteristics
Five studies reported in eight publications (~ 208 subjects) compared sequential bilateral implantation with unilateral implantation.11, 51-53 One study conducted in the UK generated three reports, which had considerable overlap of participants. 51, 52 Another study conducted in Austria generated two reports with considerable overlap of subjects.53, 55 In the UK study, subjects were randomized to receive either immediate sequential second ear implant (1 month after first ear implant), or delayed second ear implant (9 months after first ear implant) with a prospective followup of 9 months.51, 52 The remaining studies were cross-sectional or retrospective in design and were conducted in the U.S.,11, 57 Switzerland,54 and in Austria.53 The U. S. study compared a small sample size of 13 subjects with bilateral sequential cochlear implants with subjects with unilateral cochlear implant (with or without hearing aid).11 The second U.S. study compared 22 subjects with bilateral implants to first ear implant. The Switzerland study compared 29 subjects with bilateral implants to either ear unilaterally. The Austrian study compared 18 subjects with bilateral cochlear implants with the unilateral implant use (right and left ear unilaterally).53 The mean age of included subjects with cochlear implant ranged from 46 to 60 years. The proportion of males included was 46 and 52 percent in three studies.11, 53, 57 Studies recruited subjects with severe to profound hearing loss for a mean duration of 6 to 32 years. Only one study reported the indication for cochlear implant; the subjects were required to have scores ≤ 30 percent open-set sentence recognition with BKB-SIN in quiet.52 The cochlear implants used were Nucleus® CI-24 implant system,51, 52 MED-EL COMBI 40/40+,53 and Advanced Bionics.57 Studies were graded quality-B 51, 52, 57 or were graded quality-C.11, 53, 54 In general, the studies of sequential bilateral cochlear implants had considerable differences in methodologies including duration of deafness, implanted devices, speech coding strategies, and tests for evaluation (Appendix Table D8 – D9).
Study Results
Speech perception with open-set sentences tests
In the Ramsden 2005 study of subjects with sequential bilateral cochlear implants, no significant advantage over the first (unilateral) ear was observed with the CUNY test in quiet at 3 and 9 months of followup.52 However, speech perception was better with CUNY test in noise for bilateral cochlear implants, and their scores were better than the first ear scores both at 3 and 9 months of followup. In one cross-sectional study (Gifford 2008) that compared bilateral sequential cochlear implants with unilateral or bimodal cochlear implant, group means of both BKB-SIN in noise and AzBio sentence recognition in quiet were not significantly different.11 However, in contrast to the BKB-SIN sentence recognition in noise results, the HINT sentences in quiet showed significant benefits with bilateral cochlear implants, where 28 percent of the subjects achieved 100 percent correct (P<0.001) HINT scores. This study did not report testing of HINT sentences in noise conditions. Schleich 2004 evaluated the SRT in 18 of 21 enrolled subjects with sequential bilateral cochlear implants using an adaptive signal to noise ratio (SNR) to minimize floor and ceiling effects with Oldenburg (OLSA) sentence test.
Table 11
Open-set sentences tests in subjects with bilateral sequential cochlear implant.
Additional outcomes of binaural processing
In Schleich 2004, comparing bilateral implants with each ear implant unilaterally, when averaged across listening conditions and noise conditions, there was a statistically significant head shadow effect of 6.6 dB, binaural squelch effect of 1.1 dB, and binaural summation of 1 dB.53 However, the binaural squelch effect was not significant for the comparisons of bilateral implant versus right ear unilaterally. Laske 2009 reported a statistically significant benefit for the head shadow effect when the sound source was from the activated side. For the OLSA test in quiet, the speech perception performance at 65 dB SPL was better by 18 percent in bilateral versus unilateral listening conditions. While for squelch and summation effects, results for the bilateral listening conditions were better for comparison with the unilateral better ear, but were not statistically significant.
Sound localization
Substantial significant benefits for bilateral implants versus unilateral listening conditions were reported in three studies.54-56 Two studies reported greater difference between bilateral and unilateral conditions, with a unilateral localization accuracy in the range of 50 to 67 degrees versus bilateral accuracy of 24 to 29 degrees. 55, 56 One study reported that the bilateral implants had a mean deviation from the actual sound source of 57 degrees. 54
Health-related quality-of-life
Five different instruments were used to assess the generic quality-of-life in a randomized controlled trial (Summerfield 2006) of 28 subjects with a unilateral cochlear implant;51 these included the Glasgow Health Status Inventory (GHSI), Health Utilities Index Mark III (HUI3), Visual Analogue Scale (VAS), EQ5D™ self-reported questionnaire, and tinnitus questionnaire (Table 12). Results from the first (unilateral) ear cochlear implant were compared with results following bilateral sequential cochlear implants at 3 and 9 months. In addition, these subjects (postsecond cochlear implant) were compared with unilateral cochlear implant recipients from the UKCISG. Significant gains were noted in the bilateral cochlear implant group compared with first (unilateral) ear cochlear implant group at 9 months in the GHSI quality-of-life measure. The HUI3 measure showed no change, the VAS showed non-significant but a negative change, and EQ5D showed significant negative changes following bilateral cochlear implant. However, in multivariate analysis negative scores after a second cochlear implant were associated with worsening of tinnitus, while positive changes in health-related quality-of-life were associated with improvement in hearing. To evaluate the issue of worsening of tinnitus, bilateral cochlear implants were compared with unilateral implant from the UKCISG (a cohort recruited for another study) and this comparison resulted in inconclusive results. The authors concluded that a second cochlear implant resulted in non-significant changes in measures of health-related quality-of-life.
Table 12
Health-related quality-of-life in subjects with bilateral sequential cochlear implant.
Bilateral cochlear (both sequential and simultaneous) versus Unilateral Cochlear Implantation
One study published from Switzerland included 37 subjects with bilateral simultaneous cochlear implant (N = 22) or bilateral sequential cochlear implant (N = 15).58 All subjects had progressive hearing loss with a mean duration of 11 years; mean age at bilateral cochlear implantation was 46 years. All subjects underwent Nucleus® 24 cochlear implantation. Speech perception was tested using two open-set sentences in quiet and noise – Hochmair-Schulz-Moser (HSM) sentences and the OLSA sentence test. Based on their performance at 3 and 6 months, either ear was classified as poorer or better performing at the 3 month test interval. Bilateral cochlear implants were compared with poorer or better performing ears again at 6 months. There was a significant bilateral benefit with significant mean improvement in performance in noise conditions for both HSM and OLSA, a further indication that there was the bilateral head-shadow benefit. When tested in noise conditions for OLSA, bilateral cochlear implant benefit was significantly greater when the better ear was closest to the source of speech (-11.4 dB) than when the poorer ear was closest to the source of speech (-10 dB). However, in quiet conditions bilateral cochlear implants showed benefit over the poorer ear only. While binaural squelch effect was marginally significant with HSM sentences (speech scores had significant improvement of 8% relative to the better ear alone, P = 0.02), binaural squelch effect was not significant for OLSA sentences in noise. Only a subgroup of 16 subjects had sound localization data assessed that showed binaural localization was significantly better compared with monoaural localization (each ear unilaterally). Bilateral implants had a 50 degree mean error compared with a mean of 90 degrees using unilateral implant only. This study did not evaluate health-related quality-of-life. The second study Cullington 2010 evaluated bilateral implantation with bimodal group. The results are further discussed in that section. 60
Bilateral Cochlear Implantation versus Bimodal (unilateral cochlear implant and an acoustic hearing aid)
Speech perception measures
Three quality-C studies (total of 119 subjects) evaluated bilateral cochlear implants compared with bimodal groups. Of these, two studies reported no difference between the two groups for speech perception measures of HINT sentences in noise and quiet, AzBio, and BKB-SIN.11, 59 One study noted significant differences in health-related quality-of-life of HHIE and HHQ in the bilateral group versus bimodal group. 45
Key Question 3a and 3b
- 3a.
What are the preoperative patient characteristics associated with the successful attainment of the communication-related health outcomes as well as quality-of-life outcomes in questions 2 or 3 in individuals ≥ 18 years of age who undergo simultaneous bilateral cochlear implantation?
- 3b.
What are the preoperative patient characteristics associated with the successful attainment of the communication-related health outcomes as well as quality-of-life outcomes in questions 2 or 3 in individuals ≥ 18 years of age who undergo sequential bilateral cochlear implantation?
At a minimum, the evidence surrounding the following will be discussed:
- Speech recognition/word understanding
- Auditory sensitivity/audibility
- Duration of impaired hearing
- Associated ear or bone diseases
- Pre vs. postlinguistic deafness
- Presence of other disabilities (e.g. visual impairment, impending or current)
- Age at implantation
- Degree of preimplant residual hearing
- Choice of implanted ear
- Site (expertise) of cochlear implant team
- Implanted device
Preimplantation Characteristics as Predictors of Postimplantation Outcomes
Evidence was rated low based on two quality-B rated studies reporting data on age at implantation as predictor of postoperative outcomes. The first study reported that a preoperative characteristic such as age at implantation (≤ 59 years of age) was predictive of different postoperative outcomes evaluated in these studies. The second study did not find an association between age at second implant and postoperative outcomes. Duration of hearing loss before implantation (two quality-B studies) and implant device characteristics (one quality-B study) did not predict postoperative outcomes.
Age at implantation
One quality-B study evaluated the association of adult implant age on sound localization and quality-of-life measures using the HHIE, and HHQ.60 The study was conducted as both prospective and retrospective. This study excluded implants followed retrospectively for >100 months, as these subjects had lower disability and handicap scores. The study participants overlapped with one study included under the section of bilateral simultaneous cochlear implantation.45 The study compared younger and older cohorts in the unilateral implants, bilateral implants, and bimodal groups. There were no significant differences between the two age groups among the unilateral implants, bilateral implants, and bimodal groups for the outcomes of sound localization and quality-of-life measures. However, differences in scores of quality-of-life measures using the preimplant to postimplant change were correlated with chronological age, younger adults (≤ 59 years of age) with bilateral implants had significant increases in both performance and self-rated abilities than the older adults with bilateral implants. In the unilateral implant group, there were no significant correlations between chronological age and preimplant to postimplant change quality-of-life measures. In both bilateral and unilateral groups there were no significant correlations between chronological age and preimplant to postimplant change sound localization. Another quality-B study (Zeitler 2008) did not find any relationship between subject error patterns in sound localization and age at second implant.57
Implanted device
One quality-B study evaluated the role of implanted device on speech perception measure of HINT.42 Twenty bilateral cochlear implants with an average use of 71 months were matched to 20 unilateral cochlear implants with an average use of 128 months on the following variables: age at implantation, duration of deafness, and type of internal device. The study reported that the bilateral implant group performed better compared to the unilateral group, indicating that implanted hardware had no role in the difference between the study groups.
Duration of impaired hearing
Two quality-B studies reported that there was no association between the duration of impaired hearing in the preoperative period with the postoperative performance in bilateral implant users.50, 57
Other Predictors
Laske 2009 reported that a short interval between implantations yielded better results for the second implant with an improved performance in the Oldenburger test in quiet.54 In addition Litovsky 2009 found that better sound localization was associated with binaural advantage in speech performance measures.49
Key Question 3c
Report the available evidence separately for those individuals with sensorineural hearing loss as demonstrated by test scores of > 40 percent and ≤ 50 percent, as well as those with test scores between > 50 percent and ≤ 60 percent (best aided listening on tape or otherwise recorded tests of open-set sentence recognition).
Overall, evidence was rated low for the effectiveness of simultaneous bilateral implantation by their preimplantation open-set sentence test scores of ≤ 40 percent, which was evaluated in three quality-B studies that showed improved speech perception and sound localization, but inconsistent gains in terms of hearing-specific quality-of-life in one study. There was lack of information on the percentage of subjects with preimplantation scores of > 40 percent and ≤ 50 percent. No studies reported data on the preimplantation scores of > 50 percent and ≤ 60 percent among bilateral implants. Evidence was rated insufficient for the effectiveness of sequential bilateral implantation by the preimplantation test scores of ≤ 40 percent, which was evaluated in one quality-B study that showed improved speech perception in noise, and sound localization.
Two studies of simultaneous bilateral implants conducted in the U.S. reported the requirement of an open-set sentence score of ≤ 50 percent in the best-aided condition as an indication for bilateral cochlear implantation.43, 44 Koch 2009 reported that the bilateral scores for the HINT in quiet was greater than the left ear alone (between 3 and 8 months, P < 0.05) and greater than the right ear alone (between 6 and 8 months, P < 0.05).41 All subjects in this study localized sounds better with two implants compared with either implant unilaterally, and had a head shadow advantage for all test conditions. However, the binaural squelch effect was small with only 7 of the 15 subjects showing a squelch effect for at least one of the noise-right or noise-left conditions. The second study (Litovsky 2006) examined BKB-SIN test results in nine test conditions, which included three listening conditions and three noise locations.44 A bilateral listening condition was better than either ear unilaterally at 3 and 6 month intervals. Between 3 and 6 months, an overall improvement in BKB-SIN test performance occurred under most of the listening conditions as well as most of the noise locations, suggesting that bilateral implantation aided participants to overcome the “head shadow effect” when in noise. The reduction of speech perception by the “head shadow effect” is amplified in the presence of background noise. However in this study, noise from the frontal location (0° azimuth) resulted in a significantly poorer performance than when the noise was from either side of the head.
Two additional studies included subjects who had a preoperative open-set sentence score of minimum 30 or ≤ 40 percent in the best-aided condition as an indication for bilateral cochlear implantations.46, 52 Buss 2009 reported binaural benefits in derived measures of head shadow effect, squelch, and summation during 1 year followup. While SNR values decreased between an interval of 3 months to 6 months, this did not reach statistical significance; of note, SNR values decreased significantly between an interval of 6 months and 1 year.46 In the Ramsden 2005 subjects with a minimum 30 percent open-set speech recognition in the first ear underwent sequential second ear implant. This study reported that no significant advantage over the first (unilateral) ear was observed with the CUNY test in quiet at 3 and 9 months of followup.52 However, speech perception was better with CUNY test in noise for bilateral cochlear implants, and their scores were better than the first ear scores both at 3 and 9 months of followup. In this cohort of subjects, published in a different study, the second ear implant resulted in negative results or non-significant changes in health-related quality-of-life after the first ear implant.
Discontinued use of Cochlear Implant
In total, 20 subjects across all groups were reported in four studies to have adverse events and details of these events are summarized in the Appendix Table.D5. In summary, where adverse event data were available, 20 out of 495 subjects (4.0 percent) discontinued use of their cochlear implant(s) after hearing-related complications.
Nine (4.2 percent) patients implanted in the series became permanent non-users: three due to exacerbation of co-existing illness, and two due to a worsening of their tinnitus postimplantation; one patient declined preimplantation following a device failure and one patient who initially had a successful implant outcome has been advised against reimplantation following device extrusion in a previously irradiated temporal bone; two patients elected not to use their device with the reason given being disappointment with the outcome from their implantation. 17 One out of 34 subjects had a cerebrovascular accident 5 years postimplantation that caused sudden and permanent inability to hear with implantation. 20 One bilaterally-implanted patient out of 30 discontinued use of a single implant after inability to integrate separate signals from each ear. 52 Three adult patients out of 251 became non-users with reasons listed including depression, tinnitus, concomitant neurological problems, and non-auditory stimulation. 61
New Technologies: Hybrid implantation
We identified one prospective clinical trial of 87 subjects implanted unilaterally with Nucleus® hybrid devices.62 This study was rated quality-C. The study tested a subgroup of 27 subjects with Hybrid implantation using spondee recognition in multitalker babble for speech reception threshold values, which were plotted as a function of their pure tone acoustic thresholds of 125, 250, and 500 Hz.62 Subjects displayed speech recognition in noise when residual hearing was preserved to levels no worse than severe hearing loss and when there was preservation of low frequency acoustic hearing in the postimplantation period. This study reported two subjects with total hearing loss within the first month of cochlear implantation. In this study, the indication for cochlear implantation was the Consonant-Nucleus-Consonant word scores of 10 to 60 percent in the preimplant ear and up to 80 percent in the contralateral ear.62 The study did not assess any predictors of postoperative outcomes of open-set sentences or multi-syllable tests. This study did not evaluate quality-of-life outcomes.
- Results - Effectiveness of Cochlear Implants in Adults with Sensorineural Hearin...Results - Effectiveness of Cochlear Implants in Adults with Sensorineural Hearing Loss
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