The World Health Organization1 estimates that disabling hearing loss affects some 5.3% of the world’s population, or some 360 million individuals. Of these, 32 million are children under 15 years of age, many with congenital hearing losses. It has been well established that hearing loss can have significant impact on an individual’s participation in their community, affecting educational, employment, and social interactions, particularly in the case of children. In most developed countries, with an ageing population, the prevalence of age-related hearing impairment is also increasing. Recent evidence points to an important association between hearing loss and cognitive decline in the elderly.
Advances in hearing aid technology worldwide have led to improved functional outcomes for hearing-aid users; however, there remains a large proportion of children and adults for whom hearing aids are not sufficient to provide the sophisticated auditory ability so necessary in the modern world. For these individuals, the advent of multichannel cochlear implants has provided a revolutionary change in prospects, enabling children born with profound hearing loss to develop near-normal speech and language, and, in most adults, significantly surpassing pre-implant communication abilities.
In 1985, the University of Melbourne’s Department of Otolaryngology, led by Professor Graeme Clark AC, joined with the Royal Victorian Eye and Ear Hospital (RVEEH) to establish Australia’s first public hospital Cochlear Implant Clinic. From its inception, the Cochlear Implant Clinic and the University of Melbourne have worked closely with Cochlear Limited in the development and clinical evaluation of successive generations of the Nucleus cochlear implant system. In 1992, this collaboration was expanded, through the establishment of the HEARing Cooperative Research Centre. The HEARing CRC is a consortium of 24 member organizations that brings together universities, the hearing healthcare industry, government services and research providers, clinical agencies and hospitals, early intervention centres, and professional audiology associations. All partners are focused on the twin challenges of more effective prevention and improved remediation of hearing loss.
These partnerships have enabled a broad range of studies to be undertaken, many of which have led to new designs of cochlear implant electrode array and improved speech processing technology. The impact of successive improvements in technology has been the expansion of candidature for cochlear implantation. Since the implantation of Rod Saunders, the first patient to receive an experimental cochlear implant in Melbourne in 1978, the inclusion criteria for cochlear implant candidature has steadily expanded from that of total hearing loss to the current practice of cochlear implantation as routine in patients with significant residual acoustic hearing thresholds, and increasing use in some patients with single-sided deafness. Further, cochlear implantation is being recommended for candidates ranging in age across the spectrum, from infancy through to the very elderly.
To address this expanded candidate population, manufacturers have developed a range of cochlear implant systems, with electrode arrays developed specifically for hearing preservation, improved speech processors and speech processing strategies to enhance hearing in noise, and the option of combining electric and acoustic hearing in the implanted or contralateral ear.
The clinical recommendation for any specific individual on their candidature for a cochlear implant is based on a broad range of surgical, medical, audiological, and social assessments. In making recommendations on candidature, the clinician is reliant on guidelines established by regulatory authorities, information provided by the manufacturers, and, most critically, evidence on outcomes from the research and clinical literature.
Given the rapidly expanding criteria for cochlear implant candidature, it is imperative that clinicians have access to an evidence-base of outcomes with cochlear implants to guide clinical decisions for the wide range of potential clients. This special supplement presents a series of papers providing evidence-based guidelines for recommending cochlear implants across a range of clients. The studies capitalize on the long-term clinical experience of The University of Melbourne / RVEEH Cochlear Implant Clinic and clinical research studies conducted through the HEARing CRC. In each of the articles, the authors provide information to clinicians to assist them in making recommendations of the potential for their adult and paediatric clients to benefit from cochlear implantation. We hope that this special issue will provide new insights into barriers to, and facilitators of, successful cochlear implant outcomes. As per standard procedures for the International Journal of Audiology, all submissions were peer-reviewed by external reviewers prior to being accepted for publication.
The first group of papers in this special issue present evidence-based approaches to making recommendations for cochlear implantation in specific patient segments. The first paper, Leigh et al (a), presents a framework for clinical recommendations for cochlear implant candidature in adults, based on long-term experience and evaluation of outcomes. In the second paper, Leigh et al (b), the focus shifts to audiological criteria for recommendations in paediatric clients, with a special emphasis on optimizing the age at implantation. The topical issue of cochlear implantation in adults with long durations of monaural sound deprivation is addressed by Boisvert et al (a) in the third paper. In the final paper of this group, Rousset et al give insight into recommendations for outcomes in adults with prelingual deafness, a group characterized by widely varying outcomes.
As noted already, cochlear implant candidature has been expanded through the advent of bilateral cochlear implantation as standard clinical practice, as well as options for use of combined acoustic and electric input. In the first of the papers addressing this aspect, Plant et al present information on the benefits of combining acoustic hearing and electrical stimulation in adult patients. The issue of benefits of bilateral cochlear implant fitting in adults over 50 years of age is addressed by Boisvert et al (b). Fitting of a combined hearing aid and cochlear implant is assumed to be an important aspect of patient satisfaction and outcomes, and experience with use of the NAL-NL2 prescription for fitting the acoustic component of a combined electro-acoustic fitting is explored by English et al.
The final group of papers focuses on how we can optimize long-term outcomes of cochlear implantation for different client populations. For adults, Richard Dowell presents evidence drawn from long-term studies supporting the case for earlier cochlear implantation in postlingually deafened adults. While outcomes primarily focus on restoring spoken language and communication, the ability to enjoy music is a limitation often noted by cochlear implant recipients. This issue is addressed by Moran et al for both prelingual and postlingually deaf adult cochlear implant recipients. Results of a range of studies, including the HEARing CRC’s own Longitudinal Outcomes for Children with Hearing Loss study (featured in the International Journal of Audiology, volume 52, supplement S2, 2013) as well as studies by Sarant et al (2015) and Dettman et al (2016) from The University of Melbourne, have clearly established the potential benefit from early detection of hearing loss through universal newborn screening, coupled with early intervention including, where appropriate, cochlear implantation. In the third paper of this group, Dettman et al explore the barriers to early cochlear implantation in infants and children. While all of the studies noted thus far focus on audiological aspects of candidature, we are cognisant that surgical and medical considerations play an equally important role in determining candidature. To complete the consideration of paediatric cochlear implantation, Wasson and Briggs summarize contemporary issues in paediatric cochlear implantation.
The special supplement is closed out with an Epilogue from Richard Dowell, whose wealth of clinical experience flows from his involvement with the very first Melbourne CI Clinic patients continuously through to leading today’s RVEEH Cochlear Implant Clinic.
Together with Richard, the Guest Editors of this special issue have been involved in cochlear implant research and clinical practice over the past three decades. From the first patients, in whom the initial prognosis was for a benefit to lipreading from cochlear implantation, we have seen continuing developments in the field, with new technology and clinical practice providing the potential for restored communication in adult clients, as well as the development of peer equivalent speech and language in congenitally deaf children. However, clinicians working in the field will be aware that, while these outcomes are achieved by a majority of clients, there remains a wide variance in functional results. It is imperative that clinicians are aware of the evidence-base of known factors associated with outcomes of cochlear implantation for different patient populations to assist them in making clinical recommendations.
This special issue, and the growing evidence-base for the recommendations as presented, would not have been possible without our cochlear implant recipients, who have all given generously of their time to participate in research and clinical studies. The editors would like to dedicate this special edition to our clients, and hope that their contributions will ultimately lead to improved outcomes.
We are also grateful for the continuing support of The University of Melbourne’s Department of Audiology and Speech Pathology, The Royal Victorian Eye and Ear Hospital Cochlear Implant Clinic, the Sydney Cochlear Implant Clinic (a division of The Royal Institute for Deaf and Blind Children), Macquarie University’s Department of Audiology, Cochlear Limited, and the HEARing Cooperative Research Centre, each of which has contributed to the studies presented in this special issue.
Robert Cowan, Karyn Galvin, Richard Dowell
May 2016
Acknowledgements
The publication of this special supplement to the International Journal of Audiology has been made possible through the generous funding support of the HEARing CRC Ltd, established and supported through the Australian Government’s Business Cooperative Research Centres Programme.
Note
1. World Health Organization, Millions Live with Hearing Loss, 2013.
