Thoughts about Unilateral Hearing, Unilateral Cochlear Implantation,
and Bilateral Cochlear Implantation
During the early days of cochlear implantation, the procedure was performed in one ear only. Some users continued using their hearing aid in the non-implanted ear, sometimes with little benefit. Some CI users even noted that that their hearing aid might be interfering to some degree with their speech understanding but continued to use amplification to keep their residual hearing active in the event that they were able to benefit from future technology.
Growing awareness of the disadvantages of unilateral hearing loss and the benefits of bilateral hearing led, to two important changes relative to cochlear implantation:
- Bilateral implantation became a rehabilitative path chosen more for both adults and children;
- Criteria for implantation expanded to include people with some functional hearing in the non-implanted ear (e.g., moderate to severe hearing loss with some open set speech recognition).
Appropriate candidates benefit from the advantages of bilateral hearing when using a conventional hearing aid in one ear and CI in the other. We'll talk about this topic in another upcoming blog post.
This blog post is directed mainly to those who have one CI—either those who do not use a hearing aid in the contralateral ear or those who use a hearing aid in the other ear but derive minimal benefit. Unilateral hearing should be considered in the context of the following questions:
- What are the disadvantages of unilateral hearing?
- What are the benefits of bilateral cochlear implantation?
- When should someone choose to "go" bilateral?
The answer to the last question should be made on a case-by-case basis considering factors such as functional hearing in the non-implanted ear, years of hearing deprivation, and the person’s age. There is no conclusive answer that applies for all individuals. However, we can discuss the different effects of unilateral hearing on communication function as well as the advantages of bilateral cochlear implantation.
There is no doubt that unilateral CI can significantly contribute to one's auditory skills and quality of life. Many environmental sounds and speech sounds become accessible for unilateral CI users and a significant improvement is usually experienced in speech perception, especially in quiet conditions.
We have learned from those with normal hearing in one ear and hearing loss in the other ear, as well as the experience of people using one cochlear implant, that unilateral hearing imposes limitations for various situations in everyday life. Children with single-sided deafness, who have normal hearing in one ear, are at risk for lower language performance as well as social and academic difficulties. Many of these children report fatigue during class and difficulties in coping with school requirements. Adults with single-sided deafness may also experience difficulty in social settings, inattentiveness, stress, and headaches. Evaluations of people with normal bilateral hearing point that hearing with two ears contributes significantly to speech understanding, especially when listening to speech in noisy environments.
The challenges of unilateral hearing are due to reduced auditory ability in the following types of situations:
- Speech is directed to the side of the "poor" ear;
- Individual has difficulty knowing the speaker’s location to aide speechreading;
- Detection and understanding of soft sounds as two ears provide “redundancy”;
- Understanding speech in noisy situations.
Unilateral CI users often report on similar difficulties. Yet we cannot consider single-sided deaf individuals and those with bilateral hearing loss with one CI as one and the same because a cochlear implant does not provide normal hearing. Therefore, the difficulties of unilateral CI users are typically greater compared to those of people with normal hearing in one ear.
These considerations are at the heart of why we should closely examine the potential benefits bilateral cochlear implantation for everyone. So, what can we learn from the literature? We find research focusing on adults' auditory function with one CI versus two CI's (i.e., how their function changed with a second CI). We can also find research comparing the function of adults who have unilateral CI with adults who have bilateral CI. A review of 20 studies* highlights the following key findings:
- Speech perception in quiet. There are no consistent findings of bilateral advantage over unilateral CI use.
- Speech perception in noise. Studies consistently demonstrate the benefit of two cochlear implants over one and these advantages increase as the acoustic conditions worsen.
- Localization. Studies demonstrate the benefits of bilateral hearing to identify the location of a speaker or environmental sounds.
- Daily activities and quality of life. Self-reported questionnaires found bilateral CI benefits for spatial hearing, ease of listening, quality and clarity of sounds, and social interactions. These findings suggest that bilateral cochlear implantation has real potential to enhance communication and orientation, reflected in various daily situations, and thereby improving quality of life.
As is the case for an initial cochlear implant, the decision on a second CI is affected by various parameters beyond the patient's motivation to take another step towards better hearing. There are pros and cons that are unique to each person. If you wish to consider a second cochlear implant, the recommended first step is to consult with your CI team. Realistic expectations are important. While there is the potential for quality of life improvements, it is important to recognize that bilateral CI will still not provide normal hearing. Further, one must consider that there are rehabilitation requirements in order to maximize outcomes with the second CI and that this is essential to your success!
*Van Schoonhoven J, Sparreboom M, van Zanten BG, Scholten RJ, Mylanus EA, Dreschler WA, Grolman W, Maat B (2013). The Effectiveness of Bilateral Cochlear Implants for Severe-to-Profound Deafness in Adults: A Systematic Review. Otology & Neurotology, 34 (2), 190-198.
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