Severe to Profound Loss in Both ears? Cochlear Implant in one ear OR two ears?
Cochlear implant (CI) is a surgically implanted neuro-prosthetic that provides a person with severe sensori neural hearing loss a modified sense of sound. CI bypasses the normal acoustic hearing process to replace it with electric signals which directly stimulate the auditory nerve. A person with a cochlear implant receiving intensive auditory training may learn to interpret those signals as sound and speech. In India most of the children or adults who needs cochlear implant are undergoing unilateral cochlear implantation. Although unilateral cochlear implantationgenerally provides good speech understanding under quiet conditions, cochlear implantation patients frequently report difficulty understanding speech when exposed to background noise and with sound localization. Since these two listening functions require binaural stimulation for normal individuals, it is not surprising that there is growing interest in binaural implants.
Bilateral implantation may be an option for individuals who are cochlear implant (CI) candidates or current CI recipients who already have one ear implanted. There are two options for bilateral cochlear implantation:
- Simultaneous implantation - both ears are implanted in the same surgery. With this option, patients only have to be in the hospital once and only go under anaesthesia once. This option is much less expensive than having two separate surgeries. Simultaneous implantation is a particularly good option for individuals recently deafened by meningitis because the disease can cause bone to grow and fill in the cochlea, which can make it extremely difficult or impossible for an implant to be inserted at a later date.
- Sequential implantation - the CIs are placed during two separate surgeries. The time interval between the first and second surgery can range from weeks to years. This option is common for individuals who received their first CI years ago and would like to experience binaural hearing and/or benefit from newer technology in the second ear. This option is also common for people who don't want to be completely without sound or "off the air" for any length of time.
Why Should I Consider Bilateral Cochlear Implantation?
- Hearing is normally accomplished with two ears. We are born with two ears and our brains are wired to receive input from both ears. It is the standard of practice in audiology to provide hearing aids for both ears, so it has been suggested that it should also be the standard of practice to provide two CIs.
- Better localization and understanding speech in noise. Having two ears allows us to determine where sounds come from (localization), and it helps with understanding speech in background noise. Current research on bilateral cochlear implantation has shown a wide range in recipients' performance on these two particular tasks. In general, bilateral CI recipients tend to be able to localize better and understand speech in noise better with two CIs than with one. India is a crowded place and the traffic noise is also more than permitted levels, being in these situations bilateral implantation will give more than 40% benefit.
- Better sound quality, less listening effort, and other benefits. Benefits of bilateral implants appear to extend beyond sound localization and hearing in noise. Many bilateral implant recipients report better sound quality/clarity, more acoustical balance, greater ease in following group conversations, and less fatigue at the end of the day. In common language, when you work with two hands and one hand comfort levels are different, same way when you listen with both the ears hearing clarity will make that difference. Recent research finding suggested that children with two CIs are much more confident to engage in group conversation and to stay in those conversations. This has very important implications for socialization in hearing impaired children. Additionally, parents report improvements in their child's behaviour with bilateral CIs.
- Never being without sound. In the unfortunate event that external equipment breaks (e.g., a cord, processor, headset) or the internal device fails, having a second implant means that the recipient never has to go without sound. This is an important consideration for adults who cannot afford to miss work because they can't hear or for children who would otherwise miss out on learning opportunities in daily life or at school.
What are the Potential Disadvantages of Bilateral Cochlear Implantation?
- Cost. In addition to the increased costs associated with surgery and a second device, the costs associated with maintaining hardware (cords, cables, batteries, speech processors, service agreements/extended warranties, etc.) is doubled with two CIs. There is also added cost for clinical services due to the extra time needed for programming two speech processors.
- Future technological advances. Some people want to "save" the other ear for future technological advances. One problem with this is that research has shown that lack of auditory input causes the neural pathways in the auditory system to slowly die back (atrophy). If the neurons atrophy, then the CI won't have much to stimulate and the recipient will get little benefit from the implant. Therefore, hearing aid use is highly recommended if an individual is considering waiting for implantation at a much later date.
Chief Audiologist & Clinical Specialist in Cochlear Implants
Shravya Speech & Hearing Center, Hyderabad
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