Hearing about cochlear implants
Posted on 4 September 2012
Our expert is Dr Derrick Wagenfeld, an ear, nose and throat specialist based at Mediclinic Vergelegen in Somerset West.
Can anyone who is deaf benefit from a cochlear implant?
Anyone with sensorineural deafness, which results from damage to or incorrect functioning of the inner ear (cochlea), could benefit from a cochlear implant. Cochlear implants essentially replace the hair cells in the cochlea, which are responsible for changing the physical energy of a sound signal into an appropriate electrical signal in the auditory nerve. The auditory nerve then transmits the sound information to the brain. If your hearing loss is due to sound not being transmitted correctly through the ear canal and middle ear, however, a hearing aid is usually the best option.
How is a cochlear implant different from a hearing aid?
A hearing aid is a totally external device that amplifies the incoming sound signal to stimulate existing hair cells in the cochlea. A cochlear implant, however, actually bypasses the hair cells to deliver sound information directly to the auditory nerves. The implant system consists of two parts: an external sound processing unit and an internally implanted bundle of thin electrodes. The sound processor analyses the incoming sound and then encodes it according to a computer-generated algorithm. The signal is then transmitted to the internal part via a radio-frequency link, and the appropriate electrode is selected for stimulation based on the characteristics of the signal.
What does the surgery involve?
A small incision, about 5 cm long, is made behind the ear for placing the internal device. It is done under general anaesthesia and the functionality and neural response to stimulation is confirmed before the patient wakes. The procedure takes 2 – 3 hours and you should be able to leave the hospital within 24 hours. A follow-up visit to your doctor is necessary after 3 and 7 days, and activation of the implant follows 2 – 3 weeks after surgery. The cost of the device is about R200 000, depending on the exchange rate. The total medical costs are between R50 000 and R100 000, usually covered in full by most medical schemes.
What will my world sound like?
Cochlear implantees often report sound being somewhat electronic, different from what they remember things sounding like. The sound is often described as ‘tinny’ or ‘sounding like Donald Duck’. However, we hear with our brains and these fortunately are highly adaptable, so that by six months of use the sound usually becomes ‘normal’ to implant users. The younger the age of cochlear implantation, the more accustomed the brain will become to electronic signals and the more natural things are likely to sound. Nowadays people with profound hearing loss can receive cochlear implants in both ears, or an implant in one ear supported by a hearing aid in the other. This helps a lot with determining the direction from which sound comes and creates a fuller sound scene for the listener.
Will I be able to use the telephone and listen to music?
Over the past 30 years cochlear implant technology has improved greatly. Speech perception with the implant is excellent and nearly all patients who satisfy the criteria for surgery are able to converse well without lip reading. About 70% of our patients are able to use the telephone with ease. Music perception, however, is challenging and people report varying degrees of enjoyment. Rhythm is perceived well, but melodies can often not be recognised. This is because of the limited number of electrodes available, which means that the frequency resolution is not adequate for discerning small pitch changes as found in melodies. This is a field of intense research at this time.
If you’d like to know more about cochlear implants, post your questions here. You can also post it to www.facebook.com/MediclinicSouthernAfrica