Wednesday, December 26, 2001

Use of cochlear implants on the rise

Thousands of children and adults with very severe hearing loss have received cochlear implants in the past 25 years. Improvements in surgical techniques, aural rehabilitation methods and advances in the technology of the implant devices themselves have led to improved results in recent years.

As helpful as the cochlear implant can be, the procedure is not suitable for the vast majority of people with hearing loss. Candidates for a cochlear implant are usually people who, because of the severity of their hearing loss, receive little or no benefit from conventional hearing aids.

They may, however, benefit from stimulation of the auditory nerve when electrodes are surgically placed directly into the inner ear (cochlea). The cochlear implant also has a microphone and amplifier worn externally, and usually employs sophisticated digital processing to deliver the most effective signal to the cochlea.

Middle ear implants

Recently, the Food and Drug Administration approved for clinical trial several devices that are implanted into the middle ear. Several hundred people have received middle ear implants in the United States and Europe. These are people with less severe loss than those receiving the cochlear implant, with hearing loss ranging from mild to severe (30 to 75 dB HL).

Middle ear implantable hearing aids use either a piezoelectric crystal or an electromagnetic coil connected to one of the bones of the middle ear. A microphone and transducer, which look like a small hearing aid, are worn externally. Sound energy is amplified and then applied to the ossicular chain, which directs the amplified energy into the inner ear.

Cochlear and middle ear implants don't restore normal hearing and the individual still must use an amplification device similar to a hearing aid. A surgical procedure is required.

Pre-surgical and post-surgical audiologic evaluations, counseling, and programming of the instruments are critical parts of the process. Also, the cost is significant (about $15,000 for a middle ear implant and about $25,000 for a cochlear implant). Nevertheless, these procedures can provide important benefits for some people with hearing loss.

Andrew Waits

Clinical audiologist