An Overview of Cochlear and Related Implant Technology
The cochlear implant in its current form took many years to develop and the earliest attempts to test amounts to a bionic ear began with the first human trials in 1957. At first, efforts were fraught with failures and abandoned research projects that inevitably delayed the production of an effective solution for the profoundly deaf. It was a further 21 years before reproducible results were obtained, encouraging other researchers to introduce the various refinements that were to culminate in the devices now used to restore the lifestyles of many thousands of subjects for whom the use of a conventional hearing aid would have been ineffective.
For simplicity, the cochlear implant can be thought of as a means to bypass the normal but compromised route by which sound reaches the inner ear, in much the same way as a motorist may use back roads to avoid a rush-hour traffic jam on the highway. Sound is captured by tiny but powerful external microphones, amplified and passed to a combination speech processor and transmitter located behind the ear. A receiver beneath the skin converts the digital sound signal to electrical pulses and forms one end of the “electronic bypass”. At the other end, an array of electrodes is positioned within the cochlea, where it stimulates the auditory nerve directly.
Actually, the cochlear implant does not reproduce sounds in quite the same way that they are heard naturally. However, with a little professional coaching and practice, subjects may be fully rehabilitated and resume a normal lifestyle in which little or no evidence of any impairment will be apparent. Interestingly, among medical prostheses, these devices are undoubtedly the most successful with no more than half of one percent requiring re-implantation and far less than that resulting in rejection. Typically they are recommended in cases of profound, bilateral sensorineural impairment, where the auditory nerve remains functional. Although infants are also eligible, rehabilitation is quicker for those already capable of speech.
The success of the cochlear implant has been accompanied by the development of a number of related bypass devices that also require surgical implantation but are suited for use in differing clinical circumstances. For those with problems in the middle or outer ear that obstruct the conduction of sound, a bone anchored hearing aid (BAHA) could be the solution. A device located in the bone behind the ear connects to the external processor, converting sounds to physical vibrations within the bone, which can then stimulate a healthy cochlea directly, bypassing the normal conductive pathway.
Middle-ear implants work similarly, but the vibrating component is attached near the cochlear window or to one of the tiny bones located in the middle ear. They are a useful option for those with a narrow or collapsed ear canal, subjects who experience allergies to ear-moulds of conventional hearing aids and patients who suffer recurrent ear infections.
In the past, no solution for those with a non-functional auditory nerve was available but, today, this is no longer the case. Differing from the devices in which an electrode array acts on the cochlea, the auditory brainstem device employs an array located within the brainstem.
Assisted hearing technology has attained new heights and promises hope for many who, before cochlear and similar implants, had none.