Current Status and Problems of Cochlear Implant

Abstract

At the present time there is no defined treatment for profound sensory hearing loss. Clinically, it is possible to stimulate the remaining auditory nerve fibers by electronic devices (cochlear implant) in order to restore hearing. This paper will give an outline of the current status of cochlear implant.The electronic devices that receive their input from a microphone/amplifier system and send their output to the implanted electrodes are classifed into the following three systems: 1) percutaneous transmission system, 2) transcutaneous transmission system, and 3) implantable package system. Two locations, the scala tympani and modiolus, are reported as suitable sites for cochlear implant. The scala tympani approach takes advantage of the cochlea's tonotopic organization to stimulate the auditory nerve fibers selectively, though it is limited by the current shunting in the cochlear fluid The modiolar approach permits access to the fibers coming from all parts of the cochlea, though selective stimulation of small groups of fibers is difficult. It is proved that a cochlear implant with a single channel system is useful only as an aid to lip reading and for distinguishing some environmental sounds. To improve speech discrimination, a multichannel system is indispensable, though it is unknown how many channels may be necessary in order to provide intelligible speech. The indication of the cochlear implant is assessed by the electrical promontory or round window stimulation test. The etiopathological backgrounds considered suitable for implantation are deafnesses caused by ototoxic drugs or head trauma, hereditary sensory deafness of adult onset, and advanced bilateral Meniere's disease.