Electric acoustic stimulation

Electric acoustic stimulation (EAS) is the use of a hearing aid and a cochlear implant together in the same ear. The hearing aid acoustically amplifies low frequencies, while the cochlear implant electrically stimulates the middle and high frequencies. The inner ear processes acoustic and electric stimuli simultaneously.

The results of international studies have shown a highly synergistic effect between hearing aid and cochlear implant technology, particularly evident in speech understanding in noise, pitch discrimination and music appreciation.

Electric stimulation of the auditory system via cochlear implant is a commonly used technique for individuals with a severe to profound sensorineural hearing loss, as well as for those adults and children with some residual hearing.

Individuals suffering from mild to moderate hearing loss can usually benefit from hearing aids. This acoustic stimulation proves to be particularly effective in the low frequencies, though a severe hearing loss (> 70 dB HL) above 1 kHz can be beyond the range of amplification possible via acoustic stimulation. Electric stimulation (CI), on the other hand, is capable of providing high-frequency information up to 8 kHz.

The concept of combining simultaneous electric-acoustic stimulation (EAS) for the purposes of better hearing was first described by C. von Ilberg and J. Kiefer, from the Universitätsklinik Frankfurt, Germany, in 1999. That same year the first EAS patient was implanted.

There is a certain patient group that has some degree of residual hearing in the low frequencies and a severe hearing loss in the high frequencies. This group only receives limited benefits from traditional amplification because of the severity of the hearing loss in the high frequencies. They suffer from inadequate speech comprehension, even in the best aided condition. Nor are they classic cochlear implant candidates, because of their mostly intact low frequency residual hearing.

The indications for EAS are based on the following three considerations:

below 1.5 kHz – No or moderate HL

above 1.5 kHz – Severe to profound sensorineural hearing impairment

The patient's monosyllable word score should be ≤ 60% at 65 dB SPL in the best aided condition.

Contraindicated are:

A special surgical technique is the key to preserving the residual hearing of the patient. In most routine cochlear implant surgeries, any residual hearing will likely be destroyed.

Important factors for preserving residual hearing are:

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