OTOACOUSTIC EMISSIONS - A NEW METHOD TO DIAGNOSE HEARING IMPAIRMENT IN CHILDREN

Otoacoustic emissions (OAEs) are epiphenomena of sensitive, amplifying processes during hearing which can be detected in persons with normal inner ear function. They originate from the cochlea and are interpreted as an energy leakage of cochlear processes, perhaps resulting from active outer hair cell movements. OAEs travel from the cochlea through the middle ear to the external auditory canal where they can be detected using sensitive miniature microphones. Transient evoked (TEOAE) tests allow to otoacoustic emissions non-invasively check the integrity of the cochlea. In the neonatal period, registration of OAEs can be accomplished during natural sleep. In infants and neonates TEOAEs can be used as screening test with a screening level at 30 dB HL in paediatric audiology. They are less time consuming and elaborate than auditory brainstem responses (ABR) and they are more sensitive than behavioral tests. TEOAEs are constant over long periods of time and they are reduced or absent due to various adverse influences in the inner ear. These latter characteristics may allow monitoring of the inner ear function over time e.g. during disease and/or during ototoxic therapeutic interventions. Limitations of this new method are due to the fact that TEOAEs are absent in patients with a more than 30 dB HL hearing loss. Thus a hearing threshold cannot be determined. Diseases of the inner ear which are common in early childhood (like otitis media) reduce the transfer of TEOAEs and may wrongly indicate a cochlear hearing disorder. New methods for evaluation and interpretation of TEOAE test results are currently developed which may allow to circumvent this problem. When used by an experienced examiner who is aware of the possibilities as well as of the limitations of this new method, registration of TEOAEs is a promising new tool which complements our current-armamentarium to diagnose hearing disorders in children.