A normally functioning cochlea produces inaudible measurable sounds called otoacoustic emissions (OAE) in response to external audible sounds. OAEs are the result of microscopic
biomechanical activity (motility) associated with healthy outer hair cells. This activity
produces a signal within the cochlea that is transmitted back through the middle ear and ear canal, where it can be picked up by a microphone. A probe placed in the ear canal can detect these vibrations. The presence of OAEs suggests that the peripheral auditory system up to and including the outer hair cells is functioning appropriately. Absence of OAEs is consistent with abnormal cochlear function or the presence of an outer/middle ear problem. Middle ear fluid or negative middle ear pressure, often characteristic of otitis media, can interfere with OAE measurements. As a result, a simultaneous tympanogram is needed in order to accurately interpret OAE data. OAEs are completed as a part of a diagnostic test battery and the results should not be interpreted in isolation. OAEs provide ear-specific and frequency- specific information that can assist with site of lesion determination and/or cross check against other results of the test battery. A condition known as auditory neuropathy can be diagnosed by comparing OAE results (typically normal) with ABR results (typically abnormal). OAEs are electrophysiologic, requiring no behavioral response from the pediatric patient. OAE testing is capable of detecting changes in the cochlea before hearing loss is noted on a behavioral audiogram and therefore it is often included in the audiologic test battery used for hearing sensitivity monitoring.
Two types of OAE tests are used clinically: transient evoked otoacoustic emission (TEOAEs) and distortion product otoacoustic emission (DPOAEs). TEOAEs are recorded in response to very abrupt (click or toneburst) stimuli. DPOAEs are responses generated when the ear is stimulated simultaneously by two pure tone frequencies.