Otoacoustic Emissions

The outer, middle, and inner ear are the three main parts of the ear. When it’s necessary to test how well the inner ear, or cochlea, is working, an audiologist may perform a test that evaluates otoacoustic emissions (OAEs), referring to sounds produced by the cochlea.

Cochlear sounds can also be used to evaluate hair cell function and test other structures affecting hearing, such as the auditory nerve.

In response to sound, the inner ear produces sounds called otoacoustic emissions. Specifically, it’s hair cells in the inner ear that vibrate in response to sound. These vibrations produce quiet or very low frequency sounds that echo into the middle ear. It’s these sound emissions that are measured when OAEs are tested. With normal hearing, these “quiet sounds” will be produced. But if hearing loss exceeds 25–30 decibels, OAEs will not be produced or detected. A lack of soft sound echoes can also suggest a blockage in the middle or outer ear.

OAE testing is usually recommended for newborns to look for signs of deafness. With babies, testing of this nature is often a part of a newborn hearing screening program. Otoacoustic emissions testing may also be done to get a better idea of a patient’s hearing sensitivity. In some instances, OAE testing is performed on patients in conjunction with other tests to check for functional or non-organic hearing loss. This is a type of hearing loss that can be difficult to diagnose since there are many potential sources for it along with several possible contributing factors.

During an otoacoustic emissions test, small probes are placed into the ear that’s being evaluated. One probe emits sounds into the ear. The other one is a microphone that measures any detected sounds that come back, or echo. There is no need for the patient to respond as the test is given. Results are displayed on a monitor an audiologist views during the test. Since the test is painless, babies often sleep as it’s being done.

A normally functioning cochlea produces four specific sounds. Spontaneous acoustic emissions occur naturally, but not in response to any sounds. Responses to short duration sounds are transient otoacoustic emissions. Soft echoes produced in response to two different sound sources of varying tones are distortion product otoacoustic emissions. Any responses to continuous tones are sustained-frequency otoacoustic emissions. Possible reasons for an absence of otoacoustic emissions include:

• Swimmer’s ear
• Abnormal middle ear pressure
• Cysts in certain parts of the ear or ear canal
• Ear drum damage
• Abnormal middle ear bone growth (otosclerosis)

Results from otoacoustic emissions tests alone cannot positively diagnose hearing loss or deafness. Even when patients fail an OAE test, results from speech, auditory brainstem response (ABR), pure-tone, and middle ear testing are typically taken into account to get a more precise understanding of hearing health. This is especially true when infants or newborns are OAE tested since being fussy during the test cam affect results, as can having fluid build-up or earwax in the ears.