Otoacoustic emissions fall into two categories; Spontaneous and Evoked.
Spontaneous otoacoustic emissions (SOAEs) occur naturally in the ear without external stimulation while evoked OAEs are measured after the presentation of a stimulus to the ear. OAEs are evoked using a transient stimulus such as a click or tone burst (TEOAE), using a pure-tone stimulus (SFOAE) or using a pair of pure-tone stimuli (DPOAE).
The application of OAEs in screening is very different to that when used for diagnostic purposes.
In screening, the objective is to separate persons with an auditory disorder that will interfere with communication, from those who do not have a communicatively important auditory disorder.
In diagnostic, a test battery approach is commonly used to get the big picture about a patient’s hearing condition.
Testing should always be conducted in a quiet room away from excessive noise (equipment, other patients, etc). Testing in a noisy environment can prolong test times and lead to uninterpretable or a misinterpretation of test results.
As the status of the outer and middle ear can affect OAE recordings, it is recommended to conduct otoscopy tests and impedance measurements prior to OAE testing.
Otoacoustic emissions devices typically include a range of default test protocols for screening and/or diagnostics.
Unfortunately, there is not one test protocol that fits all, and sometimes a standard protocol may need adjustment for an individual patient. It is therefore important that the clinician understands the rationale for certain parameter settings and how changing certain parameters might affect the test results.
There are numerous reasons for choosing one OAE test methodology over the other.
Some prefer the TEOAE methodology when trying to conduct a quick OAE screening on a child while others find DPOAEs more suitable when assessing adult patients.
Either way, both methodologies assess outer hair cell function and provide important information about the status of the cochlea.
Repeating the OAE test is good practice and provides assurance to the clinician that the response shown on the screen is true and valid. While repeat testing takes extra time, it provides certainty when analyzing OAE measurements.
Ph.D., Interacoustics OAE Specialist