Otoacoustic emissions (OAE) are acoustic signals that are given off by the inner ear when it is receiving sounds. They are echoes of tiny vibrations given off by the stereocilia, tiny hair cells in the cochlea that turn sound impulses into electrical signals to be sent to the brain through the auditory nerve.
In a person with normal hearing, these otoacoustic emissions can be detected by specialized probes inserted into the middle ear. But if the inner ear has been damaged, or the sound pathway from the outer ear has been blocked, the emissions are not present.
This fact has lead to the development of a simple, non-invasive test that speech-language pathologists (SLPs) and audiologists can use to investigate potential hearing loss, and to isolate potential causes of hearing loss, even in patients who are otherwise unable to self-diagnose and self-report hearing problems. This has completely changed the approaches to finding and treating deafness in children by allowing newborns to be screened for hearing loss.
Otoacoustic Emissions Screening Helps Identify and Solve Hearing Problems Early
Because the procedure is relatively simple, SLPs in almost every practice setting can use it, though they may refer more difficult-to-test patients to an audiologist to get more in-depth results.
The primary setting where SLPs perform otoacoustic screening is in school systems. The robust U.S. Early Hearing Detection and Intervention (EHDI) program (active in all 50 states) involves periodically screening children from early childhood through school age. The program has ensured that more than 95 percent of all newborns are screened for hearing loss shortly after birth. The program has been enormously effective in providing a track to getting infants and children the services they need. In fact, a full 77 percent of children who tested positive for hearing loss have ended up in an intervention program within six months of the issue being detected.
According to a set of studies conducted in the early 2000s by the National Institutes of Health (NIH), this early detection and intervention process boosts language skills and social development in deaf children to levels comparable to those of their non-deaf peers, regardless of the degree of hearing loss.
Basic Hearing Tests Usually Precede OAE Screening
The exam generally begins with a simple otoscope inspection of the external ear canal for any abnormalities that may effect hearing. Blockage or other conditions found in the outer ear can also contraindicate OAE screening, as the equipment in otoacoustic tests has to be able to reach the middle ear.
With patients who are old enough and able to respond to stimuli, pure tone testing can be used. A steady or warbled tone at a certain volume is played and the subject indicates when they have heard it by raising the right or left hand, whichever one corresponds to the ear in which they hear the sound.
OAE Screening Provides Fast and Effective Results Even When a Patient Can’t Communicate
OAE testing is performed on very young patients who can’t be relied on to respond predictably and accurately to the tone, or in cases when the mechanical limitations of the inner ear are only detected as a result of certain symptoms (if, for instance, hearing is believed to be impaired, but the cause has not yet been isolated).
OAE screening is actually faster than pure-tone testing, but requires a quiet environment for the equipment to operate correctly. Because the patient doesn’t need to do anything other than sit quietly, it’s a good test for patients who are very young or who have other disabilities that limit interaction.
The screening itself is conducted with a small, handheld device with a flexible probe on the end. The probe is inserted into the ear, the device is activated, and within 30 seconds a simple pass/fail result is automatically generated.
An OAE itself is not a complete test of hearing. If hearing loss is suspected but not confirmed with an OAE or pure tone test, tympanometry (an air pressure test that can find issues with the ear drum or eustachian tubes) may also be performed. SLPs are responsible for deciding when to refer patients to an audiologist for more in-depth testing if hearing loss is discovered.
SLPs may not only be responsible for performing the screening itself but also for managing the screening program and communicating with parents when children are being tested. This also requires familiarity with state regulations related to Early Hearing Detection and Intervention programs, which may or may not require parental permission.
Although hearing loss is only one condition of a large number of disorders that SLPs participate in treating, it is one of the easiest to detect and most beneficial to catch early. Once it has been diagnosed, SLPs often continue to be involved with that patient, providing therapies designed to assist speech and language learning in the face of deficits that come with hearing loss.