OTOACOUSTIC EMISSIONS
Otoacoustic Emissions are small sounds caused by motion of the eardrum in response to vibrations from deep within the cochlea. The healthy cochlea (inner ear) creates internal vibrations whenever it processes sound. Impaired cochleae usually do not. Some healthy ears even produce sound spontaneously as internal sounds are processed and amplified. As described later, the cochlea’s capacity to generate sound is intimately associated with its achievement of normal auditory threshold, and the underlying mechanism is very easily damaged. To record the sounds made by the cochlea an earphone and microphone combination probe is fitted into the ear canal. The middle ear has to be working efficiently in order to conduct the minute cochlear vibrations back to the ear drum- acting like a stethoscope. A good fitting of the probe is important. Closure of the ear canal by the probe greatly increases the sound pressure created by any eardrum vibration. It also excludes unwanted external sounds. Normally the ear to be tested is given mild acoustic stimulation to evoke an otoacoustic emission. Clicks, tones, noise and even speech all elicit and OAE response. There is a unique OAE response to every stimulus. Depending on the nature of the sound presented, different signal processing techniques are effective in extracting the OAE from the stimulus and other noises. The common technologies are "TEOAE" when clicks or tone bursts are used, "DPOAE" when dual tone stimuli are used, and SFOAE, when single tone stimulation is used. It is important to remember "TEOAE and "DPOAE" and "SFOAE" instruments deliver different views of the same auditory process and a combination of measurements is needed to get a complete picture. The essential fact about OAE’s is that their presence is always good news about cochlea and middle ear function. It usually means hearing is within normal limits around the stimulus frequency evoking the response – but this is not guaranteed. There can be problems further along the auditory pathway and there is much still to learn about OAE’s and cochlear physiology.
YOUR BABY’S HEARING
Why is it important for me to know about my baby’s hearing now?
Hearing impairment in infants is easy to ignore because it is invisible and infants and
toddlers cannot tell us they are unable to hear. Yet, hearing impairment is the most
common birth defect -- 6 out of 1,000 babies are born with it -- and one of the most
treatable. Because babies learn to speak by listening, the child who is unable to hear
normally, will not develop speech and language normally. The most critical years for the
development of language are from birth to three years of age. Early identification of
hearing impairments enables us to give the child the special attention needed to aid in
language development as well as in social, emotional, and academic development.
How can my baby’s hearing be screened?
We use a procedure called transient evoked otoacoustic emissions (TEOAE). This procedure
(CPT 92587) actually measures the vibration of the inner ear when a sound is heard. The
test causes no discomfort and is usually administered while the child is sleeping. The
test takes less than ten minutes to complete.
What does PASS/REFER mean?
The instrument will screen each ear independently. The output is determined as PASS
(indicating the screened ear is normal) or REFER (indicating additional screening is
needed).
What happens if my baby refers?
If the baby REFERS on either ear, the screen is run again at no charge. If a refer is
present on the second screen, a diagnostic ABR screen is performed to determine the
location and extent of the hearing loss. The diagnostic ABR screen uses a different piece
of equipment and is much more complex. If a hearing loss is confirmed, your baby will be
scheduled as an outpatient for further screening.
How long does this screen take?
The screening takes approximately fifteen minutes provided that your baby is quiet. The
screening time depends entirely upon how quietly your baby is resting. The diagnostic ABR,
if needed, takes approximately one hour.
Is this screen painful to my baby?
No. The screen is completely non-invasive and most infants sleep through the screening.
Where is the screening performed?
We do the OAE prior to hospital discharge. We can also perform the procedure without any
sedation in our Falls Church office.
Who does the screen?
An individual who has been trained to operate the screening equipment will perform the
screening. The results will be reviewed and you will be notified of the outcome prior to
discharge.
What can you do if a hearing impairment is present?
Intervention is dependent upon the type of hearing impairment present. Medical
consultation and or surgical follow-up may be appropriate. If your child requires hearing
aids, it is ideal that they are fit before six months of age and that audiometric
follow-up and rehabilitation are initiated accordingly.
What if I choose not to have the screen at this time, can I schedule it for later?
Yes. You can schedule your baby as an outpatient. The screen must be done before six
months of age. But remember, the idea of the program is early identification, which
produces the greatest advantage. An undetected and untreated hearing impairment can
present a great disadvantage for the child, and can permanently damage speech and
language. The sooner the impairment is identified the greater the opportunity the child
has to develop normal speech and language. Hearing impaired children can and do lead
normal and happy lives. Don’t let an undetected impairment go untreated.
NEWBORN SCREENING WITH OAE’s
What could be simpler than testing an infant’s hearing with an insert-earphone? It takes only a few seconds to record the transient otoacoustic emissions in a quiet office from a typical newborn who has clean ear canals and a well-drained middle ear. If conditions are not ideal it can take longer – but 5 minutes is an exceptionally long time for an experienced OAE screener to test a newborn – and it would usually mean that the newborn was not ready to be tested. Transient OAE technology is generally preferred for screening at this time because the instrumentation provides very fast feedback to the screener on general probe fit, noise and test outcome. DPOAE’s can also be used effectively. TEOAE screening has the advantage of testing a wide range of frequencies individually yet simultaneously giving a continuous panorama of cochlear function with frequency. Around 100 universal screening programs in the USA currently use TEOAE’s. A 1996 survey by the National Center for Hearing Assessment and Management (NCHAM) showed referral rate of less than 5%. The reportedly very high sensitivity of the technique for universal screening has not been challenged, despite many hundreds of thousands of TEOAE screenings starting with the Rhode Island Hearing Assessment Project in 1989. OAE screening has proven very effective in the detection of hearing impairment in newborns, even though the neural pathway is not being assessed. Failure to show an OAE is probably the single most important risk factor for hearing impairment but other risk factors should never be ignored. Any risk of neurological significance means an ABR test must also be conducted. To date, among the hundreds of thousands of OAE screenings monitored by NCHAM the incidence of late onset hearing losses missed by OAE screening appears to be very low – around 1% of the hearing impaired population. OAE’s appear to be ideal for the first stage of universal screening programs. (NIH Consensus Statement 1993).
Links
National Center for Hearing Assessment & Management
American Academy of Audiology, Inc.
