The Acoustic Otoscope
The AO was invented in 1986 by a pediatrician and sonar engineer, as a handheld device that analyzed sound waves bounced off the tympanic membrane to determine the presence of a middle ear effusion. The device emitted short pulses of sound with an intensity of 80 dB. A microphone determined the sum of emitted and reflected sound and displayed a graph of the reflectivity in arbitrary units. The amount of reflected sound energy rose with the likelihood that an effusion was present. Several years later, the AO was redesigned into a device that was based not on the intensity of the reflected sound but on the frequency spectrum of the reflected sound. It displays the output as a spectral gradient angle (SGA) which corresponds to the probability of effusion. Unlike tympanometry the AO does not require a seal, can be used in a crying child and measurements can be obtained if the canal is partially occluded by cerumen. In contrast to tympanometry, AO measurements can be obtained in seconds.
The current version of the AO is manufactured to the exact specifications of the original Ear Check Pro, and I now use it regularly when evaluating children with upper respiratory infections who may or may not be complaining of ear pain. As we know many children are less than cooperative for ear examinations. As with the original EarCheck Pro, in my experience, a large SGA, almost always excludes an AOM or OME as a diagnostic possibility. This is not to say that that one should not perform otoscopy, when the AO output indicates a large SGA! Rarely I see a child with erythema of the TM, not due to crying, without fluid behind the TM, that I would consider a very early OM.
In a normal ear, a significant portion of the sound energy produced by the AO is transmitted into the middle ear, and little is reflected, producing a wide spectral gradient angle.However, in the presence of a middle ear effusion, most of the sound energy is reflected, producing a narrow spectral gradient angle.
The AO, manufactured by Check My Ear LLC (Lincoln, Nebraska) costs $895 and is powered by two AA batteries. A calibration tube is provided and should be used at least once per month to make sure the device remains within specifications. It is used in conjunction with a disposable ear tip, and a package of 100 ear tips sells for $70. As shown in the video one places the tip of the AO in the ear canal pointing toward slightly forward and depresses and holds the right or left button depending on the ear being tested. I tell the child he will hear some funny noises during the test. It usually takes about 10 seconds, sometimes less to obtain a reading. One records the measurement from both ears and then performs otoscopy. Check My Ear LLC eventually may develop a stand for the AO with printing capability. AO measurements are reimbursed at about $20 per testing using the CPT code 92567.
The device is so easy to use so that nurses can perform AO measurements while rooming the patient. As the device is relatively inexpensive (compared to a $4000 or more tympanometry device), the AO pays for itself in a matter of weeks.