Testing Infants
Otoacoustic emissions (OAE) assessment is a relatively new procedure to help determine the status of your child's hearing. The OAE evaluation is painless, and usually takes just a few minutes for each ear to conduct. The procedure assesses the functioning of the microscopic hair cells in the inner ear (Cochlea) that are responsible for adequate hearing. It has been estimated that in approximately 3 per 1000 live births, a permanent hearing loss in both ears is present. Hearing loss is the most frequently occurring birth defect. All children should be screened to determine if such a loss is present. The earlier a hearing impairment is detected, the greater the chances of the child developing normal speech and language.
The OAE assessment is just one part of a battery of tests that will be used. Before any testing begins, Dr. Lowe will look in your child's ears with a small video camera to make sure the ears are not blocked with earwax or other debris. If the ear canals look open, then the next step may be to obtain a tympanogram. That is a procedure to determine if your child has any fluid in the middle ear behind the eardrum. Significant middle ear fluid can affect the OAE assessment. If your child has tubes in his/her eardrums, the OAE testing will still be conducted since results can be obtained with tubes in place.
Following the tympanogram, testing may be conducted in a sound treated room. Your child will be seated on your lap and special tones will be presented from loudspeakers. Dr. Lowe will try to condition your child to respond to the sounds. Animated animals are used as reinforcement, and usually, children respond well to the testing. This type of testing is often call visual reinforcement audiometry (VRA). This test will not be conducted if your child is under the age of approximately seven months since those children are often not mature enough to make the connection between the tones and the reinforcement. After testing in the sound treated room, Dr. Lowe will often give the parent and the child a break before proceeding with the OAE testing.
The otoacoustic emissions that Dr. Lowe will try to measure using a computer, are generated by the outer hair cells in the inner ear. We know that normal functioning hair cells are necessary for proper hearing, and they are also necessary for obtaining normal otoacoustic emissions. The emissions are actually noises produced by the microscopic hair cells as they move in response to sound. Dr. Lowe uses equipment that produces pure tones into the ear. During the test, a small soft plug will be inserted into your child's ear.
The right ear is usually tested first. The computer will then do a check to make sure the plug is fitting properly, and to make sure the appropriate tones are being produced. Then the computer will start presenting tones into your child’s ear. The tones are not loud or unpleasant. The tones presented by the earplug travel through the middle ear and then into the inner ear. The hair cells are stimulated and start moving, which produces noise. The noises produced by the moving hair cells then travel back out through the middle ear and then into the ear canal where they are picked up by a microphone in the ear plug. This is why it is important to determine if there is any fluid in the middle ear by conducting the tympanogram test. Significant middle ear fluid will not allow the sounds to travel well in either direction through the middle ear. It is also important that noise in the room, and the noise from your child be kept to a minimum because the sounds that the microphone is detecting in the ear canal are extremely soft. The sounds from the microphone are then sent to the computer for special analysis.
Normal results on the OAE assessment indicate that the outer hair cells in the inner ear are functioning properly and that your child’s hearing should be normal or near normal. Normal OAEs also suggest normal middle ear function (no significant fluid). There is always the possibility of problems in the pathways to the brain, but the likelihood of that happening is very small. Most experts agree that problems beyond the hair cells in the inner ear represent less than 1% of all children with hearing loss, or less than 3 children per 100,000 in the general population. If visual reinforcement testing was conducted in the sound treated room as discussed above, and if those results were normal, then we would know that your child perceives the sound and the entire auditory system should be functioning normally.
If a child fails the OAE assessment, and the tympanograms were also abnormal, then a repeat tympanogram and OAE test should be considered following medical management. If the child fails the OAE assessment, and the tympanograms were normal, then a repeat OAE should be considered. Also, the child’s pediatrician may want to consider a referral to an otologist (physician who specializes in diseases of the ear) for a thorough examination and possible further testing.
Finally, there are some instances where other testing should be conducted. This includes infants or children with the following: meningitis, cytomegalovirus, asphyxia, hyperbilirubinemia, and head trauma. These children should receive testing that is sensitive to problems beyond the hair cells in the inner ear.
ps: Keep your young rockers away from intense noise! Did you know that some toys can be harmful to your child's hearing? If it sounds too loud to you, then keep that noise away from your child. Remember, the noise may not cause pain to your ears, but it can still be damaging.