Do You Understand Audiometric Evaluations?

Here’s the lowdown on all the abbreviations and words you often hear:

ABR or auditory brainstem response

The auditory brainstem response (ABR) test gives information about the inner ear (cochlea) and brain pathways for hearing. This test is also sometimes referred to as auditory evoked potential (AEP). The test can be used with children or others who have a difficult time with conventional behavioral methods of hearing screening. The ABR is also indicated for a person with signs, symptoms, or complaints suggesting a type of hearing loss in the brain or a brain pathway.

The ABR is performed by pasting electrodes on the head—similar to electrodes placed around the heart when an electrocardiogram is run—and recording brain wave activity in response to sound. The person being tested rests quietly or sleeps while the test is performed. No response is necessary. ABR can also be used as a screening test in newborn hearing screening programs. When used as a screening test, only one intensity or loudness level is checked, and the baby either passes or fails the screen.

ASSR

Auditory Steady State Response (ASSR) is a test used to determine hearing loss in children who are either too young to respond or are unable to respond. Most children are referred for an ASSR after a newborn hearing screen in the hospital indicates the possibility of hearing loss. This test is typically performed at the same time as the ABR (Auditory Brainstem Response).

The audiologist will scrub the skin where four electrodes will be placed (forehead and behind the ears). Once your child is sleeping, the audiologist will place small ear phones into his or her ears that will play tones of varying frequency (pitch) and intensity (loudness). This sound travels from your child’s ears to the brain (through the auditory pathway) where it is recorded through the electrodes. ASSR provides an accurate, frequency-specific estimate of the behavioral pure-tone audiogram.

OAE

Otoacoustic emissions (OAEs) are sounds given off by the inner ear when the cochlea is stimulated by a sound. When sound stimulates the cochlea, the outer hair cells vibrate. The vibration produces a nearly inaudible sound that echoes back into the middle ear. The sound can be measured with a small probe inserted into the ear canal.

People with normal hearing produce emissions. Those with hearing loss greater than 25–30 decibels (dB) do not produce these very soft sounds. The OAE test is often part of a newborn hearing screening program. This test can detect blockage in the outer ear canal, as well as the presence of middle ear fluid and damage to the outer hair cells in the cochlea.

Otoscopic exam

Otoscopy is an examination that involves looking into the ear with an instrument called an otoscope (or auriscope). This is performed in order to examine the ‘external auditory canal’ – the tunnel that leads from the outer ear (pinna) to the eardrum.

Inspection of the eardrum can also provide a lot of information about what’s happening within the middle ear – the space within the skull where the hearing and balance mechanisms are situated.

The examination is performed by gently pulling the outer part of the ear upwards and backwards. This action straightens the external auditory canal, which has a natural curve, and makes it easier to see the eardrum.

The normal external auditory canal has some hair, often lined with yellow to brown wax. The total length of the ear canal in adults is approximately 2cm, which gives it a resonance frequency of approximately 3400 Hz, which is an important frequency region for understanding speech.

Abnormal findings may include:

  • a dry, flaky lining suggestive of eczema. The usual symptom is of itch.
  • an inflamed and swollen, narrowed canal, possibly with a discharge indicating infection (otitis externa). The usual symptoms include itch, local discomfort, a discharge and often an unpleasant smell from the ear.
  • wax obscuring the eardrum.
  • a foreign body in the ear, such as the rubber from the end of a pencil.

Tympanometry

Tympanometry is an examination used to test the condition of the middle ear and mobility of the eardrum (tympanic membrane) and the conduction bones by creating variations of air pressure in the ear canal.

Tympanometry is an objective test of middle-ear function. It is not a hearing test, but rather a measure of energy transmission through the middle ear. The test should not be used to assess the sensitivity of hearing and the results of this test should always be viewed in conjunction with pure tone audiometry.

Tympanometry is a valuable component of the audiometric evaluation. In evaluating hearing loss, tympanometry permits a distinction between sensorineural and conductive hearing loss, when evaluation is not apparent via Weber and Rinne testing. Furthermore, in a primary care setting, tympanometry can be helpful in making the diagnosis of otitis media by demonstrating the presence of a middle ear effusion.

Acoustic reflexes

Acoustic reflex measures add information about the possible location of the hearing problem. Everyone has an acoustic reflex to sounds. A tiny muscle in the middle ear contracts when a loud sound occurs. The loudness level at which the acoustic reflex occurs—or the absence of the acoustic reflex—gives information to the audiologist about the type of hearing loss.

BOA or Behavioral Observation Audiometry

BOA tests hearing by provoking a behavioral response to an acoustic stimulus. Used for infants from birth through seven months, the patient is observed for responses such as body movement, eye widening, eye opening or change in sucking rate after a stimulus is provided. This test is used to rule out hearing loss and related conditions

 VRA or Visual Reinforcement Audiometry

During VRA, the child uses earphones or sits between two speakers from which certain sounds are presented. A tone, speech or music may be played in order to encourage the child to respond by shifting their eyes or turning their head. When the child responds to the stimulus, they are rewarded with an interesting visual display, such as an animated toy. VRA performed with headphones can test each ear separately, while testing without headphones evaluates the child’s sound field instead. This test is ideal for children between the ages of seven and thirty months.

Play Audiometry

Conditioned play audiometry can be used as the child matures and is commonly used with toddlers and preschoolers (ages 2–5). The child is trained to perform an activity each time a sound is heard. The activity may involve putting a block in a box, placing pegs in a hole, or putting a ring on a cone.

Bone conduction testing

If there is a blockage, such as wax or fluid, in the outer or middle ears, a method called pure- tone bone conduction testing may be used. With this technique, the blockage is bypassed by sending a tone through a small vibrator placed behind the ear (or on the forehead). The signal reaches the inner ear (or cochlea) directly through gentle vibrations of the skull. This testing can measure response of the inner ear to sound independently of the outer and middle ears. In these cases, this test helps the audiologist determine the type of hearing loss being measured.