Classification of Hearing Loss
- Mild Hearing Loss – 26-40 dB hearing threshold
- Moderate Hearing Loss – 41-55 dB hearing threshold
- Moderate to Severe Hearing Loss – 56-70 dB hearing threshold
- Severe Hearing Loss – 71-90 dB hearing threshold
- Profound Hearing Loss – 91dB or greater hearing threshold
Tests of the Auditory Pathway
These do not determine cortical processing of sound.
- Otoacoustic Emissions (OAEs) – Useful for children of all ages.
OAEs measure the response of the cochlear outer hair cells of the inner ear to a sound. (Information on hearing and ear anatomy). The cochlea changes sound vibrations into nerve impulses which travel to the brain allowing sound perception. A small probe with a sensitive microphone is placed in the ear canal, delivers the sound and detects the response. When the cochlea reacts to a sound, it emits acoustic energy called an Otoacoustic Emission as a result of outer hair cell movement. This emission can be picked up by a probe placed in the ear canal. OAEs will not be detected in ears with more than a mild hearing loss. OAEs will not detect an auditory neuropathy.
- Brainstem Auditory Evoked Responses (BAER, or Auditory Brainstem Response [ABR]) – Useful for children of any age.
An objective measure of hearing responses to a click or tone stimulus in each ear which measures electrophysiologic activity of the auditory nerve and brainstem pathways of hearing. The child must like quietly with eyes shut to prevent muscular interference with the test. This often requires sedation of the young child or infant. Four electrodes are placed on the child’s head (earlobes and forehead) to detect the response. The sound stimulus (a click or a frequency-specific sound burst) is presented and the resulting brainwave is analyzed. An automated screener provides a pass-fail report without need for test interpretation by an audiologist.
Tests of Hearing
- Behavioral Testing
- Behavioral observation audiometry (BOA)- Useful in children at a developmental age less than 5-6 months
Child is placed on a parent’s lap in a sound booth. Sound stimuli are presented through speakers to the child’s right and left. Examiner observes the infant for behavioral changes such as startling, cessation of movement, eye widening and rudimentary head turning in response to a sound. As a normally developing infant nears 4 to 6 months of age, responses to softer sounds and head turn toward the sound source may be seen. This test can exclude severe and profound hearing loss but is inadequate to confirm lesser hearing loss or confirm normal hearing.
- Visual Reinforcement Audiometry (VRA)- Useful in children at a developmental age of 5-6 months to 2 1/2 years old
Speech and frequency-specific sounds are presented through speakers in a sound booth. When the child looks toward the source of the sound, an animated toy or other visually-pleasing stimulus is activated as a reinforcer for the child. The sound is then presented while the visual reinforcer is withheld. If the child looks for the source of the sound, the visual reinforcer is presented as a reward. This testing method measures the hearing of the better ear, hence cannot rule out a unilateral hearing loss. Auditory perception/cortical processing of sound is measured by this method of hearing assessment.
- Play Audiometry – Useful in children at a developmental age of 2 1/2 to 5 years
Speech and frequency-specific sounds are presented through earphones and/or bone oscillator. The child is conditioned to perform a task, such as placing a peg in a pegboard, each time a sound stimulus is heard. Ear-specific results are obtained. Measurements include hearing thresholds, speech recognition threshold and speech discrimination ability.
- Conventional Audiomety – Useful in children at a developmental age of 4 years and older
Speech and frequency-specific sounds are presented through earphones or a bone-oscillator. The child is instructed to raise a hand or press a button each time a sound stimulus is heard. Ear-specific results are obtained. Speech threshold and speech discrimination can also be tested.
This is not a test of hearing but evaluation of the middle ear (behind the eardrum) for fluid accumulation. Measures the volume of the external ear canal, compliance of the middle ear system and the presence of effusion or eardrum retraction. For more information – Tympanometry. Onusko E. American Family Physician. 70:1713-1720, November 2004
- Pediatric audiology: A review. Gregg RB, Wiorek RL, Arvedson JC. Pediatrics in Review. 25:224-234, 2004.
- Evaluation of hearing loss in infants and young children. Jacobson J, Jacobson C. Pediatric Annals. 33(12):811-821, Dec 2004.