Diagnostic Audiometric Tests
Comprehensive audiometry includes a number of tests which help the audiologist assess
the type and degree of a patient's hearing impairment These tests can be
performed for almost any patient. These tests include:
- Pure tone audiometry
Tests using pure tone signals determine a patient's hearing
sensitivity for the range of typical everyday sounds, particularly
speech sounds. During pure tone testing, the patient is seated in a
sound treated room. He or she listens for discreet tones under
earphones. If warranted, the tests are repeated with a bone conduction
headphone, which is used to confirm or rule out a middle ear component
of hearing impairment.
- Speech audiometry
Speech testing includes detection and discrimination tasks. Speech
discrimination is useful in determining whether the patient processes
speech sounds normally. Good speech discrimination scores typically
indicate a patient can benefit from amplification, if warranted.
- Immittance audiometry
Immittance testing is used to determine resistance in the middle
ear system. These tests include tympanometry and acoustic reflexes.
Tympanometry measures the flexibility of the eardrum (tympanic
membrane), and acoustic reflexes help assess both nerve conduction and
the middle ear system. Immittance tests help confirm the presence of
middle ear fluid, a functioning ventilation tube, or a perforation.
Advanced audiological tests include
Auditory Evoked Brainstem Response (ABR), Evoked Otoacoustic Emissions
(OAEs) and Electrocochleography (ECoG). These are termed "site of lesion" tests because they are
used to determine whether a specific hearing loss is sensory (cochlear) or
neurological in nature.
- Auditory evoked brainstem
response (ABR)
ABR testing is primarily used to assess the auditory nerve function.
Brainwaves generated in the auditory pathway are recorded and analyzed
while the patient listens to rapid clicking sounds. Electrodes pick up
the electrical signal traveling on the auditory nerve from the inner
ear to the brainstem. ABR recordings are helpful in ruling out
acoustic neuromas. The ABR can also be used to determine an
approximate hearing threshold for the higher frequencies, and is
useful for assessing hearing loss in infants and children when
conventional audiometry is not possible.
- Evoked otoacoustic emissions (OAEs)
OAE tests assess the function of the cochlea by relying on a natural
phenomena, emissions, which occur in normally functioning ears. When a
normal cochlea is stimulated with sound, a (very weak) signal, the
emission, is returned from the inner ear through the tympanic
membrane. This emission can be recorded by special microphones placed
in the ear canal.
- Electrocochleography (ECoG)
ECoG testing is usually performed in conjunction with ABR and ENG
for assessment of Meniere's disease in the presence of hearing loss
and vertigo. Electrodes are placed near the tympanic membrane.
Responses are collected and analyzed much like the ABR, looking for an
abnormal electrical pattern within the cochlea, rather than the
auditory nerve.
- Electronystagmography (ENG)
ENG testing involves a series of tests to assess balance function. The
tests are designed to isolate abnormal dizziness, if possible, to
either the inner ear(s) or central nervous system.
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