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Alternative names
Audiology; Audiometry; Audiography (audiogram)
Definition
A hearing test tests your ability to hear sounds. Sounds vary according to the intensity (volume or loudness) and the tone (the speed of sound wave vibrations).
Hearing occurs when sound waves move to the nerves of the inner ear and then the brain. Sound waves can travel to the inner ear by air conduction (through the ear canal, eardrum, and bones of the middle ear) or bone conduction (through the bones around and behind the ear).
INTENSITY of sound is measured in decibels (dB):
- A whisper is about 20 dB
- Loud music (some concerts) is around 80 to 120 dB
- A jet engine is about 140 to 180 dB
Usually, sounds greater than 85 dB can cause hearing loss in a few hours. Louder sounds can cause immediate pain, and hearing loss can develop in a very short time.
TONE of sound is measured in cycles per second (cps) or Hertz:
- Low bass tones range around 50 to 60 Hz
- Shrill, high-pitched tones range around 10,000 Hz or higher
The normal range of human hearing is about 20 Hz to 20,000 Hz, and some animals can hear up to about 50,000 Hz.
How the test is performed
Air conduction is tested by having you wear earphones attached to the audiometer. Pure tones of controlled intensity are delivered, to one ear at a time. You are asked to raise a hand, press a button, or otherwise indicate when you hear a sound. The minimum intensity (volume) required to hear each tone is graphed. An attachment called a bone oscillator is placed against the bone behind each ear (mastoid bone) to test bone conduction.
How to prepare for the test
No special preparation is needed.
How the test will feel
There is no discomfort. The length of time varies. An initial screening may take about 5 to 10 minutes. Detailed audiometry may take about 1 hour.
Why the test is performed
This may be a screening test to detect a hearing loss at an early stage. It may also be used when there is difficulty in hearing from any cause.
Common causes of hearing loss include:
- Chronic ear infections
- Ruptured eardrum
- Acoustic trauma
- Occupational hearing loss
- Head injury
- Inherited conditions
- Diseases of the inner ear
- Medications that can be toxic to the nerve of the inner ear, including certain antibiotics (such as neomycin), diuretics, and large doses of salicylates (such as aspirin)
Normal Values
- The ability to hear a whisper, normal speech, and a ticking watch is normal.
- The ability to hear a tuning fork through air and bone is normal.
- In detailed audiometry, hearing is normal if tones from 250 Hz through 8000 Hz can be heard at 25 dB or lower.
What abnormal results mean
There are many different kinds and degrees of hearing loss. Some include only the loss of the ability to hear high or low tones, or the loss of only air or bone conduction. The inability to hear pure tones below 25 dB indicates some extent of hearing loss.
The extent and kind of hearing loss may give clues to the cause and the prognosis (probable outcome).
The following conditions may affect test results:
- Acoustic neuroma
- Acoustic trauma
- Age-related hearing loss
- Alport syndrome
- Labyrinthitis
- Meniere's disease
- Occupational hearing loss
- Otosclerosis
- Ruptured or perforated eardrum
What the risks are
There is no risk |
