Audiometry - Otogram

• Hearing tests are usually done to:
  • To screen children and teens for hearing loss.
  • To evaluate possible hearing loss in anyone who has noticed a persistent hearing problem in one or both years or has had difficulty understanding words in a conversation.
  • To screen for hearing problems in older adults. Hearing loss in older adults is often mistaken for diminished mental capacity. (for instance, if the person does not seem to listen or respond to conversation).
  • To screen for hearing loss in people who are repeatedly exposed to loud noises or who are taking certain antibiotics, such as gentamicin or streptomycin.
  • To determine the type and amount of hearing loss (conductive, sensorineural, or mixed).

• Tell your doctor if you:
  • Have recently been exposed to any painfully loud noise or to a noise that made your ears ring.
  • Avoid loud noises for 16 hours prior to having a thorough hearing test.
  • Are taking or have taken antibiotics that can damage hearing, such as gentamicin or streptomycin.
  • Have had any problems hearing normal conversations or noticed any other signs of possible hearing loss.
  • Have recently had a cold or ear infection.

What happens during the test?

The test consists of seven separate sections:

1. Air Conduction - The air conduction test presents a series of single-frequency tones (ranging from 20 Hz to 8000 Hz) to the patient through the ear inserts. This test measures (in decibels) the lowest level that the patient can hear a tone of a single frequency. Masking is used to determine which ear is hearing the tone.
   
   
2. Bone Conduction - The bone conduction test uses a bone vibrator placed on the patient's forehead to vibrate the skull which then stimulates the hair cells of the cochlea. The hair cells are attached to the 8th cranial nerve which transmits the signal to the brain as sound. It is important to perform bone conduction to determine if the cause of a patient's hearing loss is the result of damage to the cochlea versus some other problem with the ear canal, eardrum, or ossicular chain (hearing bones). Masking is used to determine which ear is hearing the tone.
   
   
3. Speech Reception Threshold - While pure tone testing measures hearing thresholds of discrete frequencies, speech is made up of a combination of many frequencies and is tested separately. The speech reception threshold test measures (in decibels) the lowest level at which a patient can understand speech.
   
   
4. Speech Discrimination - Speech discrimination test presents one word (i.e. mop) to the patient at a consistent, comfortable sound level calculated using the articulation index. Images of both the word presented as well as rhyming words (i.e. stop, top, shop) are presented on the screen. The patient must discriminate between the words and choose the image that matches the word presented. This test determines weather or not the patient has difficulty discriminating between words that sound similar.
   
   
5. Tympanometry - Measures the change in physical properties of the middle ear system and ear drum as air pressure in the external ear canal is varied. Tympanometry is conducted by placing a probe into the patient's ear and creating an air-tight seal between the walls of the ear canal and the probe. They tympanometer then pulls and pushes air through the probe into the ear canal while a tone is emitted into the ear. A microphone system in the probe then measures the sound presentation level and tests the air pressure and volume inside the ear. Problems with air pressure can occur if fluid is behind the ear drum or if the ear drum is damaged.
   
   
6. Acoustic Reflex - The acoustic reflex threshold test is conducted by placing a probe in each ear and presenting 1000 Hz and 2000 Hz frequency tones at a high sound level. These tones should cause a reflex of the stapedius muscle which is attached to the stapes bone muscle like a knee reflex test. When the reflex occurs, a signal is sent back to the probe indication that the reflex is healthy. This test is used to determine the integrity of the 8th cranial nerve as well as the ossicular chain.
   
   
7. Otoacoustic Emissions (OAE) - Otoacoustic emissions tests a patient's cochlea by presenting a stimulus into the ear and recording weather the response of the ear drum to the stimulus is normal or abnormal. OAE's are performed to test the health of the outer hair cells in the cochlea.

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