Diagnostic Hearing Tests
Before commencing a hearing test, the audiologist will examine your ear canals with a video otoscope to determine the condition of the ear canal and eardrum. We can also provide you with clear and still images of the ear canal and tympanic membrane. If ear wax is present in sufficient quantity to interfere with the test then your Audiologist will remove this using specialized instruments.
Pure Tone Audiometry (PTA)
Pure tone audiometry is performed while you are in a sound booth. An Audiometer is used to present tones of varying pitch and loudness. The test signals are usually presented through calibrated headphones and a bone conductor. Occasionally insert earphones maybe used as well as presentation via a loudspeaker. You will be asked to respond each time you hear the tone by pressing a response button. The softest sounds you respond to are known as thresholds. These thresholds are recorded on an audiogram at each frequency tested. These results determine if a loss exists, the nature of any hearing loss detected, and the severity.
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Speech audiometry is used to determine your ability to discriminate the spoken word in quiet. Occasionally speech audiometry will be performed in the presence of background noise to determine how much difficulty challenging environments pose to the individual. The speech discrimination test is performed at several levels of loudness to determine the level which provides you with the best understanding. The results of speech discrimination testing can be predicted from the audiogram and deviations inform the Audiologist to consider other investigations.
Tympanometry and Acoustic Reflex Testing
Another important part of audiological assessment is tympanometry, which measures the mobility of the eardrum. A small probe is placed in the ear canal attached to a soft tip to create a pressure seal. The pressure in the ear canal is then changed to find the point at which the ear drum moves best. Abnormalities of pressure and movement can be detected with this test.
Acoustic Reflex Testing
Acoustic reflex testing is completed for each ear and may only be completed in conjunction with tympanometry. The acoustic reflex is a contraction of middle ear muscles that are connected to the ossicles, intended in nature to protect the ear from loud sound. If this test is required you will hear tones of varying loudness and pitch as the instrument determines the softest sound that will elicit a muscle contraction, or reflex. Acoustic reflex testing provides useful information about the type and severity of your hearing loss and its possible cause. It is also an important test in detecting problems in the auditory pathway beyond the level of the inner ear.
Otoacoustic Emissions (OAEs)
When sound is presented to the cochlea the outer hair cells twitch in response sending an “echo” back into the ear canal where it can be measured. Being a small signal averaging techniques are required to detect the response. A small probe in the ear canal is used to exclude extraneous noise and to conduct the stimulus to the ear and record the response. Otoacoustic emissions are very sensitive to hearing loss and are used extensively in newborn hearing screening programs as a quick, safe and efficient means of detecting loss. They have considerable value also in monitoring the effects of ototoxic medications due to their sensitivity to hair cell damage within the cochlea.
- OAEs are site-specific for cochlear (sensory) auditory dysfunction
- Ototoxic drugs exert their effect on outer hair cell function; OAEs are dependent on outer hair cell integrity
- OAE recording is electrophysiologic and is not dependent on patient behavioral responses: can be recorded form patients who, due to their medical condition, are unable to perform behavioral audiological tasks, or from infants and young children
- OAEs can detect cochlear dysfunction before it is evident by pure tone audiometry
- OAEs provide frequency-specific information
Auditory Evoked Potentials
Hearing involves not only the ear, but also the brain. When a sound is heard, we expect some change in the electrical activity from the cochlear and pathways upward to the auditory cortex in the brain. The Auditory Brainstem Response is a non-invasive, objective test, which can be used as an estimate of hearing loss or for assessment of neurological function. ABR can also assess the functional integrity of the central auditory pathway, and can contribute to the detect abnormalities, such as acoustic neuroma.