Hearing Loss
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Hearing Loss
Many different conditions can result in hearing impairment and the cause can be located in any part of the hearing system. At any age, hearing can be damaged gradually or suddenly. Most often hearing is gradual and painless.
Structures of the ear
Conditions affecting the outer and middle ear cause a ‘conductive’ type of hearing loss. Conditions affecting the inner ear and the auditory nerve cause a ‘sensorineural’ hearing loss or ‘nerve deafness’.
Both types can occur in the same person. Your outer ear gathers sound waves and funnels them down into the ear canal, striking the eardrum, causing it to vibrate. Three tiny bones in the middle ear conduct the vibrations from the eardrum to the cochlea in the inner ear. If anything interferes with the transfer of sound waves up to this point the type of hearing loss that may result is called conductive. The sound vibrations having reached the inner ear create waves in the fluid inside the inner ear, stimulating thousands of delicate hair cells. This generates nerve impulses in the auditory nerve, which lies just beyond the cochlea, which are carried to the brain therefore, making sense of sound. Anything that damages the hair cells or blocks the transmission of the nerve impulses can lead to sensorineural hearing loss.
Conductive hearing loss may be temporary or permanent, can be caused caused by a buildup of earwax or an ear infection, or other middle ear conditions. Sensorineural hearing loss, which is almost always permanent and far more common and be caused by aging, excessive and prolonged noise exposure, infections, hereditary factors as well as a host of other causes. Surgical procedures and medications can treat conductive hearing loss, but rarely sensorineural hearing loss.
Pure Tone Audiogram:
The hearing test is plotted on an audiogram which shows the degree of hearing loss (dB or decibel on the vertical axis) for individual frequencies (Hz or Hertz on the horizontal axis). The range frequencies tested (pure tones) is usually 250Hz – 8 KHz. This is the range of frequencies which is important for speech recognition.
Conductive Loss
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Sensorineural Loss
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Mixed loss
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Speech Audiogram:
This is a graph which shows the percentage of correct words repeated on the vertical axis against the presentation level (volume in dB). There is usually close correlation between the speech audiogram and the pure tone audiogarm.
Tympanometry:
Is another test performed routinely, especially in younger children. This is a measure of middle ear and Eustachian tube function. It is not usually considered a measure of hearing but rather it measures the mechanical function of the the middle ear which includes the ear drum and the three ossicles (tiny bones) as well as the ventilating adequecy of the Eustachian tube (for the middle ear to work normally it needs to be filled with air at the same pressure as the outside atmospheric pressure ar any given time including different altitudes).
Other Tests:
Include electrophysiological measurement of the auditory system as well as Central Auditory Processing which tests how auditory information is processed, it tests ‘what the brain does with what it hears’.
More specific information about your hearing loss can be obtained by having a comprehensive hearing test. Your Audiologist is the best person to see who will conduct a series of tests and who will also make further recommendations if necessary, such as seeing your family Doctor and/or an Ear, Nose and Throat specialist (ENT). If a hearing aid is indicated this will also be discussed with your Audiologist or Audiometrist.
Common causes of hearing loss in adults are:
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Age
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Noise (work and recreational)
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Infections
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trauma
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Systemic diseases like diabetes
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Genetic
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Idiopathic, cause not known but which results in degeneration usually of the cochlea (inner ear)