Types of Hearing Loss

Hearing Loss can be congenital (present at birth) or acquired (occurs after birth).  Hearing loss is categorized depending on the type of hearing loss.

Conductive Hearing Loss

A conductive hearing loss occurs when there is a blockage or problem in the outer or middle ear.  There is therefore a reduction in the amount of sound from the outer ear that reaches the inner ear or a loss of loudness.  The inner ear functions normally when there is a conductive loss.

Atresia is categorized as a conductive loss because there is a problem conducting the sound from the outer ear through to the inner ear (i.e. there is no canal opening or canal for the sound to travel through).  Other causes of a conductive hearing loss include ear infections, perforated ear drum, ‘glue ear’ (fluid trapped in the middle ear), blockages of the canal caused by impacted wax or foreign objects, cholesteotoma etc.

Sensorineural Hearing Loss

A sensorineural hearing loss occurs when there are problems in the inner ear.  This is when the cochlea (sensory part) or auditory nerve (neural part) is damaged or malfunctions.  This type of hearing loss results in loss of loudness as well as lack of clarity.

Causes of a sensorineural hearing loss include inherited hearing loss, diseases such as meningitis, viral infections, birth trauma, premature birth complications, excessive noise exposure, drugs which can damage hearing, head injuries etc.

Mixed Hearing Loss

A mixed hearing loss is when there is a combination of both a conductive loss and a sensorineural loss.  This occurs when there is a problem conducting the sound from the outer ear to the middle ear as well as a problem in the inner ear.

An example of a mixed loss would be a child with atresia who also has a sensorineural loss caused by meningitis.

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Degrees of Hearing Loss

The loudness or level of sound is measured in decibels (dB).  Hearing loss is measured in decibels, but usually described in terms of the degree of hearing impairment.  The degrees of hearing loss are classified as mild, moderate, severe or profound.

Normal Hearing (0dB – 20dB)

If hearing thresholds are up to 20dB then hearing is within normal limits.

Mild Hearing Loss (21dB – 45dB)

A mild hearing loss would result in difficulty hearing soft speech & conversations

Moderate Hearing Loss (46dB – 65dB)

A person with a moderate hearing loss would have difficulty understanding conversational speech, especially when there is background noise.

Severe Hearing Loss (66dB – 90dB)

Normal conversational speech is inaudible for people with a severe hearing loss.  The clarity of speech is also likely to be affected.

Profound Hearing Loss (91dB +)

For a person with a profound hearing loss, a sound must be close and very loud for them to be able to hear it.  Normal conversational speech is inaudible.

 

Refer to Australian Hearing’s Frequency and Intensity of Familiar Sounds publication for more information.