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There are three types of hearing loss, sensorineural, conductive or mixed.
Sensorineural hearing loss relates to damage to the hair cells in the inner ear, auditory nerve or brain. Sensorineural hearing loss can be caused by: exposure to loud noises, ageing, meningitis, viruses, genetic factors, certain drugs, certain pre-natal conditions. Usually sensorineural hearing loss is permanent. People with sensorineural hearing loss can be helped with amplification (hearing aids).
Conductive hearing loss relates to a problem in the transmission of sound through the outer and middle ear. Conductive hearing loss can be caused by: wax blockage, perforated eardrum, various forms of otitis media (OM), otosclerosis (abnormal growth of bone in the ear), or a break in one of the middle ear bones. Many of the conductive hearing losses can be medically or surgically treated. Some people with conductive hearing loss use amplification.
Mixed hearing loss involves both conductive and sensorineural hearing loss.
Audiology is the study of hearing, balance and related disorders.
Children with recurrent, persistent and chronic OM conditions for more than 3 months should be seen by an audiologist.
It is the audiologist’s job to work out if a patient has a ‘normal range’ of hearing. A person may have normal hearing or slight, mild, moderate, moderately severe or profound hearing loss.
Understand conversation at 3m
Mild (26 -40db)
Understand conversation at 1-1.5m
Moderate (41 – 55db)
Understand conversation at 0.5m
Moderately severe (56-70db)
May understand speech at 25cm
Severe (71 – 90dB)
May understand speech at <15cm
May only be aware of very loud sounds
In a hearing test sounds are played at a particular frequency (pitch) at different intensities (volume) usually increasing from soft to loud. When the person hears the sound they raise their hand or press a button to let the audiologist know they have heard the sound. If the patient can hear the sound 2 times out of 3, the audiologist plots the intensity and the frequency of the sound on an audiogram. The actual values plotted on a audiogram are called ‘thresholds’.
Across the top of the audiogram are numbers representing the frequencies of sounds that are to be tested. Low frequency sounds are on the left and high frequency sounds are on the right. Frequencies are measured in hertz (Hz) or kilohertz (KHz). This audiogram form depicts frequencies in Hz. The range of frequencies on this audiogram match the range of frequencies for general speech. The figure shows the ranges of the different types of hearing loss.
Along the left hand side of the audiogram is the intensity scale in decibels. Softer sounds are represented at the top of the audiogram and louder sounds are at the bottom. ISO stands for International Standards Organisation which is a worldwide association that sets standards for many physical measurements.
Air and bone conduction tests are used to work out what type of hearing loss a person might have. In an air conduction test a child wears ear phones to listen to specific sounds transmitted through the ‘air’. Air conduction tests assess the functioning of the outer, middle and inner ear. In a bone conduction test a small bone vibrator is placed on the mastoid prominence behind the auricle (raised area behind the external ear). The bone vibrator transmits sounds to the bones of the skull which stimulates the inner ear directly. Bone conduction testing assesses functioning of the inner ear only. Comparisons of air and bone conduction thresholds are used to determine the type of hearing loss.
Sensorineural hearing loss is defined as a difference of 15dB or less between the air conduction thresholds and the bone conduction thresholds of a given ear, and the air and bone conduction thresholds are worse (higher) than 15dB.
Conductive hearing loss is when bone conductor thresholds are 15dB better (lower) than air conduction thresholds and the bone conduction thresholds are 15dB or less.
Masking is used to prevent the non-testing ear from hearing the sound tests. An unmasked signal of a high enough intensity presented to the test ear can “cross over” and be heard by the non-test ear. Masking is necessary if there is a 40dB difference in the air conduction threshold of the test ear and the bone conduction threshold of the non-test ear. Masking is almost always necessary when testing bone conduction. Bone conducted sounds are transmitted equally by the bones of the skull to both ears.
There are certain symbols to indicate if test results are from the right or left ear, and whether tests have been masked or not. Sometimes the symbols will be colour coded with red representing the right ear and blue representing the left ear.
Any of the above symbols with an arrow pointing downwards means that there was no response at that frequency.
Most audiograms will contain a key to all the audiometric symbols.
There is some uncertainty about the degree of hearing loss associated with different forms of OM, but it is generally agreed that children with persistent OME, recurrent AOM or a perforation (wet or dry) for more than three months are likely to suffer from significant effects of hearing loss and should be referred to an audiologist and an ear, nose and throat (ENT) specialist. A hearing loss of 35dB or more in the better ear is considered disabling, but even a loss of 20dB occurring during speech development and early schooling may have negative social and educational consequences.
Below are some key questions to ask parents to see if their child has hearing loss.
Do sudden loud noises wake the baby?
Does the baby cry at very loud noises?
Does the baby jump at sudden loud noises like the door slamming or dog barking nearby?
Does the baby sometimes turns its eyes and start to turn its head to see where a noise comes from?
Is the baby distracted from feeding by moderately loud noises close by?
Does the baby turn often turn to straight sounds?
Does the baby make a variety of babbling sounds?
Does the baby enjoy playing with noisy toys or objects?
Can you soothe the baby with your voice?
Does the baby turn to find things heard but not seen?
Does the baby gurgle, coo or babble to unseen sources of voices or other sounds?
Does the baby respond to hearing sounds like the bath running, food being prepared or other children coming home?
Does the baby copy words and sounds?
Does the baby by about 15 months use some single words spontaneously?
Does the baby respond when you call from another room?
Does the child talk in 3 word sentences?
Are you able to have a conversation with the child?
Does the child sit too close to the television?
Does the child respond to you when you call them from a distance or when they have their back to you?
Does your child have trouble listening in noisy places i.e. people chatting in the background?
Parents need to be aware of ways to communicate more effectively with children with hearing loss i.e. speak face to face. Parents also need to be aware of situations where a child’s listening may be affected i.e. people talking in the background. It is important that parents encourage the use of language and speech at home. Reading, writing, singing and telling stories should be encouraged in children. Parents can also help by participating in their child’s learning at child care and preschool.
Children with partial hearing loss can have problems hearing in a noisy classroom. Teachers should try to reduce background noises such as: people talking and moving, outside traffic, air conditioners and building site operations. Children with hearing loss should sit at the front of the classroom and the teacher should try to use as much face to face communication as possible. The use of hands and facial expressions can also be helpful. English is a second language for many Indigenous children. Teachers should be aware of using new words and ideas in English that may be unfamiliar to Indigenous children. Writing key vocabulary on the board and using pictures or objects are useful ways to communicate new ideas. Teachers can also ask other students to help give prompts to children with hearing loss.
Coates H, Vijayasekaran S, Mackendrick A, Leidwinger L, et al. (2008) Aboriginal ear health manual. Perth, WA: Abbott & Co Printers
Darwin Otitis Guidelines Group (2010) Recommendations for clinical care guidelines on the management of otitis media in Aboriginal and Torres Strait Islander populations. Darwin: Menzies School of Health Research
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