Audiometry

Hearing tests are carried out for two main reasons:

  • as a routine part of a baby's or young child's developmental checks
  • to check the hearing of someone who is experiencing hearing problems or has a hearing impairment

How the ear works

The ear is a highly sensitive organ that allows you to hear. It is composed of three parts:

  • the outer ear
  • the middle ear
  • the inner ear

Sound enters the outer ear and passes down the ear canal to the eardrum (a thin layer of tissue that separates the outer ear from the middle ear). Sound makes the eardrum vibrate as it travels into the middle ear.

The middle ear is an air-filled cavity between the eardrum and the inner ear. It contains three tiny bones that are commonly known as:

  • the hammer (malleus)
  • the anvil (incus)
  • the stirrup (stapes)

These bones pick up and carry the sound vibrations from the eardrum to the inner ear.

The inner ear contains the cochlea (a fluid-filled chamber that is responsible for hearing) and the vestibular system (the balance organ). Vibrations travel in the fluid of the inner ear and stimulate tiny nerve endings in the cochlea, which turn the vibrations into electrical signals that are fed along the auditory nerve to the brain.

Hearing problems

Your hearing may be affected if there is a problem with any part of your ear, such as a blockage in your ear canal or an infection of your outer ear (otitis externa) or middle ear (otitis media). This type of outer or middle ear hearing loss is known as conductive hearing loss, wher the sounds are unable to reach the inner ear hearing organ even though it is working normally. Hearing loss of this type may be temporary and reversible.

If sounds reach the inner ear but are still not heard, the fault lies in the inner ear or, rarely, in the hearing nerve. This is called sensori-neural hearing loss. Inner ear hearing loss may occur for a number of reasons, most commonly as a result of age-related change. Inner ear hearing loss is usually permanent.

Rarely, people are born with an inner ear hearing loss. Approximately 1 in 1,000 babies are born with a permanent inner ear hearing loss.

Hearing tests

Hearing tests are painless procedures. A number of different hearing tests are used to check how well the ears are functioning and their ability to detect different levels of sound. Two tests that are often used to check the hearing of babies are the:

  • otoacoustic emissions test (OAE)
  • auditory brainstem response test (ABR)

For older children and adults, a piece of equipment called an audiometer is usually used to test hearing. This test is called an audiogram and it records how well you can hear different pitches sound.

In the past, many children born with a permanent hearing impairment were not diagnosed until they were 18 months or older. However, late diagnosis of hearing loss can be detrimental to a child's language development, social skills and self-confidence.

Because of the need to identify hearing problems early,the HSE Newborn Hearing Screening Programme has started in some areas of the country. After your baby is born, they will be given a number of routine health checks. If your baby is born in Dublin, the Northeast, the Midlands, Cork, Kerry, Kilkenny, Tipperary, Wexford or Waterford, they will be offered a hearing test soon after birth as part of the new screening programme.

Sometimes, premature babies pass this test but are still felt to be in a high-risk group for hearing loss (which in these babies can come on in the first few months of life, rather than from birth). Therefore, they may be given another hearing test when they are between six and eight months old.

There will also be further opportunities to check your child's hearing as they get older. For example:

Babies may have a hearing check as part of the routine developmental check performed around seven to nine months of age.In addition:

  • a child may have their hearing checked as part of their general review when they are about two-and-a-half years old
  • Children may have a hearing test when they are between four and five years old soon after school entry.
  • your GP can arrange for your child to have a hearing test at any age if you feel that their hearing is not right (see below)

The age at which routine tests or assessments are carried out may vary between different areas. Your GP or public health nurse (a qualified nurse who helps families with young children) should be able to advise you.

Newborn Hearing Screening Programme (NHSP)

It is not easy to identify hearing loss in babies who are too young to have a conventional hearing test (an audiogram). Screening a baby's hearing using an otoacoustic emissions (OAE) test soon after they are born enables hearing loss to be identified at an early stage.

The OAE test is part of the Newborn Hearing Screening Programme (NHSP) and will be carried out within the first few days following birth. The hearing test will take place in the hospital maternity unit. If you live in Cork,Kerry,Waterford or Wexford and are not offered a screening test for your baby, you should ask your midwife, public health nurse or GP to arrange one.

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Reporting problems to your GP

If you think your child may have a hearing problem, take them to see your GP as soon as possible. As well as the routine hearing checks mentioned above, hearing tests can be used at any time to help diagnose or rule out other health conditions.

Many children who experience hearing problems turn out to have a very common temporary condition called glue ear, which is where mucus blocks the middle ear. Less commonly, there may be other explanations for a child's hearing difficulties, such as behavioural problems such as attention deficit hyperactivity disorder (ADHD), which is a group of behavioural symptoms that include inattentiveness, hyperactivity and impulsiveness.

Adult hearing tests

Adults who are concerned that they are losing their hearing may also request a hearing test. There are many reasons why adults might lose their hearing other than simple age-related changes, such as ear infections or prolonged exposure to excessive noise.

You should visit your GP if you experience hearing loss in one or both ears, or if you have:

  • tinnitus - ringing or buzzing in your ears
  • vertigo - dizziness or loss of balance
  • severe ear pain that lasts for more than 24 hours
  • discharge - fluid or blood coming out of the ear

You may also need to have a hearing test if you have a head injury, because it could damage your inner ear.

Approximately 1 in every 1,000 babies are born with permanent hearing loss in one or both of their ears. In around half of these children the hearing loss is determined by their genes, even if no other family member is affected.

Early development

Hearing is very important for a young child's early development because it plays a crucial part in their speech and social skills. Therefore, hearing impairment needs to be identified as soon as possible so that appropriate support can be provided for the child and their family.

Young children who have a significant hearing impairment can be given additional help and support with their education.

Hearing deterioration

As you get older, it is likely that your hearing will begin to deteriorate. This is because as you age, the nerve endings in your inner ear are slowly lost and are not replaced.

Hearing loss in old age is usually a gradual process and begins with difficulty hearing other people clearly, particularly when there is a lot of background noise, such as in pubs or when the television is on.

Adult hearing tests

As hearing deteriorates gradually, at first you may not realise that you have a hearing impairment. Other members of your family may be the first ones to notice that you have a problem.

If you are at all concerned about your hearing, you should ask your GP to arrange for you to have a test. A piece of equipment known as an audiometer will be used to check your hearing. If hearing loss is confirmed, you may need to have other tests to identify the cause.

Your GP will also carry out a physical examination of the outside of your ear. They may refer you to either an audiology department or to the ear, nose and throat (ENT) department of your local hospital. In a minority of cases, the specialist will carry out further tests, which may include a scan of your inner ear and hearing nerves.

Investigating hearing problems

Some types of hearing problems are permanent. These include:

  • permanent childhood hearing impairment (PCHI) - hearing problem that a baby is born with or is acquired during childhood
  • age-related deafness
  • deafness that is caused by damage to the inner ear or hearing nerve, which may be the result of an illness or prolonged exposure to very loud noise

Some types of deafness are temporary, such as problems caused by a build-up of earwax or glue ear (fluid in the ear). Glue ear is very common in children but less common in adults. It usually develops along with a cough or cold and clears up after a few days or weeks. Adults who have persistent glue ear should be referred to a hospital specialist to exclude any serious underlying health conditions.

Once the cause of hearing impairment has been identified, the right treatment and support can be put in place. Therefore, as with babies and young children, it is important that your condition is diagnosed as soon as possible.

Older people with permanent hearing loss may benefit from having hearing aids. If you have hearing aids fitted, you will receive advice and support from your local audiology department, including advice about changing the battery, repairs and upgrades.

Having your ears checked

Your GP or practice nurse will first ask you or your child about any symptoms, including whether there is:

  • pain or discharge (fluid)
  • tinnitus - noise in one or both ears
  • vertigo (dizziness)
  • hearing loss
  • previous, relevant medical problems

If you or your child has a hearing problem, your GP or practice nurse will do an ear examination. If they have concerns, they may refer you to an ear, nose and throat (ENT) specialist for further assessment.

Your ear will be examined using an instrument called an auriscope, which is sometimes also known as an otoscope. An auriscope is a small hand-held torch with a magnifying glass used to examine the eardrum and the passageway that leads to it from the outer ear.

An auriscope can be used to look for:

  • discharge - fluid coming out of the ear
  • a bulging eardrum - indicating that there is infected fluid in the middle ear
  • a retracted eardrum - indicating uninfected fluid in the middle ear (glue ear)
  • perforated eardrum - a hole in the eardrum, with or without signs of infection
  • earwax or foreign bodies that might be blocking the ear

Childhood hearing tests

The various hearing tests that are carried out during infancy and childhood are outlined below. Until newborn screening is fully introduced, the infant distraction test (IDT) will continue to be carried out bypublic health nurses to test a baby's hearing at the age of around eight months. Once newborn hearing screening is completely rolled out the IDT will be discontinued.

During the IDT, an examiner sits in front of the infant and uses a ball or a toy to gain their attention. A second examiner, sitting behind the infant then makes a noise at the infant's ear level on either side. If the infant's hearing is working normally, they should turn towards the sound.

The IDT can only be used to make a diagnosis when a child is old enough to turn their head. Healthcare professionals realised that a more accurate hearing test was needed that could be carried out on newborn babies. This led to the Newborn Hearing Screening Programme being set up. At present this is available in three quarters of the country and the intention is to make it available everywhere in 2013.

Newborn Hearing Screening Programme

When newborn babies are tested as part of the Newborn Hearing Screening Programme (NHSP) the automated otoacoustic emission (AOAE) screening test is the hearing test that is used. The test is carried out by a trained hearing screener.The various hearing tests that are carried out during infancy and childhood are outlined below. Until newborn screening is fully introduced, the infant distraction test (IDT) will continue to be carried out bypublic health nurses to test a baby's hearing at the age of around eight months. Once newborn hearing screening is completely rolled out the IDT will be discontinued. During the IDT, an examiner sits in front of the infant and uses a ball or a toy to gain their attention. A second examiner, sitting behind the infant then makes a noise at the infant's ear level on either side. If the infant's hearing is working normally, they should turn towards the sound. The IDT canonly be used to make a diagnosis when a child is old enough to turn their head. Healthcare professionals realised that a more accurate hearing test was needed that could be carried out on newborn babies. This led to the Newborn Hearing Screening Programme being set up. At present this is available in three quarters of the country and the intention is to make it available everywhere in 2013.

Automated otoacoustic emissions test

The AOAE test is a simple, painless test that produces immediate results and can be carried out while the baby is asleep. It involves placing a small probe into the baby's ear which produces a gentle clicking sound. In normal hearing, some of the nerve endings in the cochlea (inner ear) automatically produce a noise of their own as a reflex when a sound is heard. This is often known as cochlear echo.

A cochlear echo will not be produced when the hearing is impaired. This makes the AOAE test a good hearing test. However, it is not totally reliable because sometimes no echo is produced even when a baby has normal hearing. Also, an echo may occasionally be produced when a baby's hearing is impaired, and a baby who is born with normal hearing may go on to develop loss of hearing during their first year.

However, despite not being perfect, the AOAE test is much better than IDT screening, and nowadays far fewer children with hearing loss are diagnosed late (older than 12 months).

Before your baby has the AOAE test, the hearing screener will explain the test to you. If the first test does not produce a clear result, your baby will be given a second test. However, an unclear test result does not necessarily mean that your child has a hearing impairment. It may be that conditions during the first test were not right, such as there being too much background noise.

Automated auditory brainstem response test

If two AOAE test results are unsatisfactory, an automated auditory brainstem response (AABR) test will be recommended for your child.  In certain situations - for example, where a baby has spent a long period of time in a neonatal intensive care unit - they may be given an AABR test and an AOAE test as a matter of routine. The AABR test can be used to provide more information about the baby's hearing.

An AABR test takes around 20 minutes to perform. Three sensors will be placed on your baby's head and neck to detect how their ears, hearing nerves and brain respond to sound. Sounds will then be played through earphones and a computer will be used to record your baby's responses. If their response is strong, it is unlikely that they have any hearing loss.

Like the AOAE test, the AABR test is not totally foolproof. If the result of the AABR test is satisfactory, your baby has good hearing and there is usually no need for further tests. However, an unsatisfactory AABR does not always mean that your baby has hearing loss, but that a further test is needed - an auditory brainstem response (ABR) test.

Auditory brainstem response test

After having an unsatisfactory AABR test, the next step is to carry out an auditory brainstem response (ABR) test. Unlike an AABR test, an ABR test is not an automated test. It is a much more sophisticated and accurate test that is carried out in an audiology clinic by a highly trained audiologist (hearing specialist). The audiologist will also interpret the test results.

Like AABR, the ABR test uses headphones to produce sound and sensors are placed on the baby's scalp and neck. The sensors pick up the electrical signals that are produced in the ears and hearing nerves and a computer turns these signals into a 'wave' that is displayed on a printout or screen.

As sounds become quieter, the waves get smaller and disappear completely when the hearing threshold is reached (when a sound is so quiet that you cannot hear it). Different types of ABR test can be performed to give information about the baby's hearing at different sound frequencies and to determine whether a hearing loss is conductive or sensori-neural.

ABR tests are not used on every baby because they take about 45 minutes (and sometimes longer) to carry out. It therefore would not be practical to use the test for every baby, and the AOAE and AABR tests are used because they are simpler screening investigations, rather than in-depth examinations. 

Again, even if an ABR test is unsatisfactory, it does not always mean that your baby has permanent hearing loss - for example, they may have a temporary blockage due to glue ear.

As well as the hearing tests described above, there are also a number of other tests that may be used at different stages of your child's development. These are described below.

Visually reinforced audiometry

Visually reinforced audiometry (VRA) has replaced the infant distraction test (IDT) as the best way of checking a  baby's ability to react to the direction of sound.

During VRA, the baby sits on their parent's lap and a tester stands in front to keep the baby's attention. Another tester, positioned outside of the baby's visual field, makes a number of different sounds. If the baby reacts by turning their head in the direction of the sound, they will be rewarded by seeing a small toy positioned at the side of the room, which either lights up or moves.

The reward is controlled by the testing audiologist and is only given to the baby if they turn their head in response to a sound. Nothing will happen if the baby turns to try to see the toy without a sound being made. Only rewarding the baby when they turn towards the sound reinforces their response and makes VRA a much more accurate test than the IDT.

Pure tone audiometry

Pure tone audiometry (PTA) tests the hearing of both ears and can usually be carried out when a child is over four years of age. PTA is the type of test carried out when a child starts school.

During PTA, a machine called an audiometer is used to produce sounds at various volumes and frequencies. The child being tested listens to the sounds through headphones and responds when they hear them by pressing a button.

In your child fails a pre-school audiogram, they may be referred to the ENT or audiology department of your local hospital for further testing.

Other childhood hearing tests

Other hearing tests that your child may have at the audiology department of your local hospital are briefly described below.

Play audiometry

Play audiometry involves your child listening to a sound and being asked to perform a simple task as part of a game to indicate that they have heard the sound. This is used for children who are too old for VRA but are not yet able to cope with a pure tone audiogram.

Speech perception test

The speech perception test, also sometimes known as a speech discrimination test or speech audiometry, involves testing your child's ability to hear words without using any visual information. The words may be played through headphones or a speaker, or spoken by the tester.

Sometimes, the child is asked to listen to the speech sounds in the presence of a controlled level of background noise (speech in noise testing) - for example, to mimic the situation in a classroom.

Whispered voice test

The whispered voice test can be carried out on older children in a quiet room - for example, at a GP surgery. See adult hearing tests (box, left) for more information about how the test is performed.

Impedance tympanometry

The eardrum should ideally allow as much sound as possible to pass into the middle ear. If sound is reflected back from the eardrum, hearing will be impaired (or impeded). Fluid in the middle ear will impede sound. Impedance tympanometry measures the 'impedance' of sound by the eardrum.

During impedance tympanometry, a small tube will be placed at the entrance of your child's ear and air will be gently blown down it into their ear. The test can be used to confirm whether your child has glue ear.

With increasing age, your hearing will gradually begin to deteriorate. As you get older, the nerve endings in your inner ear are slowly lost.

Adult hearing tests

As well as pure tone audiometry, speech perception and tympanometry, a number of additional tests may be used to test the hearing of adults. These are briefly described below.

Whispered voice test

The whispered voice test is a very simple hearing test. It involves your GP or practice nurse blocking one of your ears and testing your hearing by whispering words at varying volumes. You will be asked to repeat the words out loud as you hear them.

Tuning fork test

A tuning fork produces sound waves at a fixed pitch when it is gently tapped. Tuning forks are usually used to tune musical instruments.

To test your hearing, the tester will tap the tuning fork on their elbow or knee to make it vibrate, before holding it at each side of your head in turn. At first, the tuning fork will be held in the air, next to your ear, and then against the bone behind your ear (the mastoid bone). This is called a Rinne test and it can help to determine whether there is a middle ear (conductive) or inner ear (sensori-neural) pattern of deafness.

The tuning fork can also be placed on the centre of your forehead or on the bridge of your nose. Whether the sound is heard in the good or bad hearing ear can also help to distinguish between the two types of hearing loss. This is known as a Weber test.

Bone conduction test

A bone conduction test is often carried out as part of a routine pure tone audiometry (PTA) test, although it may not be suitable for very young children.

Bone conduction involves placing a vibrating probe against the mastoid bone behind the ear. It tests how well sounds that are transmitted through the bone are heard. Bone conduction is a more sophisticated version of the tuning fork test, and when used together with PTA through headphones (air conduction), it can help to determine whether hearing loss comes from the outer and middle ear, the inner ear, or both.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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