Tag Archives: tests of hearing

How hearing impairment is diagnosed in infant and young children?

Hearing loss can range from a mild impairment to profound loss. Conductive hearing loss is largely preventable and can be managed by medicine/surgery. Sensor neural hearing loss may need fitting with hearing aids.

Early identification of hearing loss in newborn and young children is of critical as he develops language and speech by hearing to his surroundings.

In general neonates and infants could be tested by BERA, children in the age group of 2 – 3 yrs could be screened using free – field audiometry, children above 4 yrs could be conditioned and then a audiometry can be performed to test hearing impairment.

Babies should be screened for hearing at birth especially high risk ones.

Child with mild hearing loss is generally labeled as inattentive or slow learner. Hearing should be tested as child grows at any time on slightest suspicion of hearing deficit by Parents, care givers, teachers and family doctors.

Screening for hearing has been done for many years but still does not detect hearing impairment as early as desirable. Mother’s instinct for her child is usually correct even at early age and should not be neglected.

The type of tests used to identify hearing loss depend on the age of the child, and include:

* Behavioural observation audiometry (BOA) – for babies less than seven months of age.

It consists of making noises, such as shaking a rattle close to ear, and then observing the baby’s response.

* Distraction method – it is formalized method of behavioral observation audiometry for children 7-19 months.

Infant sits on mother’s lap and one tester standing in front uses toys to raise attention. Other tester behind the child presents signals like shaking a rattle, or drum beat. First tester observes the child’s response. Response may be head turn, eye turn, frowning, sucking etc. After each response the signal intensity used to elicit a response is measured.

* Visual reinforcement orientation (VRA) – useful for children 7-30 months of age. The baby is taught to move their head towards sound by pairing it with an interesting visual stimulus, located in the direction of the speaker.  Their response to different sounds can then be measured. Test is done in sound proof room with speaker and headphone. The ears can be tested individually if the baby tolerates headphones.

* Performance audiometry test – older children are taught to respond to sounds by a performing a simple action or playing a game, such as dropping a marble when they hear the sound.

* Oto-acoustic emission – certain sounds generated by the inner ear can be recorded to check the function of the tiny hair cells in the cochlea.

* Auditory brainstem response testing – to check the electrical activity in the brain in response to a sound. Electrodes are placed on the head to measure the brain waves. It is most popular test for neonatal hearing assessment and for detection of hearing loss.

* Transtympanic Electrocochleography – to check the cochlea for signs of electrical activity in response to sound. It is better indicator of hearing threshold than any other auditory evoked response in children. An electrode is threaded through the eardrum to touch the cochlea and it requires general aneasthesia in children.

* Impedance audiometry or Tympanometry – a probe which snugly fits into the ear and air is pumped into the ear canal. Neonates and young infants may be examined so long as the probe tone is 660 Hz and not 220 Hz. Stapedius reflex are used to assess middle ear disfunction. Impedance audiometry is not an alternative to behavioral audiometry.t

** Hearing test for older children are same as for adult

Tests of Hearing

Tests of hearing:-

  • Finger friction test
  • Watch test
  • Speech test; whisper and conversational speech
  • Tuning fork tests
  • Pure-tone audiometry
  • Impedance audiometry / tympanometry
  • Brain-stem evoked response audiometry

Finger friction test, watch test, clinical speech test and tuning fork tests are often used for hearing screening or bed side testing.

Tuning-forks test :

256, 512 and 1024 Hz frequency, vibrating tuning forks are placed in front of ear (to test air conduction), behind the ear and over the forehead (to test bone conduction; here sound is directly transmitted to the cochlea) to get an idea of hearing, and degree & type of hearing impairment if any.

The tuning fork should be struck against elbow or knee, and not against a table or desk to avoid undesirable harmonics.

Result of tuning fork test:

Rinne test described as being positive (normal/conductive deafess) or negative (sensorineural deafness),

Weber test described as being central (normal) or lateralized to one ear (same side conductive loss or other side sensorineural loss; interpreted along with Rinne test)

Schwabach’s test where patients bone conduction is compared with that of examiner’s..

Pure-tone Audiometry:-

Audiometer is an electronic device which produces pure-tones.

Person has to put on headphones and then listen for some different tones from low pitch to high pitch. Person has to push a button or raise hand when he hears each tone.

Hearing is measured at different frequencies from (250 Hz to 8,000 Hz). Results in decibels are charted in the form of graph called audiogram.

This procedure is called Pure-tone Audiometry.

It is a subjective test of hearing and cooperation and understanding of patient is of utmost importance.

Audiometry is required: –

1. To know degree and type of hearing loss.

2. To keep record and for medico-legal purposes.

3. Before prescribing a hearing-aid.

Reading Audiogram:

pure-tone-audiogramFigure 1: An audiogram of an ear with normal hearing

Result interpretation; Reading Audiogram-

Normal hearing: less than 15-25 decibels

Minimal loss: 16 to 25 decibel loss

Mild loss: 26-40 decibel loss

Moderate loss: 41-55 decibel loss

Moderately severe Loss – 56 to 70 decibel loss
Severe loss: 71 to 90 decibel loss
Profound: 91 decibel loss and above
To know the type of hearing loss bone conduction is tested, If hearing is better by bone conduction a conductive loss is present.

Speech audiometry:

Patient’s ability to hear and understand speech is measured.

Certain number of words presented via head phones or free field loud speakers, and person asked to repeat the words.

Speech reception threshold is minimum intensity at which a person is able to repeat at least 50% of words correctly. Here a set of two syllable words with equal stress on each syllable (spondee words) are used.

Speech discrimination score is percentage of words heard correctly when phonetically balanced words at 30 to 40 decibel above the person’s hearing threshold are presented.

A score of 90 – 100% is considered excellent, 80 – 89% is good, 70 – 79% is fair, 60 – 69% is poor, <50% is considered very poor.

Tympanometry or Impedance audiometry –

Objective test of hearing; particularly useful to test hearing in infant and child, to know patency of Eustachian tube, and to know condition of middle ear like presence of fluid or fixation (as in otosclerosis) or dislocation of ossicles.

Ossicles are 3 small bones present in middle ear namely malleus, incus and stapes.

Equipment consists of a probe which snugly fits into external ear canal.

Tymanometry is the dynamic measurement of middle ear pressure through measuring mobility of the tympanic membrane. The resultant changes in air pressure variation are plotted on a graph called tympanogram.

Acoustic reflex testing consists of response contraction of subjecting the ear to a loud sound a rough method of evaluating hearing.

Interpretation of tympanogram:-

types of tympangrams

Fig-2: Different types of tympanograms (pic taken from   http://ivertigo.net/graphics/v14.gif)

The shape of the tympanogram suggests how the eardrum is functioning.

1. Normal eardrum movement is shows a well-formed peak, where height of the peak indicates the amount of eardrum compliance, (type A).

2. A flat line indicates little or no eardrum movement. This type of  tympanogram (type B)is commonly seen when fluid is present behind the eardrum or when there is a hole or perforation in the eardrum .

3. A peak to the left of the normal pressure range (type c) means adequate eardrum movement with negative middle ear pressure, seen in persistent cold or initial phase of fluid accumulation or recovery phase of fluid accumulation.

Reduced mobility with normal middle ear pressure (type As) is seen in otosclerosis.

Normal middle ear pressure with hyper-mobility (type Ad) is seen in disruption of ossicular chain.

Brain stem evoked response audiometry (BERA): –

Auditory brain stem response (ABR) audiometry, Brainstem auditory evoked response audiometry (BAER)

It is a test of neurological activity of auditory nerve and brain stem in response to auditory stimuli.

Electrodes are placed on scalp and ear lobe and patient is asked to relax and remain still .

Clinical uses of BERA

1. It is an effective screening tool for evaluating cases of deafness due to retro cochlear pathology i.e. (Acoustic schwannoma).

2. Used in screening newborns for deafness

3. Used for intra-operative monitoring of central and peripheral nervous system

4. Monitoring patients in intensive care units

5. Diagnosing suspected demyelinated disorders (multiple sclerosis)