evaluation of hearing

1. Assessment of hearing
Dr safika zaman , PGT , DEPT OF ENT & HEAD NECK SURGERY
RKMSP,VIMS

2. Key facts of WHO data published on 1st
March 2020
Around 466 million people worldwide have disabling hearing loss , and 34
million of these are children.
It is estimated that by 2050 over 900 million people will have disabling
hearing loss.

3. History taking
patient’s perception of the degree of hearing loss,
unilateral or bilateral,
onset
progression
fluctuating, or stable.

4. Significant associated symptoms with
hearing loss
aural fullness,
tinnitus, vertigo, disequilibrium,
otalgia, ear discharge
headache, visual problems, and other neurological complaints (facial
numbness or weakness, ataxia, ).
 Past history of head trauma, noise trauma ,ototoxic drug ,
systemic illness , family history of hearing loss, etc.

5. Examination of Ear
 complete head and neck examination.
 auricle and the post auricular area should be examined for
deformities, surgical incisions.
 presence of a hearing aid.
 patency of the EAC.
 Tympanic membrane status.

6. Functional Examination
 1. Voice test- a. Wispered voice. b.Conventional voice
 Tunning fork test
 Audiometric tests

7. Voice Tests
 Simple
 Screening
 Limitation: a. variable surrounding acoustic condition.
b. Inter-parson variability of loudness of voice.
c .lower sensitivity in children.

8. Pirozzo S, Papinczak T, Glasziou P. Whispered voice test for screening for hearing
impairment in adults and children: systematic review. BMJ. 2003;327(7421):967.
doi:10.1136/bmj.327.7421.967

9. Tuning fork tests
 Mainly are 1. Rinne’s test
2 .weber test
3.Schwabach test
4. Absolute Bone conduction test

10. Rinne’s test
 Compares bone conduction with air conduction.
 A conductive deafness of more than 25 dB usually gives a negative
Rinne`s test with 512 Hz.

11. Weber test
 This is valuable in
unilateral
deafness

12. Pure tone audiometry
 Aims are-
 1. whether the subject has any definitive hearing loss.
 2. Its conductive sensorineural or mixed.
 3. If sensorineural , then whether it is cochlear or retro-cochlear
 4.The degree of hearing dysfunction

13. Pure tone Audiometer

14. Preparation of pure tone audiometry
 Calibration of the Instrument.
 A reasonably noiseless test
environment
 Proper positioning of
headphones & bone vibrator.
 Thoroughly explained
instruction to the patient.

15. Measuring AC
 Method

16. Technique of bone conduction testing
 1. Mastoid placement of the bone conduction
vibrator:
The tension of spring headband -500gm/sq cm.
Region should be free from hair
Constant tone is presented.
Searching for most sensitive point.
Masking of opposite ear
Taking measurement for bone conduction.
2.Frontal placement:
superior technique regarding consistency of
result.
less sensitive area.

17. Problems in BC Audiometry
 Wrongly elevated thresholds due to entry of ambient noise from
environment.
 Possible up to 40 dB at 250hz, 50 dB at 500 hz60 dB at 1000hz.
 Difference in skull skin thickness.
 Different sensitivity of sound in different area of mastoid.
 Improper masking of non test ear.
 Occlusion effect if EAC is blocked by air conduction headphone.

18. Masking
 Why do we mask?
Because, vibrator send impulse to both
ear during BC test & in AC sound of 50
dB and above likely to cross and
stimulate the other ear.
Goal of masking in PTA is to evaluate
each ear independently. So we block the
other ear acoustically by presenting a
noise

19. When to mask?
 In case of Air conduction
AC(test ear)-BC(non test ear)>
inter-aural attenuation.
Value of inter-aural attenuation for AC is
approxmately 50 dB
In BC the value of inter-aural attenuation
may be zero dB, so ideally non test ear
should always be masked.

20. How much to mask?

21. Sounds used for masking
 White noise: equal amount of sound of all frequencies.
 Narrow band noise: 100 Hz to 200 Hz below or above the test
frequency.
 Complex noise: low frequency fundamentals plus the multiples of
that frequency up to 4000Hz.
 Masking efficacy is best with narrow band noise.

22. Grading of deafness

23. Interpretation of Audiograms
 What we need to know from a Audiogram?
AC Threshold
BC threshold
A-B gap
Masked or non- masked
We must see, if the audiogram is matching with the clinical findings
and tuning fork test.

24. Normal Audiogram

25. Conductive deafness
AC> 30 Db
BC< 20dB
A-B Gap> 25dB

26. Sensorineural deafness
AC> 30 dB
BC>20 dB
A-B Gap < 20 dB

27. Mixed deafness
AC > 45dB
BC>20 dB
A-B Gap >20 dB

28. Limitation of PTA
 Subjective test
 Improper masking
 Faulty placements of headphones and vibrator
 Occlusion effect during BC
 Noisy environment
 Improper calibration of audiometers
 Proper application of tension on headband
 Improper examiner

29. Tone decay test
 Wedensky’s peripheral nerve inhibition theory:
It says in a narcotized nerve , if impulses are presented very rapidly
only few impulses will pass successfully, but the later ones will fail
to pass through the narcotized sections.
Pathology in the auditory nerve causes an abnormally rapid
deterioration in hearing, if a tone is presented continuously.
Most popularly done by Carhart’s method.

30. Tone decay test
 A tone whose intensity is only slightly above their absolute
threshold of hearing can be heard continuously for 60 seconds.
 The number of dB above the patient's absolute threshold of
hearing that are required for the tone to be heard for 60 seconds.
 A decay of between 15 and 20 decibels is indicative of cochlear
hearing loss. A decay of more than 25 decibels is indicative of
damage to the vestibulocochlear nerve .
 TDT helps in diagnosing neural lesions like Acoustic neuroma and
Auditory neuropathy.

31. Tone decay test

32. Short increment sensitivity index(SISI) TEST
 SISI tests the ability to recognise 1dB increases in intensity of
pure tones presented 20dB above the pure tone threshold for the
test frequency.
 It can be used to differentiate between cochlear and retro
cochlear disorders.

33. Interpretation
A patient with a cochlear
disorder will be able to perceive
the increments of 1dB,(70% to
90% score) whereas a patient
with a retro cochlear disorder will
not(0 to 25%)
Score between the two do not
have much diagnostic value.

34. Speech Audiometry
 Valuable test for therapeutic and rehabilitative purpose.
 It comprises of –
Speech reception threshold: lowest hearing level in dB.
Speech discrimination score: percentage of correctly
identified words.
Phonetically balanced word list: monosyllabic words.
words must be covered in patients language.
Normal score is 90 to 100%.
In neural loss SDS is low.

35. Component of Impedance Audiometry
1. Eustachian tube function tests
2. Tympanometry
3. acoustic stapedial reflex tests

36. Tympanometry
 Principle:
measurement of
compliance with
changing pressure.

37. Tympanogram
 Normal static compliance: 0.35 to
1.40 ml.
 Baseline compliance value
measured at +200 mm of water
pressure.
 In most cases pressure change is
minus 400 to + 200dapa.
 Most accepted normal pressure
range is + 50 to -50 mm of water
pressure.

38. compliance
 Acoustic compliance is an expression of the ease of movement of middle ear system.
It is reciprocal of stiffness.
Increased compliance: 1. chain discontinuity.
2.scared TM. Normal compliance: ET block
3.very large TM.
4.post-stapedectomy ear.
Decreased compliance: 1.otosclerosis.
2.secretory otitis media
3.tumor in middle ear.
4. fixed malleus
5.tympanosclerosis.

39. Middle ear pressure
 Negative pressure: 1. blocked ET.
2.OME
Normal pressure: 1. otosclerosis
2.ossicular chain discontinuity.
3.scarred TM
4.fixed ossicles.
Positive pressure: early AOM
Absence of peak pressure: 1. adhesive otitis media.
2.perforation of TM
3. grommet in situ
4.cerumen/artefact

40. J. Jerger types

41. Graphs

42. Fallacies of the tympanometry test
 If two types of middle ear pathology present together , graph may
mask one of them. example-
otosclerosis & tubal blockage – B Graph
scared TM & otosclerosis – Ad graph
normal middle ear with thick TM-As graph
micro perforation- normal volume flat curve
thick TM with ossicular discontinuity- normal
graph
Thus tympanometry is never a stand alone test

43. Eustachian tube function test
 William’s test : done when
TM is intact.

44. Toynbees test
 Done in case of perforated
TM.
 Impedance audiometer
artificially changes pressure.
 If some residual pressure
persists even after 5
swallows tubal function
considered as compromised.

45. Acoustic reflex test
 Helps in-
1. Elimination of middle ear pathology
2. Differentiate between cochlear and retro-cochlear pathology.
3. Detection of some brainstem pathology.
4. Identifying the level of lesion in facial nerve paralysis.

46. The model of acoustic reflex pathway

47. Causes of absent efferent side reflex
 Lesion in the facial nerve nucleus
 Lesion in the FN Proximal to nerve to
stapedius, in condition like Ramsay
hunt syndrome.
 Disease of stapedius muscle like
myasthenia gravis
 Middle ear lesion like , otosclerosis,
atelectasis.

48. Brain Stem Evoked Response
Audiometry(BERA)
This is an objective electrophysiological
test of auditory system.
This test ascertains the structural and
functional integrity of the auditory system.
Non invasive test.
Cant asses the conscious perception of
hearing.

49. Indication of doing BERA
 Detection and quantification of
deafness in difficult to test
patients.
 Objectively determining the
nature of deafness;
 Identification of site in retro-
cochlear pathologies.
 Study of central auditory
disorders by associated test like
MLR and LLR.
 Study of maturity of CNS.

50. Principle of BERA
 When sound reaches the
cochlea , it is converted into an
electrical response, and passes
to auditory cortex. BERA is
one of the many auditory
evoked potentials that can be
recorded from the brain.
Auditory evoked potential can
be recorded upto 500 milisec.
Early 10 milisec of this
response is called BERA.

51. Neural pathway & wave
generation

52. procedure
1.The person is made to lie back on
a reclining chair or on a bed and is
asked to remain still. For infants, it
is usually done when they are
sleeping or sedated.
2.Stimulus is given in the form of
a click sound or tone pip, via an
ear phone or head phone. The
stimulus is of varying loudness
and of the frequency range from
1000 to 4000 Hz

53. Cont…
3.The waveforms are produced at the brainstem.
4.recorded by the electrodes that are placed over the scalp at various places.
 Non-inverting electrode over the vertex.
 Inverting electrodes on each ear lobe or mastoid.
 Earthing electrode over the forehead.
5.waveforms are amplified.
6.Various readings in different positions and polarities are recorded and marked.

54. Electrical system

55. Normal BERA GRAPH

56. Parameters to study from BERA
 1. latency of waves- absolute, inter wave and inter aural.
 2. Absolute and relative amplitude
 3. wave form morphology.
 4.Latency-intensity functions of wave Ⅴ.

57. Normal values and criteria for abnormality
in BERA

58. Clinical uses of BERA
 Estimation of hearing threshold:
useful in difficult to test subjects, the degree of hearing impairment
is usually assessed by gradually decreasing the intensity of sound
stimulus and noting the morphology of the graph until the wave v is
no longer identifiable.

59. Normal & hearing impairment graph

60. Nature of deafness- conductive, mixed ,
sensory or neural
 We asses by
analysing a Latency-
Intensity function
curve.
 In CHL the graph
shifts above , but
more or less parallel
to a normal graph.
 In SNHL the graph
shows shallow
configuration.

61. Profound hearing loss

62. BERA changes in acoustic neuroma

63. Other BERA changes
 Increase in ⅲ to ⅴ suggests lesion in rostral brain stem like
demyelinating disease.
 Absence of four and five with presence of one and three suggests
of intrinsic brain stem lesion.

64. Oto acoustic Emissions(OAE)
 Oto acoustic emissions are biological
phenomena generated in normal cochlea,
when mechanical activity takes place in
outer hair cells.
 `This is sound energy and measured in
deciBels.
 non invasive test.
 Screening test for newborn.

65. Basis of OAE
The biological activity of the cochlear amplifier in the form of movement of the OHC
and the hair cell bundle generates a noise or mechanical activity , this signals are
picked up by the sensitive microphone.
The presence of robust OAE is an indication , of presence of healthy OHCs.
Presence of OAE is also proof of presence of functioning middle ear.

66. Types
 Spontaneous OAE(SOAE)
 Stimulus frequency OAE(SFOE) :in response to a pure tone.
 Transient-evoked OAE(TEOAF): elicited by presenting a brief
transient sound.
 Click evoked OAE(COAE): click is a mixture of sound, so activates
entire length of cochlea.
 Distortion product OAE(DPOAE)

67. Distortion product OAE(DPOAE)
 The basis is when two pure
tones are presented together,
the waves interact on the
basilar membrane, generates
several new sounds, that are
different from the two pure
tone.

68. Interpretation of graph

69. Limitation of OAE
 Major drawback is it can only suggest , but not
confirm the possibility of hearing impairment and
can not distinguish between mild moderate and
severe hearing loss when OAE is absent.
 Depending upon the ambient room environment and
physiological noise, floor noise will be variable, this
will obscure the generated OAE, and will produce
variable result for the test.

70. Auditory steady state response(ASSR)
 this is an evoked potential test can be used to objectively predict
frequency specific hearing threshold in all patients.
 Principle: in ASSR the stimulus is presented to ear in very rapid
interval, if stimulus rate is sufficiently rapid , the resulting
response resembles a sinusoidal wave, this response is analysed
by automated spectral analyser , thus helps us to derive objective
PTA.

72. Graphical representation of ASSR

73. summary

74. summary