audiology and tuning forlk

1. Audiology
part i
Dr Humra
Shamim

2. Evolution of audiology
• Prior to World War II, hearing-care services were provided by
physicians and commercial hearing aid dealers.
• Because the use of hearing protection was not common until
the latter part of the war, many service personnel suffered the
effects of high-level noise exposure from modern weaponry.
• It was the influx of these service personnel reentering civilian
life that created the impetus for the professions of otology
(the medical specialty concerned with diseases of the ear) and
speech pathology (now referred to as speech-language
pathology) to work together to form aural rehabilitation
centers.

3. Some of the earliest tests of hearing probably consisted merely
of producing sounds of some kind-
• such as clapping the hands or
• making vocal sounds
• the ticking of a watch
• the clicking of two coins
These tests provided little information of either quantitative or a
qualitative nature.

4. CLINICAL TESTS OF HEARING
1.FINGER FRICTION TEST
• It is a rough but quick method of screening and consists of rubbing
or snapping the thumb and a finger close to patient’s ear
2. WATCH TEST
• A clicking watch is brought close to the ear and the distance at
which it is heard is measured.
3.SPEECH (VOICE) TESTS
• The patient stands with his test ear towards the examiner at a
distance of 6 m. Eyes are shielded to prevent lip reading and the
non test ear is blocked by intermittent pressure on the tragus by an
assistant. The examiner uses spondee words walks towards the
patient. The distance at which conversational voice and the
whispered voice are heard is measured.
• Disadvantage :lack of standardization in intensity and pitch of voice
used for testing and the ambient noise of the testing place.

5. 4.TUNING FORK TESTS
• The three tuning forks generally used
include : 256 Hz, 512 Hz, 1024 Hz.
• Most common being 512 Hz because
–
 It is present in the mid speech
frequency range
 Overtones are minimal
 Sound is more auditory than tactile in
nature
 Tone decay is optimal.

6. PREREQUISITES FOR AN IDEAL TUNING FORK:
• It should be made of a good alloy
• It should vibrate at the specified frequency
• It should be capable of maintaining the vibration for one full
minute
• It should not produce any overtones

7. Advantages of tuning fork tests
1. Easy to perform
2. Can even be performed at bed side
3. Will give a rough estimate of the patient’s hearing acuity

8. The following tests can be performed using a tuning fork:
1. Weber test
2. Rinne test
3. Absolute Bone Conduction test
4. Schwabachs test
5. Bing test
6. Stenger’s test
7. Gelle test
8. Chimani-Moos test

9. METHODOLOGY OF USING TUNING FORK
• The tuning fork must be struck against a firm surface (rubber pad / elbow
of the examiner). The fork should be struck at the junction of upper 1/3
and lower 2/3 of the fork. It is this area of the fork which is capable of
maximum vibration.
• Vibrating fork should be held parallel to the acoustic axis of the ear being
tested.

10. Bone conduction:
• Cochlea gets stimulated in 3 ways
when bone is stimulated
• The three normal routes of bone
conduction of sound vibrations to the
inner ear:
 route A: via the skull bone;
 route B: via the ossicular chain;
 route C: via the external auditory
canal.
• In a normal ear, when the skull is
vibrated by bone-conduction, it not
only vibrates the cochlea via route A,
but it also vibrates the tympanic
membrane and ossicular chain (route
B) and the air in the external auditory
canal (route C).

11. • In the presence of a conductive
defect, the osseous route A is the
only route for sound vibrations to
reach the inner ear. When there is a
middle ear conductive defect, routes
B and C are materially diminished in
magnitude

12. OUTER EAR COMPONENT OF BONE
CONDUCTION
• The outer ear bone conduction component arises from vibration of
the bony and especially the cartilaginous walls of the outer ear
canal that, in turn, causes sound waves to radiate into the outer ear
canal .These sound waves propagate through the middle ear and
finally to the inner ear.
• The outer ear component may play little role in the normal
unoccluded ear canal, but its role is magnified by the occlusion
effect .Normally the outer ear canal acts as a high-pass filter that is,
high-frequency energy is passed into the middle ear whereas low-
frequency energy escapes through the ear canal opening. Outer ear
canal occlusion traps this low-frequency energy and thereby
enhances bone conduction hearing up to 20 dB in the lower
audiometric test frequencies.

13. MIDDLE EAR COMPONENT OF BONE
CONDUCTION
• The middle ear component of bone conduction is the inertial lag of the
ossicles . Middle ear ossicles are not directly attached to the skull, but are
instead suspended by ligaments and tendons and attached at either end
to the elastic tympanic and oval window membranes. The ossicles are free
to move out of phase with skull vibrations and will do so because of
inertia, much as coffee would lag and spill from a cup moved precipitously.
• Middle ear ossicles vibrate relative to the skull in a like manner as during
air conduction hearing, and thus energy is propagated into the inner ear.
The middle ear component occurs mainly at and above 1,500 Hz and is
especially significant near 2,000 Hz, the approximate resonant frequency
of the middle ear

14. INNER EAR COMPONENT OF BONE
CONDUCTION
• Inner ear bone conduction has been described as resulting from alternate
compressions and expansions or distortions of the bony cochlear capsule.
In turn, cochlear fluids are displaced and basilar membrane-traveling
waves are initiated.
• One factor making cochlear fluid displacement possible is the out-of-
phase and disproportionate yielding of the round and oval cochlear
windows, which creates alternating spaces for fluid displacement.
Cochlear fluid movement, in turn, displaces the basilar membrane and
initiates traveling waves.

15. • Transmission routes for air conduction, right ear example
(narrow arrows) and bone conduction, right mastoid
example (bold arrows). Note: Higher intensity air-conducted
signals can activatethe bone conduction transmission route.

16. RINNES TEST
• In this test air conduction of the ear
is compared with its bone
conduction. A vibrating tuning fork is
placed on the patient’s mastoid and
when he stops hearing it is brought
beside the meatus. If he still hears,
AC is more than BC.
• Alternatively, the patient is asked to
compare the loudness of sound
heard through air and bone
conduction.
• Rinne test is called positive when AC
is longer or louder than BC. It is seen
in normal persons or those having
sensorineural deafness.
• A negative Rinne (BC > AC) is seen in
conductive deafness. A negative
Rinne indicates a minimum air-bone
gap of 15–20 dB.

17. • False Negative Rinne It is seen in severe unilateral sensorineural hearing
loss. Patient does not perceive any sound of tuning fork by air conduction
but responds to bone conduction testing.
• This response to bone conduction is, in reality, from the opposite ear
because of transcranial transmission of sound. In such cases, correct
diagnosis can be made by masking the non-test ear with Barany's noise
box while testing for bone conduction.

18. • A prediction of air-bone gap can be made if tuning forks of 256, 512 and
1024 Hz are used.
 Rinne test equal or negative for 256 Hz but positive for 512 Hz indicates
air-bone gap of 20-30 dB.
 Rinne test negative for 256 and 512 Hz but positive for 1024 Hz indicates
air-bone gap of 30-45 dB.
 Rinne negative for all three tuning forks, indicates air-bone gap of 45-60
dB .
Remember that a negative Rinne for 256, 512 and 1024 hz indicates a
minimum AB gap of 15, 30, 45 dB respectively

19. Rinnes Test
• Pts. with normal hearing and SNHL will hear the tone louder at the ear
(Because AC is a more efficient means of sound transmission to the IE than
BC) than behind the ear (Positive Rinne)
• Pts. with CHL (more than mild) or MHL will hear the tone louder with the
stem of the fork behind the ear because their BC hearing is better than
their AC hearing (Negative Rinne)

20. • The 256-Hz Rinne tuning fork test
will detect a conductive deafness
above 30 dB in 90 %of patients.
Between 20 and 30 dB, the
sensitivity will fall to 70 % and
between 10 and 20 dB will be less
than 50%
• The specificity of the test is high
above 30 db conductive deafness,
but falls as the air–bone gap
narrows.

21. Weber test
• In this test, bone conduction of
both the ars are compared with
one another
• A vibrating tuning fork is placed in
the middle of the forehead or the
vertex or chin or upper incisor
teeth and the patient is asked in
which ear the sound is heard.
• Normally, it is heard equally in
both ears.

22. • It is a very sensitive test and even a 5db difference in two ears is indicated
by this test
• The Weber tuning fork test is only applicable if a patient has asymmetrical
hearing as might be assesed by a preformed clinical test
• In conductive deafness the sound is lateralised to poor ear because
ambient noise does not disturb the diseased ear as much as the normal
ear

23. • Normally, it is heard equally in both ears. It is lateralized to the worse ear
in conductive deafness and to the better ear in sensorineural deafness.
• In weber test, sound travels directly to the cochlea via bone.
• Lateralization of sound in weber test with a tuning fork of 512 Hz implies a
conductive loss of 15–25 dB in ipsilateral ear or a sensorineural loss in the
contralateral ear.

25. Absolute bone conduction (ABC) test.
• Bone conduction is a measure of cochlear function.
• In ABC test, patient’s bone conduction is compared with that of the
examiner (presuming that the examiner has normal hearing).
• External auditory meatus of both the patient and examiner should be
occluded (by pressing the tragus inwards)to prevent ambient noise
entering through AC route. In conductive deafness, the patient and the
examiner hear the fork for the same duration of time. In sensorineural
deafness, the patient hears the fork for a shorter duration.

26. Schwabach’s test
• Here bone conduction of patient is compared with that of the normal
hearing person (examiner) but meatus is not occluded. It has the same
significance as absolute bone conduction test.
• Schwabach is reduced in sensorineural deafness and lengthened in
conductive deafness

27. Bing test
• It is a test of bone conduction and examines the effect of occlusion of ear
canal on the hearing. A vibrating tuning fork is placed on the mastoid
while the examiner alternately closes and opens the ear canal by pressing
on the tragus inwards.
• A normal person or one with sensorineural hearing loss hears louder when
ear canal is occluded and softer when the canal is open (Bing positive). A
patient with conductive hearing loss will appreciate no change (Bing
negative).

28. Gelle’s test
• It is also a test of bone conduction and examines the effect of increased
air pressure in ear canal on the hearing. Normally, when air pressure is
increased in the ear canal by Siegel’s speculum, it pushes the tympanic
membrane and ossicles inwards, raises the intralabyrinthine pressure and
causes immobility of basilar membrane and decreased hearing, but no
change in hearing is observed when ossicular chain is fixed or
disconnected.
• Gelle’s test is performed by placing a vibrating fork on the mastoid while
changes in air pressure in the ear canal are brought about by Siegel’s
speculum.
• Gelle’s test is positive in normal persons and in those with sensorineural
hearing loss. It is negative when ossicular chain is fixed or disconnected. It
was a popular test to find out stapes fixation in otosclerosis but has now
been superceded by tympanometry

29. Tuning fork tests &their interpretation
Test Normal Conductive
deafness
Sensorineural
deafness
Rinne AC>BC(RINNE
POSITIVE)
BC>AC AC>BC
Weber Not lateralized Lateralized to
poorer ear
Lateralized to
better ear
ABC Same as examiner’s Same as examiner’s Reduced
Schwabach Equal Lengthened Shortened

30. STENGER’S TEST
• This test is performed to identify feigned hearing loss and malingering.
• This test is based on the auditory phenomenon known as “Stenger’s
principle”. This principle states that when two similar sounds are
presented to both ears only the louder of the two would be heard.
Patients usually are not aware of this phenomenon.
• When two similar tuning forks of same frequencies are made to vibrate
and held simultaneously in the acoustic axis of both ears only the louder
fork will be heard. Loudness of vibrating fork can be adjusted by adjusting
the distance of the fork from the external canal. Usually the vibrating fork
is held closer to the allegedly deaf ear of the patient. The patient will not
acknowledge hearing in that ear. According to Stenger’s principle he
should be able to hear the louder fork. If the hearing loss in worse ear is
genuine, patient will respond to the signal presented to the better ear.
This is known as negative Stenger’s test. Feigning patient will not
acknowledge hearing when louder sound is presented to the worse ear.
This is known as positive Stenger’s test

31. CHIMANI-MOOS TEST
• This is actually a modification of Weber test. When the vibrating fork is
placed on the vertex, the patient indicates that he hears it in the good ear
and not in the deaf ear. The meatus of the good ear is then occluded.
• A genuine deaf patient will still be able to lateralize the sound to the good
ear, where as a malingerer will deny hearing the sound at all.

32. PURE TONE AUDIOMETRY:Definition
• MEASURING RELATIVE HEARING THRESHOLD USING PURE TONES IS
CALLED PURE TONE AUDIOMETRY.
• Hearing threshold is typically defined as the lowest (softest) sound level
needed for a person to detect a signal approximately 50% of the time
• The instrument used in the measurement of auditory threshold is known
as the audiometer.
• Patients hearing threshold is measured in comparison to ideal fixed
normal hearing level (0 dB) and thus is relative hearing threshold
measurement.
• PTA requires a subjective response from subject.

33. • Sound is generated when an object vibrates in elastic medium.
• No of sound waves set up in air by vibrating object in one second is known
as frequency measured in Hz.
• Object vibrating in single fixed frequency is called Sine wave.
• Sound sensation produced by this sine wave is called Pure tone.

34. WHY PURETONE THRESHOLDS?
• The auditory system is organized tonotopically(i.e., a frequency-to-
place mapping) from the cochlea to the cortex. The tonotopic organization
of the cochlea is a result of the frequency tuning of the basilar membrane
with high frequencies represented at the basal end and low frequencies at
the apical end. Damage to sensory cells of the cochlea at a specific place
along the basilar membrane can result in a loss of hearing that
corresponds to the frequencies coded by that place.
• For this reason, Pure tone threshold tests provide details that would
otherwise remain unknown if a broadband stimulus such as speech were
used.

35. CALIBERATION
• The human ear does not perceive
sound equally well at all frequencies.
The ear is most sensitive to sound in
the intermediate region from 1000 to
4000 Hz and is less sensitive at both
the higher and lower frequencies. In
normal ears more sound pressure is
needed to elicit a threshold response
at 250 Hz than at 2000 Hz.
• Hearing sensitivity is defined as the
threshold of audibility of pure-tone
signals, graphed in sound pressure
level (SPL) across a frequency range
that encompasses most of human
hearing. This curve representing
hearing sensitivity is often referred to
as the minimum audibility curve.

36. • The audiometer is calibrated to correct for these differences in threshold
sensitivity at various frequencies
• Consequently, when the hearing level dial is set at zero for a given
frequency, the signal is automatically presented at the normal threshold
sound pressure level required for the average young adult to hear that
particular frequency

37. Aims
• To find out any hearing loss or not.
• Degree of hearing dysfunction.
• Conductive or SNHL.
• If SNHL then cochlear or retrocochlear.
• To decide on the appropriate rehabilitation device which can be used to
minimise the hearing disability.

38. COMPONENTS OF A PURETONE AUDIOMETER
• Oscillator : The role of the oscillator in a Puretone audiometer is to generate
electronically standardized frequencies within +/- 3% of their nominal value. The
frequencies generated are 125,250, 500,750, 1000, 1500, 2000, 3000, 4000, 6000
and 8000 Hz.
• Interrupter switch : The tones presented to the patient should be switched on
and off. This feature is important because a continuous tone undergoes decay
during a period of time.
• Equalisation circuit : because the threshold of human hearing is not uniform
• Output power amplifier
• Hearing level attenuator: The attenuator can be varied in steps of 5 dB. The basic
reference point is marked as 'O'. This indicates -5 to -10 dB hearing threshold
levels.
• Outpur transducers: Is of three different types.
1. Ear phones
2. Bone vibrator
3. Loud speaker (free field audiometry(pediatric patients)

39. The basic design of a pure tone audiometer

40. Typical face of a pure-tone audiometer
• A) On-off power switch. (B) Output
selector switch. Selects right ear, left ear,
or bone conduction. Masking delivered to
nontest earphone for air conduction and
to left earphone for bone conduction. (C)
Frequency selector dial. Air conduction
and ,Bone conduction(D) Hearing-level
dial. Air-conduction range: –10 to 110 dB
HL (500 to 6000 Hz), –10 to 90 dB HL (250
and 8000 Hz), and –10 to 80 dB HL(125
Hz). Bone-conduction range: –10 to 50 dB
HL (250 Hz), –10 to 70 dB HL (500 Hz), and
–10 to 80 dB HL (750 to 4000 Hz). (E)
Tone-presentation bar. Introduces tone
with prescribed rise and fall time and no
audibles ound from the switch. (F)
Masking-level dial. Controls intensity of
masking noise in the nontest ear

41. • Proper positioning
during pure-tone
audiometry carried out
with a single sound-
treated room for (A)
examiner, (B)
audiometer, and (C)
patient

42. TECHNIQUE OF MEASUREMENT
• Some audiologists assess the threshold of air conduction by going from an
inaudible to an audible stimulus intensity. This method is known as
ascending method of estimation of threshold of hearing, while others
assess the threshold of air condution by going from an audible to an
inaudible stimulus intensity. This is known as descending method of
threshold estimation.

43. Symbols used in audiometry
• Blue line for left ear
• Red line for right ear
• Continuous line for air conduction
• Broken line for bone conduction

44. Instructions to the patient:
• The patient is instructed to raise the index finger if the sound
is heard. The patient should respond even if the sound is
faintly heard.
• Improper placement of head phones will cause threshold
variations of even 15 – 20 dB.
• Before placing the ear phones on the patient, the patient's
ear should be examined for the presence of wax.

45. Technique of recording air conduction threshold
• Most commonly used is Conventional Hughson & Westlake
technique (modified by carhart and jerger).

46. HUGHSON & WESTLAKE TECHNIQUE
• Complete history and examination
• Better ear tested first.
• 1000 Hz 2000 4000 8000 10,000 1000 500 250 Hz
• If difference between these octaves is >20dB then half octaves i.e.
750, 3000, 6000 Hz tested.
• Start with arbitrary supra threshold level. (Descending method)
• "Up 5-down 10" method of threshold estimation:
• The starting intensity of the test tone is reduced in 10 dB steps
following each positive response, until a hearing threshold level is
reached at which the subject fails to respond. Then, the tone is
raised by 5 dB, if the subject hears this increment, the tone is
reduced by 10 dB; if the tone is not heard then it is raised by
another 5 dB increment. This 5 dB increment is always used if the
preceding tone is not heard, and a 10 dB decrement is always used
when the sound is heard.

47. EXAMPLES OF DIAGNOSES
Normal-hearing Sensitivity
• Owing to calibration, air
conduction thresholds will be
near 0 dB HL,bone conduction
thresholds will be near 0 dB HL
and be similar to air conduction
thresholds (+_10DB).

48. • CHL with Air–Bone Gaps

49. • Sensorineural hearing loss. The
audiogram show no A-B gap.

50. • MHL with Air–Bone Gaps of Outer
or Middle Ear Origin

51. • Noise induced hearing loss.
• The audiogram in NIHL shows a
typical notch, at 4 kHz, both for
air and bone conduction (Figure ).
It is usually symmetrical on
bothsides.

52. • Ménière’s disease.
• Hearing loss is sensorineural and
more in lower frequencies—the
rising curve. As the disease
progresses, middle and higher
frequencies get involved and
audiogram becomes flat or falling
type (B & C)

53. • Otosclerosis
• Pure tone audiometry shows loss
of air conduction, more for lower
frequencies.
• Bone conduction is normal. In
some cases, there is a dip in bone
conduction curve.
• It is different at different
frequencies but maximum at
2000 Hz and is called Carhart’s
notch (5 dB at 500 Hz, 10 dB at
1000 Hz, 15 dB at 2000 Hz and 5
dB at 4000 Hz) (Figure ). Carhart’s
notch disappears after successful
stapedectomy

54. Uses of Pure Tone Audiogram
• It is a measure of threshold of hearing by air and bone conduction and
thus the degree and type of hearing loss.
• A record can be kept for future reference.
• Audiogram is essential for prescription of hearing aid.
• Helps to find degree of handicap for medicolegal purposes.
• Helps to predict speech reception threshold.

55. MASKING
• A major objective of the basic audiologic evaluation is assessment of
auditory function of each ear.
• Although a puretone or speech stimulus is being presented through a
transducer to the test ear, the nontest ear can contribute partially or
totally to the observed response.

56. • Whenever it is suspected that the nontest ear is responsive during
evaluation of the test ear, a masking stimulus must be applied to the
nontest ear to eliminate its participation

57. • Cross hearing occurs when a stimulus presented to the test ear “crosses
over” and is perceived in the nontest ear. There are two parallel pathways
by which sound presented through an earphone (i.e., an air-conduction
transducer) can reach the nontest ear. Specifically, there are both bone-
conduction and air-conduction pathways between an air-conduction signal
presented at the test ear and the sound reaching the nontest ear cochlea.
• Cross hearing is the result of limited interaural attenuation(IA).

58. • IA refers to the “reduction of energy between ears.” Generally, it
represents the amount of separation or the degree of isolation between
ears during testing. Specifically, it is the decibel difference between the
hearing level (HL) of the signal at the test ear and the HL reaching the
nontest ear:
IA = dBHLTestEar – dBHLNontestEar

59. • Interaural attenuation (IA) is
calculated as the difference
between the hearing level (HL) of
the signal at the test ear and the
HL reaching the nontest ear
cochlea. A puretone signal of 90
dB HL is being presented to the
test ear through traditional supra-
aural earphones.
• Example A: If IA is 40 dB, then 50
dB HL is reaching the nontest ear
cochlea.
• Example B: If IA is 80 dB, then 10
dB HL is reaching the nontest ear
cochlea

60. • Expected unmasked puretone air-
and bone-conduction thresholds
in an individual with normal
hearing in the left ear and a
profound sensory/neural hearing
loss in the right ear. Without the
use of appropriate contralateral
masking, a shadow curve will
result in the right ear.
• Unmasked air-conduction
thresholds in the right ear will
shadow the bone-conduction
thresholds in the better (i.e., left)
ear by the amount of interaural
attenuation.

61. IMPEDANCE AUDIOMETRY
It is an objective test, widely used in clinical practice and is particularly useful
in children. It consists of:
• (a) Tympanometry
• (b) Acoustic reflex measurements
(a) Tympanometry. It is based on a simple principle, i.e.when a sound strikes
tympanic membrane, some of the sound energy is absorbed while the rest
is reflected. A stiffer tympanic membrane would reflect more of sound
energy than a compliant one. By changing the pressures in a sealed
external auditory canal and then measuring the reflected sound energy, it
is possible to find the compliance or stiffness of the tympano-ossicular
system and thus find the healthy or diseased status of the middle ear.

62. • The equipment consists of a probe which snugly fits into the external
auditory canal and has three channels:
• (i) to deliver a tone of 220 Hz,
• (ii) to pick up the reflected sound through a microphone and
• (iii) to bring about changes in air pressure in the ear canal from positive to
normal and then negative .
By charting the compliance of tympano-ossicular system against various
pressure changes, different types of graphs called tympanograms are
obtained which are diagnostic of certain middle ear pathologies.

63. • Type A: Normal tympanogram.
1. Type As: Compliance is lower at or near ambient air pressure. Seen in
fixation of ossicles, e.g. otosclerosis or malleus fixation.
2. Type Ad: High compliance at or near ambient pressure. Seen in ossicular
discontinuity or thin and lax tympanic membrane.
• Type B :A flat or dome-shaped graph. No change in compliance with
pressure changes. Otitis media with effusion, space-occupying lesions of
the tympanic cavity, and tympanic membrane perforations
• Type C: Maximum compliance occurs with negative pressure in excess of
100 mm H2O. Seen in retracted tympanic membrane and may show some
fluid in middle ear.
• Type D curve: which shows a notch in the pressure peak, is often seen
with scarred eardrums or with normal, hypermobile eardrums.

65. • (B)Acoustic reflex. It is based on the fact that a loud sound, 70–100 dB
above the threshold of hearing of a particular ear, causes bilateral
contraction of the stapedial muscles which can be detected by
tympanometry. Tone can be delivered to one ear and the reflex picked
from the same or the contralateral ear.

67. CLINICAL USES
To test the hearing in infants and young children.
To find malingerers. A person who feigns total deafness and does not give any
response on pure tone audiometry but shows a positive stapedial reflex is a
malingerer.
To detect cochlear pathology. Presence of stapedial reflex at lower intensities, e.g. 40–
60 dB than the usual 70 dB indicates recruitment and thus a cochlear type of
hearing loss
To detect VIIIth nerve lesion. If a sustained tone of 500 or 1000 Hz, delivered 10 dB
above acoustic reflex threshold, for a period of 10 s, brings the reflex amplitude
to 50%, it shows abnormal adaptation and is indicative of VIIIth nerve lesion
(stapedial reflex decay).
Lesions of facial nerve. Absence of stapedial reflex when hearing is normal indicates
lesion of the facial nerve, proximal to the nerve to stapedius. The reflex can also
be used to find prognosis of facial paralysis as the appearance of reflex, after it
was absent, indicates return of function and a favourable prognosis.
Lesion of brainstem. If ipsilateral reflex is present but the contralateral reflex is
absent, lesion is in the area of crossed pathways in the brainstem.

68. REFERENCES
• HANDBOOK OF CLINICAL AUDIOLOGY, 7th edition, JACK KATZ.
• Cummings Otolaryngology HEAD AND NECK SURGERY
• Clinical Audiology An Introduction SECOND EDITION, Brad A. Stach
• Scott brown 7th edition.

69. •Thank
you