Monday, December 27, 2010

Tuning Fork Tests: Rinne, Weber, ABC, Schwabach’s Test

The clinically useful tuning fork tests include:
(a) Rinne 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 Be. Alternatively, the patient is
asked co compare the loudness of sound heard through
air and bone conduction. Rinne test is called positive
when AC is longer or louder than Be. 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.
A prediction of air-bone gap can be made if tuning
forks of 256, 512 and 1024 Hz are used.
• A Rinne test equal or negative for 256 Hz but positive
for 512 Hz indicates air-bone gap of 20-30 dB.
• A Rinne test negative for 256 and 512 Hz but
positive for 1024 Hz indicates air-bone gap of
30-45 dB.
• A Rinne negative for all the three tuning forks of
256, 512 and 1024 Hz, 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
respecti vel y.
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. Weber test will
further help as it gets lateralised to the better ear.
(b) Weber test. In this test, a Vibrating tuning fork
is placed in the middle of the forehead or the vertex and
the patient is asked in which ear the sound is heard.
Normally, it is heard equally in both ears. It is lateralised
to the worse ear in conducti ve deafness and to the better
ear in sensorineural deafness. In weber test, sound travels
directly to the cochlea via bone. Lateralisation 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.
(c) 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.
(d) Schwabach's test. Here again BC 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.

3 comments:

  1. False negative Rinne. It is seen in severe unilateral sensorineural
    hearing loss gladys

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