2. Objectives:
1. Define deafness
2. Differentiate conductive from perceptive deafness and
enumerate their causes
3. Perform tunning fork hearing tests to test hearing.
4. Describe how to use hearing test to differentiate between the
two types .
Reference for further study:Pflanzer: Experimental and Applied Physiology Laboratory Manual,
7 th edition 2003 chapter 14, Hearing and Equilibrium, 171 – 186.
3. Hearing loss:
A person who is not able to hear as well as someone with
normal hearing – hearing thresholds of 25 dB or better in both
ears – is said to have hearing loss.
Mild, Moderate, Severe, or Profound.
Can affect one ear or both ears, and leads to difficulty in
hearing conversational speech or loud sounds.
4. Define:Deafness
★ Deaf people mostly have profound hearing loss, which
implies very little or no hearing.
★ They often use sign language for communication.
WHO defined Deafness as “a hearing impairment that is so
severe that the child is impaired in processing linguistic
information through hearing, with or without amplification.”
5.
6. 1:Conductive deafness
★ Impaired sound transmission in the external or middle ear
★ Impacts all sound frequencies.
★ Impairment of the physical structures of the ear that conduct
sound itself to the cochlea.
Causes:
➔ Plugging of external auditory canals by wax or foreign bodies
➔ Otitis media
➔ Osteosclerosis
➔ Tympanumossicular system has been destroyed or ankylosed
(“frozen” in place by fibrosis or calcification).
7. 2: Sensorineural deafness
★ Impairment of the cochlea, cochlear hair cells loss, the auditory
nerve, or the central nervous system circuits from the ear.
★ Impairs the ability to hear certain pitches while others are
unaffected.
8. Causes of sensorineural deafness
➔ Prolonged exposure to noise
➔ Craniofacial anomalies
➔ Down syndrome,
➔ Rubella ,Drugs or alcohol consumption (during pregnancy )
➔ low birth weight (<1.6 kg)
➔ Incubator noise affecting premature infants
➔ Neonatal exposure to aminoglycosides or ototoxic drugs
➔ Bacterial infections (meningitis)
➔ Cytomegalovirus ,Toxoplasmosis ,herpes,syphilis, or flu
➔ Accidents involving head injuries.
9. Auditory Function Tests
I:Noise maker test
1) Whisper test
2) Watch-Tick Test
3) Calling Name Test
4) Ball Pen-Click Test
5) Command Test
II:Tuning fork test: Conduction
A. Weber test
B. Rinne test
C. Schwabach test
11. Tunning fork for hearing test
Weber test:256 Hz
Rinne Test:512 Hz
12. weber Rinne Schwabach
Method Base of vibrating tunning
fork placed on vertex of
head
Base of vibrating tuning
fork placed on mastoid
until subject no longer
hears it , then held in air
next to ear
Bone conduction of
patient compared with
that of normal subject
Normal Hears equally on both
sides
Hears vibration in air after
bone conduction is over
Conduction
deafness
(one Ear)
Sound louder in diseased
ear as masking effect of
environmental noise is
absent on diseased side
Vibration in air not heard
after bone conduction is
over
Bone conduction
better than normal
Sensorineural
deafness
(one ear)
Sound louder in normal
ear
Vibration heard in air after
bone conduction is over,
ias long as nerve deafness
is partial
Bone conduction
worse than normal.
13. Weber test
Quick screening test for hearing.
Strike the tuning fork 256-Hz prong firmly against the
heel of your palm to start it vibrating.
Place the tip of the handle in the median line of the skull
or forehead of the subject or vertex.
Perform the test again, asking the subject to block
one external auditory canal with a finger before repeating the test.
The sound should be louder on the blocked side.
Repeat the test blocking the other ear.
Record your observations in the report.
14. Inference
★ If hearing is normal, the subject will hear the sound equally in both
ears.
The sound should be louder on the blocked side.
★ Similar effects occur in conduction impairments of hearing because
the conductive loss masks some of the environmental noise, thus
making the cochlea more efficient on the diseased (or blocked) side.
★ In sensorineural impairments, Weber test results in the sound’s
being louder in the unaffected ear.
15. Rinne test:
Comparison of the duration of air conduction(AC) with that of bone conduction(BC).
Procedure:
Strike the prong of a 512 Hz tuning fork firmly against the heel of your palm to start
it vibrating.
Place the tip of the tuning fork handle on the mastoid process
with the prongs directed toward back of head.
Take care not to touch the prongs of the fork against the ear or hand.
As soon as the subject no longer hears the sound,
move the tuning fork to within 1 inch of thee
external auditory meatus, & the subject should again be able to hear the sound.
Repeat the test for other ear.
16. Inference:
★ Rinne test is designated as positive(Normal) : suggests no conductive
hearing loss.AC>BC
Normally the sound conducted by air transmission is heard several seconds
longer than that conducted by bone transmission because the threshold for
air transmission is lower.
★ Rinne test is designated as negative ( conductive hearing loss).
AC = or < BC
★ False negative:BC>AC sound is heard due to transcranial transmission
from opposite good ear .Seen mostly in unilateral perceptive deafness.
