HEARING ASSESSMENT BY TUNING FORK: QUESTIONS AND ANSWERS
Q. WHO INVENTED THE TUNING FORK?
John Shore in 1711.
Q. WHAT ARE THE DIFFERENT DISTANCES AT WHICH THE FOLLOWING SOUND IS HEARD?
Whisper: 12 feet
Conversational voice: 20-40 feet
Q. HOW IS WHISPER TEST DONE?
Whisper is given with the residual air after full expiration.
The results are interpreted as follows:
Whisper voice heard at 2 feet: Normal hearing
Conversation heard at 2 feet: 30-70 dB
Loud conversation heard at 2 feet: >70 dB
Q. WHAT DOES AIR CONDUCTION TEST INDICATE? WHAT ARE THE MEASURE WE TAKE WHILE PERFORMING AIR CONDUCTION TEST BY TUNING FORK?
Air conduction test indicates the integrity of tympano-ossicular chain. Thus AC is also called ossicular conduction.
The following are different measures to be taken while doing air conduction by tuning fork:
Place the tuning fork parallel to EAC.
The tuning fork must be in the distance of 1/2 to 1 inch from EAC opening.
Hold tuning fork firmly by the stem.
Do not strike on the hard surfaces as it produces overtone.
Q. WHAT DOES BONE CONDUCTION SIGNIFY?
BC signifies the sound conduction through the cochlea, auditory nerve and it’s central connections. Hence, provides an information about the integrity of the inner ear function.
Sound through BC is transmitted by the vibration of the skull bone. Two types of vibrations occur:
INERTIA TYPE (For frequency below 800): It occurs when the skull vibrates as one unit and the ossicles, mandible and cochlear fluid lags behind due to inertia.
COMPRESSION TYPE (For frequency above 800): Vibration acts on the fluids of inner ear and its movements.
Q. WHICH IS MORE SENSITIVE: RINNE OR WEBER TEST?
Weber test is more sensitive than Rinne test because it can detect hearing differences between two ears even if the hearing loss is < 5 dB as the lateralization.
Q. WHY IS WEBER LATERALIZED TO DISEASED EAR IN CHL?
The sound is lateralized to the diseased ear in the CHL because the ambient noise does not disturb the diseased ear as much as the normal ear. Thus the sound is more prominent in the diseased ear compared to normal ear which can have proper sound conduction from the surrounding.
Q. WHEN IS RINNE TEST NEGATIVE? HOW WILL YOU INTERPRET IT?
Rinne test will be negative in conductive deafness of more than 15 dB to 20 dB.
Interpretation is done as follows:
NORMAL (RINNE +VE)
CONDUCTIVE HEARING LOSS (RINNE -VE)
SENSORY HEARING LOSS ( LOW +VE RINNE)
AC>BC but the duration is reduced
SEVERE UNILATERAL SNHL (FALSE -VE)
BC>AC (This is due to transcranial transmission of sounds to normal ear when the tuning fork is placed on the mastoid)
MILD CONDUCTIVE DEAFNESS (RINNE EQUIVOCAL)
When Rinne is negative with 256 HZ but positive with 512 Hz : AB gap of 20-30 dB.
When Rinne is negative with 512 Hz but positive with 10,24 Hz: 30 to 45 dB.
Q. WHAT ARE THE VARIOUS TUNING FORK TESTS?
-BC compared between patient and examiner without meatal occlusion
-Shortened in SNHL
-Lengthened in CHL
Absolute Bone Conduction test:
-Similarly performed like Schwabach’s test but with occlusion of meatus.
-If the patient hears for the same duration as an examiner : Normal or CHL
-If the patient hears for the less duration than an examiner : SNHL
-Test BC with seigle’s speculum in EAC.
-If the hearing decreases on increasing of pressure: Normal or SNHL.
-If the hearing not affected on by change of pressure: Gelle’s negative → Ossicular discontinuity / Otosclerosis
– BC is tested with alternating closing and opening of EAC.
-On occlusion, if the sound is increased (BING +VE): Normal or SNHL.
-On occlusion, if there is no change in sound (BING -VE): CHL
Other tuning fork tests used specially for malingering cases are: