Selection of Tuning fork: Tuning forks of varying frequencies such as 128, 256, 512, 1024, 2048 and 4096 hertz are available in the market. In clinical practice, tuning fork of 512 Hz is considered ideal (Optimum decay time and produce minimal overtones). Shorter frequency forks are not preferred as they give a sense of bone vibration, while higher frequency forks are not preferred due to their shorter decay time. Tuning fork tests Tuning fork tests Tuning fork tests Tuning fork tests
Setting tunic fork into vibration :
- Hold tunic fork from its stem.
- To activate tuning fork, strike it gently against the examiner’s elbow, the heel of the hand or the rubber heel of the shoe.
- To produce a pure tone, strike the prong at a point 1/3rd of its length from its free end (this will minimize overtones and produce accurate results.)
Pre-requisites for tuning fork tests:
- Explain to the patient that he should raise his finger when he no longer hears the sound.
- The practitioner stabilizes the patient’s head with one hand.
To test air conduction (AC), a vibrating fork is placed vertically in line with the meatus, about 2 cm away from the opening of the external auditory canal. The sound waves are transmitted through the tympanic membrane, middle ear and ossicles to the inner ear. Thus, by the air conduction test, the function of both the conducting mechanism and the cochlea are tested. Normally, hearing through air conduction is louder and heard twice as long as through the bone conduction route.
To test bone conduction (BC), the footplate of the vibrating tuning fork is placed firmly on the mastoid bone. The cochlea is stimulated directly by vibrations conducted through the skull bones. Thus, BC is a measure of the cochlear function only.
The clinically useful tuning fork tests include:
- Rinne’s test. The base of a vibrating tuning fork is kept on the mastoid bone of the patient. When the subject indicates that he can’t hear the sound anymore, the tuning fork is brought 25 mm (2.5 cm) in front of external auditory canal, parallel to the acoustic axis. If he still hears the sound, it means air conduction is more than bone conduction. Alternatively, the patient may be asked to compare the loudness of sound heard through air and bone conduction.
Interpretation of Rinne’s test:
- Rinne’s positive. AC > BC. It is seen in normal persons or patients having sensorineural deafness.
- Rinne’s negative. BC > AC. It is seen in patients having conductive deafness.
- Rinne’s false negative is seen in severe unilateral sensorineural hearing loss. The patient is able to perceive the sound of vibrating tuning fork when placed on mastoid but not in front of the ear. This response is a transcranial transmission of sound to the contralateral healthy ear. To differentiate it from ‘true negative’, the non-test ear is masked with Barany’s noise box while testing for bone conduction. Also, confirmation can be aided by the Weber test which it is lateralized to the better ear.
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 an air-bone gap of 20–30 dB.
- A Rinne test negative for 256 and 512 Hz but positive for 1024 Hz indicates an air-bone gap of 30–45 dB.
- A Rinne negative for all the three tuning forks of 256, 512 and 1024 Hz indicates an 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.
2. Weber’s test in conjunction with Rinne’s test helps the clinical diagnosis, especially in unilateral hearing loss. Procedure: Place the vibrating tuning fork in the middle of the forehead/ vertex/ central incisors/ mandibular symphysis from where it will be conducted directly to the cochlea. Ask the patient in which ear, hearing is better.
Interpretation of weber’s test:
- Normally, it is heard equally in both ears.
- Lateralisation: It is lateralised to the worse ear in conductive deafness (this is due to loss of ambient noise or failure to dissipate sound because of the ossicular discontinuity). It is lateralised to the better ear in sensorineural deafness (as sound travels directly to the cochlea via bone).
3. Absolute Bone Conduction test. In this test, the bone conduction of the patient is compared with that of the examiner presuming that the examiner’s hearing status is normal. Procedure: The patient’s external auditory canal is blocked by the examiner by pressing over the tragus. Now place the vibrating tuning fork on the mastoid bone. When the patient indicates that he no longer hears the sound, the same tuning fork is placed on the mastoid bone of the examiner with ear occlusion same as done in the patient.
Interpretation of absolute bone conduction test:
- Normal subjects & Conductive deafness – The examiner does not perceive the sound which implies, both the patient and the examiner hear the sound for same time.
- Sensorineural deafness – The examiner is still able to hear the sound which implies, the patient was able to perceive the sound for a lesser duration.
4. Schwabach test. Bone conduction of the patient is compared with that of the normal hearing person (examiner) but in this test, the meatus is not occluded.
Interpretation of schwabach test: Same as absolute bone conduction test.
5. Bing Test: Place a vibrating tuning fork on the patient’s mastoid process. Alter the air pressure in the ear canal by closing/ opening the ear canal by alternatively pressing on the tragus. Ask the patient whether there is any increase or decrease in the sound of the vibrating tuning fork.
Interpretation of bing test:
- Normal or Sensorineural hearing loss – Patient hears louder when the ear canal is blocked and softer when the canal is not blocked (Bing positive).
- Conductive hearing loss – No such change in hearing is seen in patients with fixed or disconnected ossicular chain (Bing negative).
6. Gelle’s test. It is an excellent test for determining the functional status of the ossicular chain. Procedure: Place a vibrating tuning fork on the patient’s mastoid process. Alter the air pressure in the ear canal using a Siegel’s speculum. Ask the patient whether there is any increase or decrease in the sound of the vibrating tuning fork.
Interpretation of Gelle’s test:
- In normal subjects, raised air pressure in the ear canal by Siegel’s speculum will push the tympanic membrane and ossicles inwards. This will raise the intralabyrinthine pressure leading to immobility of the basilar membrane and thus reduced hearing.
- However, no such change in hearing is seen in patients with fixed or disconnected ossicular chain (conductive hearing loss).
TUNING FORK TESTS AND THEIR INTERPRETATION
|Test||Normal||Conductive deafness||SN deafness|
|Rinne||AC > BC (Rinne positive)||BC > AC (Rinne negative)||AC>BC|
|Weber||Not lateralized||Lateralized to poorer ear||Lateralized to better ear|
|ABC||Same as examiner’s||Same as examiner’s||Reduced|
——— End of the chapter ———
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Dr. Rahul Kumar Bagla
MS & Fellow Rhinoplasty & Facial Plastic Surgery.
Associate Professor & Head
GIMS, Greater Noida, India