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Tuning Fork Tests

TUNING FORK TESTS

Selection of Tuning fork: The selection of an appropriate tuning fork is crucial, with frequencies such as 128, 256, 512, 1024, 2048 and 4096 hertz available. In clinical practice, a tuning fork of 512 Hz is preferred due to its optimal decay time and minimal overtones, making it ideal for accurate testing. Lower frequency forks tend to produce sense of bone vibrations, while higher frequencies have shorter decay times, which can affect test results.

Setting tunic fork into vibration : To initiate the test, the practitioner should hold the tuning fork by its stem and strike it gently against a stable surface, such as the examiner’s elbow or the heel of their hand. For optimal results, it is recommended to strike the prong approximately one-third of its length from the free end to minimize overtones and produce a pure tone.

Pre-requisites for tuning fork tests: Before conducting the tests, it is essential to explain the procedure to the patient, instructing them to raise a finger when they can no longer hear the sound. Additionally, the practitioner should stabilize the patient’s head to ensure accurate results.

Testing Methods. The tuning fork tests primarily assess two types of conduction: air conduction (AC) and bone conduction (BC).

  • Air Conduction (AC) Test: The vibrating tuning fork is placed vertically about 2 cm from the external auditory canal. Sound waves travel through the tympanic membrane, middle ear, and ossicles to the inner ear, allowing evaluation of both the conducting mechanism and cochlear function. Typically, sound heard through air conduction is louder and lasts longer than through bone conduction.
  • Bone Conduction (BC) Test: The footplate of the vibrating tuning fork is placed on the mastoid bone. This method stimulates the cochlea directly through vibrations transmitted via the skull bones, measuring cochlear function alone.

Assessment of hearing - Hearing tests

The clinically useful tuning fork tests include:

  1. Rinne’s Test: In this test, the base of the vibrating tuning fork is placed on the mastoid bone. When the patient can no longer hear the sound, the fork is moved 2.5 cm in front of the external auditory canal. If the patient hears the sound again, it indicates that air conduction is superior to bone conduction.
    • Interpretation:
      • Positive Rinne: AC > BC, indicating normal hearing or sensorineural deafness.
      • Negative Rinne: BC > AC, indicating conductive deafness.
      • False Negative: In cases of severe unilateral sensorineural hearing loss, the patient may hear the sound on the mastoid but not in front of the ear. This can be confirmed with masking techniques and the Weber test.

The degree of air-bone gap can be assessed using tuning forks of 256, 512, and 1024 Hz, with specific interpretations for each frequency.

    • 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: This test involves placing the vibrating tuning fork in the middle of the forehead / vertex/ central incisors or mandibular symphysis from where it will be conducted directly to the cochlea. The patient is asked to identify which ear hears the sound better.

    • Interpretation:
      • Normal hearing results in equal sound perception in both ears.
      • In conductive hearing loss, sound lateralizes to the affected ear (this is due to loss of ambient noise or failure to dissipate sound because of the ossicular discontinuity), while in sensorineural loss, it lateralizes to the unaffected ear (as sound travels directly to the cochlea via bone).

    3. Absolute Bone Conduction Test: This test compares the bone conduction of the patient to that of the examiner, assuming the examiner has normal hearing. With the patient’s ear occluded by the examiner by pressing over the tragus, the tuning fork is placed on the mastoid bone.

      • Interpretation:
        • Normal or conductive deafness: Both the patient and examiner hear the sound for the same duration.
        • Sensorineural deafness: The examiner continues to hear the sound longer than the patient.

    4. Schwabach Test: Similar to the absolute bone conduction test, but without occluding the ear canal.

    5. Bing Test: The tuning fork is placed on the mastoid process while altering air pressure in the ear canal by closing/ opening the ear canal by alternatively pressing on the tragus.

      • Interpretation:
        • Normal or sensorineural hearing loss: Sound increases when the ear canal is blocked (Bing positive). 
        • Conductive hearing loss: No change in sound perception occurs in patients with fixed or disconnected ossicular chain (Bing negative).

    6. Gelle’s Test: This test assesses the functional status of the ossicular chain by altering air pressure in the ear canal while the tuning fork is placed on the mastoid process.

      • Interpretation:
        • Normal subjects experience a decrease in sound perception with increased air pressure, while patients with conductive hearing loss show no change.

    Tuning fork tests remain a valuable tool in clinical practice for evaluating hearing loss, providing quick and effective assessments that can guide further audiometric testing when necessary.

     

    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
    Schwabach Equal Lengthened Shortened

     

    ——— End of the chapter ———

    Learning resources.

    • Scott-Brown, Textbook of Otorhinolaryngology Head and Neck Surgery.
    • Glasscock-Shambaugh, Textbook of  Surgery of the Ear.
    • P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
    • Hazarika P, Textbook of Ear Nose Throat And Head Neck Surgery Clinical Practical.
    • Mohan Bansal, Textbook of Diseases of Ear, Nose and Throat Head and Neck surgery.
    • Anirban Biswas, Textbook of Clinical Audio-vestibulometry.

      Author:

    Dr. Rahul Bagla ENT Textbook

    Dr. Rahul Bagla
    MBBS (MAMC, Delhi) MS ENT (UCMS, Delhi)
    Fellow Rhinoplasty & Facial Plastic Surgery.
    Renowned Teaching Faculty
    Mail: msrahulbagla@gmail.com
    India