Tuning Fork Tests ent

Tuning Fork Tests

Instrument: Tests performed with forks of varying frequencies (128, 256, 512, 1024, 2048, 4096 Hz).

  • Ideal Frequency: 512 Hz (Routine clinical practice).
  • Why?
    • Lower frequencies (e.g., 128 Hz) produce a sense of bone vibration.
    • Higher frequencies have a shorter decay time.
  • Activation: Strike gently against examiner’s elbow, heel of hand, or rubber heel of shoe.

Mechanism of Hearing Routes

  • Air Conduction (AC): Fork placed 2 cm from meatus. Waves travel via Tympanic Membrane → Middle Ear → Inner Ear. Tests Conducting mechanism + Cochlea.
  • Bone Conduction (BC): Footplate on mastoid. Vibrations stimulate cochlea directly through skull. Tests Cochlear function only.
  • Normal Physiology: AC is louder and heard twice as long as BC.

Clinical Tests

1. Rinne Test

Principle: Compares Air Conduction (AC) vs. Bone Conduction (BC).

Procedure: Fork on mastoid → when sound stops, move to meatus. (Or ask patient to compare loudness).

Rinne test Rinne test
Result Interpretation Condition
Positive AC > BC Normal or Sensorineural Hearing Loss (SNHL).
Negative BC > AC Conductive Deafness (Min. Air-Bone Gap 15-20 dB).
Prediction of Air-Bone (AB) Gap (Negative Rinne):
  • Negative for 256 Hz (Positive for 512): Gap 20–30 dB.
  • Negative for 256 & 512 Hz (Positive for 1024): Gap 30–45 dB.
  • Negative for 256, 512 & 1024 Hz: Gap 45–60 dB.

Rule of Thumb: Negative Rinne for 256, 512, 1024 Hz implies min AB gap of 15, 30, 45 dB respectively.

False Negative Rinne:
Seen in severe Unilateral SNHL (Dead ear). Patient responds to BC, but the sound is actually heard by the opposite (healthy) ear via transcranial transmission.
Confirmation: Mask non-test ear with Barany’s noise box. Weber test lateralizes to better ear.

2. Weber Test

Procedure: Fork placed on middle of forehead or vertex.

Weber test Weber test
Lateralization?
  • Midline: Normal or Equal hearing loss.
  • Lateralized to WORSE ear: Conductive Deafness.
  • Lateralized to BETTER ear: Sensorineural Deafness.

Note: Lateralization with 512 Hz implies Conductive loss of 15–25 dB (ipsilateral) or SNHL (contralateral).

3. Absolute Bone Conduction (ABC) Test

Principle: Compare Patient's BC vs. Examiner's BC (assumed normal).

Technique: Meatus Occluded (Tragus pressed inwards) to exclude ambient AC noise.

  • Same duration: Normal or Conductive Deafness.
  • Reduced duration: Sensorineural Deafness.

4. Schwabach’s Test

Same as ABC but Meatus is NOT Occluded.

  • Lengthened: Conductive Deafness.
  • Shortened: Sensorineural Deafness.

5. Bing Test (Effect of Occlusion)

Fork on mastoid. Examiner alternately opens/closes ear canal.

  • Positive (Change perceived): Louder when occluded. (Normal or SNHL).
  • Negative (No change): Conductive Hearing Loss.

6. Gelle’s Test (Effect of Pressure)

Fork on mastoid + Air pressure increased in canal using Siegel’s speculum.

  • Positive (Hearing Decreased): Normal or SNHL. (Increased pressure pushes ossicles → immobilizes basilar membrane).
  • Negative (No Change): Fixed Ossicular Chain (e.g., Otosclerosis) or Disconnected chain.

Summary: Interpretation Table

Test Normal Conductive Deafness SNHL
Rinne Positive (AC > BC) Negative (BC > AC) Positive (AC > BC)
Weber Not lateralized Lateralized to Poorer ear Lateralized to Better ear
ABC Same as Examiner Same as Examiner Reduced
Schwabach Equal Lengthened Shortened
📚 Source: Dhingra ENT | Chapter 4

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