Hearing Assessment Techniques

Tuning Forks & PTA Basics - Striking a Chord

• Tuning Forks: Frequencies: 256 Hz, 512 Hz, 1024 Hz.
  • Rinne Test: AC vs BC.
    • Normal/SNHL: AC > BC (+ve).
    • CHL: BC > AC (-ve). 📌 Rinne Negative in CHL.
  • Weber Test: Midline fork lateralization.
    • CHL: To poorer ear. 📌 Weber to Bad ear in CHL.
    • SNHL: To better ear.
  • Schwabach Test: Patient BC vs Examiner BC. Shortened in SNHL.
  • Absolute Bone Conduction (ABC): Patient BC vs Examiner BC (tragus occluded). Reduced in SNHL.
• Pure Tone Audiometry (PTA):
  • Measures hearing thresholds (dBHL) for tones (125Hz-8000Hz).
    • AC & BC plotted on audiogram. 0 dBHL = normal young adult avg.
  • Air-Bone Gap (ABG): AC - BC >10 dB.
    • Indicates CHL.
  • Hearing Loss Types (Audiogram):
    • CHL: ↓AC, Normal BC, ABG present.
    • SNHL: ↓AC & ↓BC (similar), No ABG.
    • Mixed: ↓AC & ↓BC, ABG present.

⭐ The 512 Hz tuning fork is preferred for clinical testing as it balances audibility and tactile sensation.

Audiogram Analysis & Speech Audiometry - Deciphering Decibels

• Audiogram Interpretation:

  • Degree of Hearing Loss (PTA: 0.5, 1, 2, 4 kHz avg.):
    • Normal: ≤ 25 dB HL
    • Mild: 26-40 dB HL
    • Moderate: 41-55 dB HL
    • Moderately Severe: 56-70 dB HL
    • Severe: 71-90 dB HL
    • Profound: > 90 dB HL
  • Configuration: Sloping (presbycusis), rising, flat, U-shaped (cookie-bite), notch (e.g., 4 kHz NIHL).
  • Type: See flowchart below (based on AC, BC, Air-Bone Gap).

    ⭐ A significant Air-Bone Gap (>15 dB) on an audiogram is characteristic of conductive hearing loss.

• Speech Audiometry:

  • Speech Reception Threshold (SRT): Lowest level spondees identified 50%. Agrees with PTA ±10 dB.
  • Speech Discrimination Score (SDS)/Word Recognition Score (WRS): % PB words correct at 30-40 dB SL (re: SRT).
    • Assesses clarity; differentiates cochlear vs. retrocochlear.
    • Roll-over: ↓ WRS at ↑ intensity (retrocochlear sign).
  • Speech Detection Threshold (SDT)/Speech Awareness Threshold (SAT): Lowest level speech detected.

Objective Hearing Tests - Unbiased Ears

• Tympanometry: Middle ear assessment. Normal pressure: +50 to -100 daPa.
  • Jerger's Types: A (Normal), As (Stiff; Otosclerosis), Ad (Flaccid; Ossicular Discontinuity), B (Flat; OME/TM Perf.), C (< -100 daPa; ETD).
• Acoustic Reflex (AR): Stapedial reflex to loud sound (70-100 dB HL > threshold).
  • Absent/↑ in CHL, SNHL > 50-60 dB, retrocochlear lesions. Reflex Decay: Retrocochlear sign.
• Otoacoustic Emissions (OAEs): Cochlear Outer Hair Cell (OHC) sounds (TEOAEs, DPOAEs).
  • Screening: Present if hearing better than 30-40 dB HL.

  ⭐ Otoacoustic emissions (OAEs) are absent in individuals with sensorineural hearing loss worse than 30-40 dB HL, making them an excellent screening tool for cochlear function.

• Auditory Brainstem Response (ABR/BERA): Auditory nerve & brainstem electrical response.
  • Waves I-V Sources: I (CN VIII - Electrical Cochlear Output), II (Cochlear Nuc.), III (Sup. Olivary), IV (Lateral Lemniscus), V (Inferior Colliculus). 📌 Mnemonic: ECOLIMA (for waves I-V).
  • Uses: Hearing threshold estimation (esp. infants), retrocochlear diagnosis (↑ I-V IPL).
• Newborn Hearing Screening (NHS):

High‑Yield Points - ⚡ Biggest Takeaways

• Rinne (AC vs BC) & Weber (lateralization) differentiate Conductive Hearing Loss (CHL) from Sensorineural Hearing Loss (SNHL).
• Pure Tone Audiometry (PTA) is the gold standard for hearing thresholds; an air-bone gap signifies CHL.
• Tympanometry assesses middle ear function & compliance (Types A, As, Ad, B, C).
• Otoacoustic Emissions (OAEs) screen cochlear (outer hair cell) function, vital in newborn hearing screening.
• Auditory Brainstem Response (ABR/BERA) evaluates auditory pathway integrity to the brainstem; detects retrocochlear lesions.
• Speech Audiometry measures Speech Reception Threshold (SRT) (softest speech understood) & Speech Discrimination Score (SDS) (clarity).