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Test For Cochlear & Retrocochlear


Hearing loss


Retro cochlear







Tone decay test

Carhart’s method

Acoustic reflex decay test

Beksey audiometry


Speech Test

  1. Tone decay test:
    Is the measure of the rapidity of deterioration in the threshold of hearing when a continuous sustained sound is presented to the ear.
    1. Carhart’s Method
      1. Frequency = 4000 Hz
      2. Sound (Pure tone stimulus) = Presented at 10 dB below the threshold → Raised in 5 dB → Till the
      3. sound is heard.
      4. Keep increasing the sound by 5 dB – till heard for 1 minute
      5. Result:
        1. Mild = 10-15 dB
        2. Mod = 10 – 25 dB
        3. Severe = 30 dB

Extra Edge: Decay of > 30 dB: Pathognomic of retro cochlear hearing loss.

  1. Recruitment
    1. Definition: Abnormal rapid increased in loudness with increasing intensity.
      - Is associated with S.N.H.L. (Cochlear type)
    2. ABLB (Alternate Binaural Loudness balance test)
    3. Method: Uses specially designed audiometers, which can alternately send two tones of the same frequency in the two ears.
      1. P.S Deaf ear: Reference Ear
      2. Better ear: Variable ear

Disadvantage: Difference b/w the hearing thresholds of the two ears should be at least 25 dB.


One ear should be normal.

  1. SISI (Short increment sensitivity index)
    1. Method: Sound used:
      1. Intensity: 20 dB SL
      2. Frequency: 1000, 4000 Hz.
      3. Increments: 1 dB
      4. No of increments: 20
      5. Stimulus: 5 Sec
    2. ISI score = 70 – 100%: Cochlear pathology.
    3. Advantage : Can be performed in nearly all ears.
    4. Disadvantage: A cooperative patient required
      - Not used in very severe S.N.H.L.
  1. ​​Electrocochleography.
    1. This measures the electrical activity generated in the cochlea in response to a click stimulus.
    2. The responses obtained include the cochlear microphonics and the VIIIth nerve action potential.

Fig:  Brainstem audiogram

  1. a, Meniere’s disease with hearing loss of 50 dB. This is normal recording
  2. b, small acoustic neuroma with an average hearing loss of 40 dB
  1. ​​Acoustic reflex/Stapedial reflex

  1. Pathway
    1. Afferent pathway
      Stimulus (Sound) → Middle Ear → Cochlea → Auditory nerve → Cochlear nucleus → Sup. Olivary complex
    2. Efferent pathway
      I/L Ear & C/L Ear → Motor Nu. of the facial nerve → VII N. → N. To stapedius → Middle ear

P.S. Non Acoustic Reflex Test.

  1. Stimulation of Trigeminal nerve.
  2. Method: Air jet in the orbit or Light touching of the face: In front of the ear.
  3. Indication: To know the middle ear status of a very deaf ear.

Method of performing acoustic reflex test: Sound intensity used: 70 to 105 dB SL               

Absent Stapedial Reflex:


  1. Use of stapedial reflex test
    1. Elimination of M.E. pathology
    2. Differentiation between cochlear and retro cochlear pathology. (Acoustic reflex gets elicited at lower intensities due to recruitment)
    3. For detection of N.O.J.L.
    4. For identifying the level of lesion in VII N. Palsy
    5. Non invasive
      Used in
      1. Children
      2. Malinger
      3. Acoustic Schwannoma
      4. U/L complaint of Ear

I            -       distal VIII nerve

II           -       proximal VIII nerve

III          -       cochlear nuclear

IV          -       Superior olivary complex

V           -       Lateral LAMINA

VI / VII -       inferior colliculus

I     -       Acoustic nerve
II    -       Chochlear nerve
III   -       Superior olivary complex
IV   -       Lateral lemniscus
V   -       Inferior colliculus
VI   -       Medical geniculate ganglion

 I, III, and V are seen in newborn
 In acoustic neuroma, phase V prolonged
 Only 4 drugs affect BERA - Phenytoin, Halothane, Diazepam, Lidocaine

  1. ASSR (Auditory steady state response)
    1. ASSR is an objective test used for evaluation of hearing ability in children too young for traditional
    2. Audiometric testing.
    3. The results obtained from ASSR testing can be used to estimate the behavioral pure-tone audiogram.
    4. It evaluates 4 frequencies – 500, 1000, 2000 and 4000 Hz
    5. It is measured in nano volt         



i. The auditory system is excited while Stimulating 4 frequencies and both ears

i. The auditory system in excited by one tone and one at a time.



ii. Dependent on statistical analysis

ii. Dependent on subjective analysis

iii. Measured in nano volts

iii. Measured in micro volts

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