TYPES OF AUDIOMETRY
- Subjective Audiometry
- Pure Tone Audiometry,Speech audiometry,Bekesy Audiometry
- Objective Audiometry
- Immittance Audiometry,BERA,Electrocochleography,Otoacoustic Emission Audiometry.
PURE TONE AUDIOMETRY
- Pure tone audiometry is a subjective test used in the assessment of hearing
- The test can provide both bone and air conduction threshold.
- The frequency range tested includes 250Hz to 8kHz.
- There is also high frequency Pure Tone Audiometry covering the frequency range above 8000hz to 16,000hz,specifically for ototoxicity monitoring,
- The threshold of lower limit of normal is considered to be 20dB.
- Pure-tone average (PTA) is the average of hearing sensitivity at 500, 1000, and 2000 Hz.
USES OF PURE TONE AUDIOMETRY
- The usual primary purpose of pure-tone tests is to determine the type, degree, and configuration of hearing loss.
- Essential to prescribe a hearing aid.
- To find the degree of handicap for medicolegal purposes.
- To predict speech reception threshold.
PURE TONE AUDIOGRAM TYPICAL OF AUDITORY DISORDERS
- Presbyacusis: bilateral and symmetric sensorineural hearing loss. Usually, the higher frequencies are most severely affected.
- Otitis Media: flat or up-sloping conductive hearing loss. Word recognition usually is excellent
- Noise-induced hearing loss: greatest in the 4000- to 6000-Hz region.
- Otosclerosis :slowly progressive conductive or mixed hearing loss,Dip at 2000 Hz-Carhart’s Notch.
- Speech reception threshold (SRT): The minimum intensity at which 50% of words are repeated correctly by the patient
- Speech discrimination score: patients ability to understand speech
- Phonetically balanced (PB) words – single syllable words e.g. pin, day, bus are used
- Roll over phenomenon
- Seen in retrocochlear hearing loss
- With increase in speech intensity above a particular level, the PB word score falls rather than maintain a plateau as in cochlear type of lesions
Uses of Speech Audiometry
- To differentiate organic from functional hearing loss
- To find the intensity at which discrimination score is best which is helpful for fitting a hearing aid
- To differentiate cochlear from retrocochlear lesions
- Self-recording audiometry where various pure tone frequencies automatically move from low to high while the patient controls the intensity.
- Two tracings, one with continuous and and the other with pulsed tone are obtained.
Types of tracings obtained from Bekesy audiometry:
- Type I: Continuous and pulsed tracings overlap. Seen in normal hearing or conductive hearing loss.
- Type II: Continuous and pulsed tracings overlap up to 1000 Hz and then continuous tracing falls. Seen in cochlear loss.
- Type III: Continuous tracing falls below pulsed tracing at 100 to 500 Hz even up to 40-50 dB. Seen in retrocochlear/neural lesion.
- Type IV: Continuous tracing falls below pulsed lesion at frequencies up to 1000 Hz by more than 25 dB. Seen in retrocochlear/neural lesion.
- Type V: Continuous tracing is above pulsed one. Seen in non-organic hearing loss.
- Pure Tone Audiometry is a subjective type of Audiometry Test
- High frequency audiometry used to monitor hearing loss due to Ototoxicity.
- In Non-organic hearing loss continuous tracing above pulsed tracing is used in Bekesy audiometry.
- Pure tone audiogram with a dip at 2000 Hz(Carhart’s Notch) is characteristic of Otosclerosis.