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Audiology is the branch of medical science concerned with:
Hearing
Balance
Hearing disorders
Evaluation and rehabilitation of hearing impairment
It deals with:
Assessment of hearing
Prevention of hearing loss
Diagnosis of auditory disorders
Rehabilitation of deafness
Audiology includes:
Hearing assessment
Diagnosis of hearing disorders
Evaluation of vestibular disorders
Newborn hearing screening
Speech audiometry
Hearing aid fitting
Cochlear implant assessment
Rehabilitation of hearing-impaired patients
Occupational hearing conservation
Medico-legal hearing evaluation
Audiology is essential in ENT because it helps in:
Early detection of deafness
Differentiation of conductive and sensorineural hearing loss
Assessment of severity of hearing impairment
Localization of lesion:
Cochlear
Retrocochlear
Central
Monitoring ototoxicity
Evaluation before and after ear surgery
Hearing rehabilitation planning
Neonatal hearing screening
Audiology plays a major role in rehabilitation by:
Selection of hearing aids
Hearing aid fitting
Cochlear implant candidacy evaluation
Auditory training
Speech therapy support
Counseling of patients and parents
Educational rehabilitation in children
| Branch | Main Focus |
|---|---|
| Clinical audiology | Diagnosis of hearing disorders |
| Pediatric audiology | Hearing disorders in children |
| Industrial audiology | Occupational hearing conservation |
| Rehabilitation audiology | Hearing rehabilitation |
| Electrophysiological audiology | Objective hearing tests |
Concerned with:
Hearing assessment
Diagnosis of deafness
Tinnitus evaluation
Vestibular assessment
Common tests:
Pure tone audiometry
Speech audiometry
Tympanometry
OAE
BERA
Deals with hearing disorders in:
Neonates
Infants
Children
Newborn hearing screening
Congenital deafness detection
Developmental speech delay evaluation
Cochlear implant assessment
Concerned with occupational hearing conservation.
Noise level assessment
Worker screening
Prevention of NIHL
Hearing protection programs
Focuses on improving communication ability in hearing-impaired patients.
Hearing aids
Cochlear implants
Auditory verbal therapy
Lip reading
Counseling
Deals with objective hearing tests using electrical responses generated in auditory pathways.
BERA/ABR
ASSR
Electrocochleography
Cortical auditory evoked potentials
Ancient civilizations recognized deafness but lacked scientific evaluation.
Development accelerated after invention of acoustic physics.
Modern audiology developed during and after World War II due to rehabilitation needs of soldiers with hearing loss.
Whispered voice tests
Watch tick tests
Tuning fork tests
Electronic audiometers introduced in 20th century
Digital audiometers now widely used
Weber test
Rinne test
Schwabach test
Voice tests
These formed the basis of modern hearing evaluation.
Initial experiments began in 1950s.
Multichannel cochlear implants developed later.
Modern implants provide:
Better speech discrimination
Bilateral implantation
Improved rehabilitation
Neonatal hearing screening
School screening
Occupational screening
Type of hearing loss
Degree of hearing loss
Site of lesion
Hearing aids
Cochlear implants
Auditory training
Evaluation of workers exposed to noise
Prevention of industrial deafness
Compensation assessment
Disability certification
Detection of malingering
Sound is a form of mechanical energy produced by vibration of matter and transmitted through a medium as waves.
Sound is:
Mechanical
Longitudinal
Wave motion dependent
Requires a medium for transmission.
Cannot travel in vacuum.
Produced by vibration of objects.
Vibrating object causes:
Compression
Rarefaction
of surrounding particles.
Examples:
Vocal cord vibration
Tuning fork vibration
Particles vibrate parallel to direction of propagation.
Sound travels as:
Compression waves
Rarefaction waves
Region where particles are crowded together.
High pressure area.
Region where particles are spread apart.
Low pressure area.
| Medium | Velocity of Sound |
|---|---|
| Air | ~343 m/s |
| Water | ~1500 m/s |
| Steel | ~5000 m/s |
Sound travels fastest in solids.
Slowest in gases.
Velocity depends on:
Density
Elasticity
Temperature
Number of vibrations per second.
Unit = Hertz (Hz)
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Where:
f = frequency
T = time period
Determines pitch.
Human audible range:
20 Hz to 20,000 Hz
Speech frequencies:
500–4000 Hz
Amount of sound energy passing through unit area per second.
Watt/m²
Determines loudness sensation.
Proportional to square of amplitude.
I\propto A^2
Maximum displacement of vibrating particles from resting position.
Loudness
Higher amplitude → louder sound
Psychological perception of frequency.
→ High pitch
→ Low pitch
Subjective perception of sound intensity.
Intensity
Frequency
Duration of exposure
Characteristic feature allowing distinction between sounds of same pitch and loudness.
Depends on:
Harmonics
Overtones
Example:
Violin vs flute
Relationship between two sound waves in time.
Interference
Binaural hearing
Distance traveled per second by sound wave.
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Where:
v = velocity
f = frequency
λ = wavelength
Total sound energy emitted per second.
Capacity to perform work carried by sound waves.
Unit of frequency.
1 Hz = 1 cycle/second
Logarithmic unit of sound intensity ratio.
Rarely used clinically.
One-tenth of a bel.
dB=10\log_{10}\left(\frac{I_1}{I_0}\right)
Logarithmic scale.
Widely used in audiology.
Human hearing range:
0 dB to 120 dB
Measurement of sound pressure relative to reference pressure.
0.0002 dyne/cm²
or
20 micropascals
Human ear perceives sound logarithmically.
Allows large sound ranges to be expressed conveniently.
| Type | Description |
|---|---|
| Pure tone | Single frequency |
| Complex tone | Multiple frequencies |
| Noise | Random frequencies |
| White noise | Equal intensity across frequencies |
| Narrow band noise | Limited frequency range |
| Speech sound | Complex biologic sound |
Contains single frequency.
Produced by tuning fork.
Used in audiometry.
Contains multiple frequencies.
Example:
Speech
Musical instruments
Random mixture of frequencies.
Unpleasant and nonperiodic.
Equal energy at all frequencies.
Used in masking during audiometry.
Noise concentrated around limited frequencies.
Used in audiometric masking.
Complex sound made of:
Fundamental frequencies
Harmonics
Formants
Increased amplitude when vibration frequency equals natural frequency of object.
External auditory canal resonance
Frequencies that are integral multiples of fundamental frequency.
Frequencies above fundamental frequency.
Bouncing back of sound waves from surface.
Change in direction of sound wave due to change in medium.
Bending of sound waves around obstacles.
Conversion of sound energy into heat.
Persistence of sound after source stops due to repeated reflections.
Interaction between two sound waves.
Constructive
Destructive
Reduction in vibratory movement by resistance.
One sound reduces audibility of another sound.
Used in audiometry.
| Concept | Description |
|---|---|
| Free field | No reflections |
| Diffuse field | Multiple reflections |
| Near field | Close to sound source |
| Far field | Distant from source |
Most speech frequencies:
500–4000 Hz
Frequency bands important for speech recognition.
Smallest units of speech sound.
Banana-shaped area on audiogram where speech sounds occur.
Approximately:
300–3400 Hz
Lowest sound intensity heard by normal ear.
Smallest detectable change in sound intensity or frequency.
Curves showing intensity needed at different frequencies to produce equal loudness sensation.
Graphical representation of equal loudness contours.
Sound masks another sound occurring immediately before or after it.
Ability to identify location of sound source.
Advantages:
Sound localization
Better speech understanding
Hearing in noisy environment
Depends on:
Interaural time difference
Interaural intensity difference
Head blocks sound reaching opposite ear.
Important in localization.
Sound transmission through:
External ear
Tympanic membrane
Ossicles
Cochlea
Sound transmitted directly through skull bones to cochlea.
Ossicles lag behind skull vibration causing stapes movement.
Skull compression directly moves cochlear fluids.
Skull vibration causes movement of ear canal air which vibrates tympanic membrane.
Opposition offered to sound transmission.
Ease of sound transmission.
Mass
Stiffness
Friction
Middle ear converts sound from air medium to fluid medium efficiently.
Without impedance matching:
~99% sound energy lost.
Tympanic membrane area larger than stapes footplate.
Approximately 17:1
Increased pressure at oval window.
Lever action of malleus and incus increases force.
Approximately 1.3:1
Prevents cancellation of sound waves within cochlea.
Collects sound
Aids localization
Protects ear canal
Pinna funnels sound into external auditory canal.
Pinna helps determine vertical direction of sound.
External auditory canal amplifies:
2–4 kHz frequencies
Improves speech understanding.
Tympanic membrane vibrates with sound waves.
Maximum vibration:
Pars tensa
Sequence:
Sound wave strikes tympanic membrane
Membrane vibrates
Ossicular chain moves
Stapes footplate moves oval window
Cochlear fluid movement occurs
Hair cells stimulated
Ossicles act as a mechanical lever system.
They transmit vibrations from tympanic membrane to oval window.
Tympanic membrane vibrates
Malleus moves medially and laterally
Incus transmits movement
Stapes footplate moves in oval window
Pressure waves generated in cochlear fluids
| Ossicle | Movement |
|---|---|
| Malleus | Rotatory movement |
| Incus | Lever transmission |
| Stapes | Piston-like movement |
Formed by:
Anterior malleolar ligament
Posterior incudal ligament
Ossicles move as single rigid unit.
More complex vibratory patterns occur.
Attached to tympanic membrane.
Receives sound vibrations from tympanic membrane.
Transmits vibrations to incus.
Participates in impedance matching.
Helps maintain tension of tympanic membrane.
Acts as connecting link between malleus and stapes.
Transfers vibrations efficiently.
Participates in ossicular lever mechanism.
Footplate attached to oval window.
Converts ossicular vibrations into fluid waves in cochlea.
Piston-like movement creates pressure waves in perilymph.
Middle ear amplifies sound while transmitting from air medium to fluid medium.
Prevents loss of sound energy.
Improves hearing efficiency.
Without transformer mechanism:
Nearly 99% sound energy lost due to impedance mismatch.
Tympanic membrane area much larger than stapes footplate.
Approximately 17:1
Pressure amplification at oval window.
Handle of malleus longer than long process of incus.
Approximately 1.3:1
Increased force transmission.
Total amplification:
About 22 times
Approximately 25–30 dB gain
Prevents phase cancellation between oval and round windows.
Involuntary contraction of middle ear muscles in response to loud sound.
Stapedius muscle
Tensor tympani muscle
Stapedius
Cochlea
Cochlear nerve
Cochlear nucleus
Superior olivary complex
Facial nerve
Stapedius muscle
Protects cochlea from loud sounds
Reduces low-frequency sound transmission
Improves speech discrimination in noisy environment
Approximately:
70–90 dB above hearing threshold
Facial nerve assessment
Retrocochlear lesion detection
Tympanometry
Smallest skeletal muscle in body.
Supplied by:
Facial nerve
Pulls stapes posteriorly
Reduces stapes movement
Dampens loud sound transmission
Protects cochlea
→ Hyperacusis may occur.
Mandibular division of trigeminal nerve
Pulls malleus medially
Tenses tympanic membrane
Reduces tympanic membrane vibration
Less important than stapedius reflex in humans.
| Function | Role |
|---|---|
| Ventilation | Equalizes pressure |
| Protection | Prevents reflux |
| Clearance | Removes secretions |
Maintains equal air pressure on both sides of tympanic membrane.
Tube opens during:
Swallowing
Yawning
Sneezing
Normal tympanic membrane mobility
Proper sound conduction
Protects middle ear from:
Nasopharyngeal secretions
Loud sounds
Pathogens
Drains middle ear secretions into nasopharynx.
Mucociliary clearance
Middle ear → nasopharynx
Maintains atmospheric pressure within middle ear.
Ear blockage
Retraction of tympanic membrane
Conductive hearing loss
Otitis media with effusion
Cochlea is spiral-shaped.
Makes:
2.5 to 2.75 turns around modiolus.
Basal turn
Middle turn
Apical turn
Base:
High-frequency hearing
Apex:
Low-frequency hearing
Upper chamber of cochlea.
Contains:
Perilymph
Oval window
Middle cochlear duct.
Contains:
Endolymph
Organ of Corti
Lower chamber.
Contains:
Perilymph
Round window
Sensory organ of hearing situated on basilar membrane.
Inner hair cells
Outer hair cells
Pillar cells
Supporting cells
Tectorial membrane
Converts mechanical vibrations into electrical impulses.
Narrow and stiff at base
Broad and flexible at apex
Base responds to high frequencies.
Apex responds to low frequencies.
Gelatinous membrane overlying hair cells.
Causes bending of stereocilia during sound stimulation.
Separates:
Scala vestibuli
Scala media
Highly vascular epithelium in lateral wall of scala media.
Produces endolymph
Maintains ionic balance
Generates endocochlear potential
| Feature | Endolymph | Perilymph |
|---|---|---|
| Location | Scala media | Scala vestibuli & tympani |
| Major ion | Potassium | Sodium |
| Electrical charge | Positive | Similar to extracellular fluid |
Rich in potassium.
Secreted by stria vascularis.
Rich in sodium.
Similar to extracellular fluid.
High K+
Low Na+
High Na+
Low K+
Single row
Approximately 3500 cells
Primary sensory receptors for hearing.
90–95% auditory input
Three rows
Approximately 12,000 cells
Cochlear amplification
Frequency selectivity
Fine tuning of sound
Fine protein filaments connecting stereocilia.
Open ion channels during stereocilia deflection.
Sound causes basilar membrane movement
Stereocilia bend
Tip links open potassium channels
Potassium enters cell
Depolarization occurs
Neurotransmitter released
Auditory nerve stimulated
Potassium exits hair cells and returns to endolymph through supporting cells and stria vascularis.
Maintains cochlear ionic homeostasis.
Motor protein present in outer hair cells.
Causes electromotility of outer hair cells.
Active amplification mechanism mediated by outer hair cells.
Increases sensitivity
Improves frequency selectivity
Sound produces wave traveling along basilar membrane.
High frequencies:
Maximal displacement near base
Low frequencies:
Maximal displacement near apex
Different cochlear regions respond to different frequencies.
| Region | Frequency |
|---|---|
| Base | High frequency |
| Apex | Low frequency |
| Feature | Basal Cochlea | Apical Cochlea |
|---|---|---|
| Width | Narrow | Broad |
| Stiffness | High | Low |
| Frequency | High | Low |
Ability of cochlea to distinguish different frequencies.
Auditory nerve firing synchronized with sound wave phase.
Low-frequency hearing
Positive electrical potential in scala media.
Approximately +80 mV
Stria vascularis
Alternating current potential generated mainly by outer hair cells.
Direct current potential generated by hair cells during stimulation.
Compound action potential generated in auditory nerve fibers.
Different regions of basilar membrane respond to different frequencies.
Entire basilar membrane vibrates uniformly.
Frequency determined by auditory nerve firing rate.
Groups of neurons fire together to encode high frequencies.
Proposed by von Bekesy.
Sound creates traveling wave along basilar membrane.
Frequency represented by rate of neuronal firing.
Timing of neuronal firing represents sound frequency.
Frequency represented by site of maximal basilar membrane displacement.
Hair cells
Spiral ganglion
Cochlear nerve
Cochlear nuclei
Superior olivary complex
Lateral lemniscus
Inferior colliculus
Medial geniculate body
Auditory cortex
Contains first-order neurons of auditory pathway.
Modiolus
Formed by axons of spiral ganglion cells.
Carries impulses to brainstem.
Located at pontomedullary junction.
Dorsal cochlear nucleus
Ventral cochlear nucleus
First site receiving bilateral auditory input.
Sound localization
Binaural interaction
Ascending auditory tract in brainstem.
Midbrain auditory relay center.
Auditory reflexes
Sound processing
Thalamic relay station for auditory pathway.
Superior temporal gyrus
Heschl gyri (Brodmann areas 41 & 42)
Usually left hemisphere.
Speech interpretation
Language comprehension
Recognition and interpretation of spoken language.
Identification of:
Pitch
Loudness
Meaning of sound
Combines auditory input from both ears.
Localization
Hearing in noise
Ability to differentiate sounds.
Interpretation of meaningful speech.
Depends on:
Interaural time difference
Interaural intensity difference
Head shadow effect
Psychoacoustics is the study of psychological perception of sound.
It explains how sound is perceived and interpreted by human brain.
Abnormally rapid increase in perceived loudness with small increase in sound intensity.
Occurs due to cochlear hair cell damage, especially outer hair cells.
Damaged cochlea has:
Elevated threshold
Reduced dynamic range
Soft sounds not heard.
Slightly louder sounds become uncomfortably loud quickly.
Cochlear sensorineural hearing loss
Meniere disease
Presbycusis
| Test | Principle |
|---|---|
| SISI test | Small intensity increment detection |
| ABLB test | Loudness balancing between ears |
| Metz test | Acoustic reflex at low sensation level |
Suggests cochlear pathology.
Helps differentiate cochlear from retrocochlear lesions.
Absence or reduction of loudness recruitment.
Retrocochlear lesions
Auditory nerve pathology
Helps differentiate retrocochlear from cochlear lesions.
Same sound perceived differently in two ears.
| Type | Description |
|---|---|
| Diplacusis binauralis | Different pitch perception in two ears |
| Diplacusis monauralis | Single ear perceives two tones |
Cochlear pathology
Meniere disease
Sudden SNHL
Increased sensitivity to ordinary environmental sounds.
Facial nerve palsy
Cochlear disorders
Migraine
Autism spectrum disorders
Stapedius paralysis
→ Excess sound transmission.
Normal sounds become painful or intolerable.
Fear or aversion to sound.
Migraine
Psychiatric disorders
Anxiety states
| Feature | Hyperacusis | Phonophobia |
|---|---|---|
| Nature | Increased sound sensitivity | Fear of sound |
| Cause | Auditory dysfunction | Psychological/emotional |
| Pain | Common | Usually absent |
Temporary reduction in hearing sensitivity after prolonged sound exposure.
Temporary exhaustion of cochlear hair cells.
Hearing returns after rest.
Decrease in auditory nerve response during continuous sound stimulation.
Neural adaptation within auditory pathway.
Helps brain ignore constant background noise.
Ability to distinguish sounds of different frequencies.
Speech understanding
Music perception
Ability to detect small changes in loudness.
Approximately:
1 dB
| Term | Definition | Site |
|---|---|---|
| Recruitment | Rapid loudness growth | Cochlear lesion |
| Decruitment | Absence of recruitment | Retrocochlear lesion |
| Diplacusis | Different pitch perception | Cochlear lesion |
| Hyperacusis | Increased sound sensitivity | Stapedius/cochlea |
| Phonophobia | Fear of sound | Psychological |
| Auditory fatigue | Temporary threshold shift | Hair cell exhaustion |
| Auditory adaptation | Reduced neural response | Auditory pathway |
| Type | Site of Lesion |
|---|---|
| Conductive hearing loss | External/middle ear |
| Sensorineural hearing loss | Cochlea/auditory nerve |
| Mixed hearing loss | Conductive + sensorineural |
| Central hearing loss | Central auditory pathway |
| Functional hearing loss | No organic lesion |
Hearing loss due to impaired sound conduction through:
External ear
Tympanic membrane
Middle ear
Air conduction reduced
Bone conduction relatively preserved
Air-bone gap present
Speech discrimination usually normal
Hearing better in noisy environment (Paracusis Willisii)
Bone conduction near normal
Air conduction impaired
Hearing loss due to pathology of:
Cochlea
Hair cells
Auditory nerve
Both air and bone conduction reduced
No significant air-bone gap
Speech discrimination reduced
Recruitment present
Air and bone conduction both impaired.
Combination of:
Conductive hearing loss
Sensorineural hearing loss
Both air and bone conduction reduced
Air-bone gap present
Hearing disorder due to lesions in:
Brainstem auditory pathway
Auditory cortex
Difficulty understanding speech
Poor sound localization
Normal pure tone thresholds may occur
Apparent hearing loss without organic pathology.
Malingering
Psychogenic hearing loss
| Degree | Hearing Threshold |
|---|---|
| Mild | 26–40 dB |
| Moderate | 41–55 dB |
| Moderately severe | 56–70 dB |
| Severe | 71–90 dB |
| Profound | >90 dB |
Obstructs external auditory canal.
Sudden hearing reduction
Ear blockage sensation
Common in children
Canal obstruction causes sound conduction impairment.
Swelling and debris obstruct ear canal.
Pain
Discharge
Conductive hearing loss
Reduced vibrating surface area.
Size of perforation
Ossicular status
Middle ear fluid impairs ossicular movement.
Acute otitis media
OME
CSOM
Abnormal bone remodeling around stapes footplate.
Stapes fixation causes impaired sound transmission.
Carhart notch at 2 kHz
Trauma
CSOM
Cholesteatoma
Break in ossicular chain transmission.
| Site | Causes |
|---|---|
| External ear | Wax, foreign body, otitis externa |
| Tympanic membrane | Perforation |
| Middle ear | Otitis media, otosclerosis |
| Ossicles | Ossicular discontinuity |
Syndromic
Non-syndromic
TORCH infections
Ototoxic drugs
Birth asphyxia
Prematurity
Hyperbilirubinemia
Age-related bilateral progressive SNHL.
High-frequency loss
Difficulty understanding speech
Degeneration of:
Hair cells
Spiral ganglion
Stria vascularis
SNHL due to prolonged noise exposure.
4 kHz notch
Outer hair cell damage in basal cochlea.
Aminoglycosides
Cisplatin
Loop diuretics
Salicylates
Bilateral high-frequency SNHL
Tinnitus
Endolymphatic hydrops.
Fluctuating SNHL
Vertigo
Tinnitus
Vestibular schwannoma involving VIII nerve.
Unilateral SNHL
Poor speech discrimination
Tinnitus
Viral labyrinthitis
Meningitis
Syphilis
Mumps
Autoimmune inner ear disease
Cogan syndrome
| Cause | Mechanism |
|---|---|
| Presbycusis | Degeneration |
| NIHL | Hair cell damage |
| Ototoxicity | Hair cell toxicity |
| Meniere disease | Endolymphatic hydrops |
| Acoustic neuroma | VIII nerve compression |
| Infections | Cochlear damage |
Stroke
Multiple sclerosis
Tumors
Difficulty localizing sound
Auditory processing impairment
Temporal lobe auditory cortex
Auditory agnosia
Word deafness
Intentional feigning of hearing loss.
Compensation
Avoidance of duty
Medico-legal benefit
Stenger test
Lombard test
Bekesy audiometry
Hearing loss without detectable organic lesion.
Psychological disorders
Conversion reaction
| Feature | Conductive HL | Sensorineural HL |
|---|---|---|
| Site | External/middle ear | Cochlea/nerve |
| Air conduction | Reduced | Reduced |
| Bone conduction | Normal | Reduced |
| Air-bone gap | Present | Absent |
| Speech discrimination | Normal | Reduced |
| Recruitment | Absent | Present |
| Rinne test | Negative | Positive |
| Weber test | Lateralizes to affected ear | Lateralizes to better ear |
Recruitment → Cochlear lesion
Decruitment → Retrocochlear lesion
Carhart notch → Otosclerosis
4 kHz notch → Noise-induced hearing loss
Hyperacusis → Facial nerve palsy
Presbycusis → Bilateral high-frequency SNHL
Meniere disease → Fluctuating low-frequency SNHL
Acoustic neuroma → Unilateral SNHL with poor speech discrimination
Hearing loss
↓
Tuning fork tests
↓
Air-bone gap present
→ Conductive hearing loss
No air-bone gap
→ Sensorineural hearing loss
Speech discrimination poor
→ Retrocochlear suspicion
Tinnitus is perception of sound in the absence of an external acoustic stimulus.
Ringing
Buzzing
Roaring
Hissing
Clicking
Whistling
Pulsating sound
It is a symptom, not a disease.
May be:
Intermittent
Continuous
Unilateral
Bilateral
Sound perceived only by patient.
Most common type.
Usually due to abnormal neural activity within auditory system.
Cochlear disorders
SNHL
Presbycusis
Noise trauma
Ototoxicity
Meniere disease
Sound audible to both patient and examiner.
Produced by actual internal sound source.
Vascular abnormalities
Muscle spasm
Patulous Eustachian tube
| Feature | Subjective | Objective |
|---|---|---|
| Heard by examiner | No | Yes |
| Frequency | Very common | Rare |
| Cause | Neural/cochlear | Mechanical/vascular |
| Example | Presbycusis | Glomus tumor |
Wax
Foreign body
Otitis externa
Otitis media
Otosclerosis
Eustachian tube dysfunction
Presbycusis
Noise-induced hearing loss
Meniere disease
Sudden SNHL
Labyrinthitis
Acoustic neuroma
Multiple sclerosis
Head injury
Migraine
Temporal lobe lesions
Usually vascular in origin.
Glomus tumor
AV malformation
Carotid stenosis
Hypertension
Venous hum
Aneurysm
Palatal myoclonus
Stapedius spasm
Tensor tympani spasm
Aminoglycosides
Salicylates
Loop diuretics
Cisplatin
Quinine
| Category | Examples |
|---|---|
| Otological | Presbycusis, Meniere disease |
| Neurological | Multiple sclerosis |
| Vascular | Glomus tumor |
| Muscular | Palatal myoclonus |
| Drug-induced | Salicylates |
Damage to hair cells causes abnormal spontaneous neural activity.
Outer hair cell dysfunction
Abnormal neurotransmitter release
Reduced auditory input
Increased spontaneous firing
Presbycusis
NIHL
Ototoxicity
Reduced cochlear input causes central auditory pathway hyperactivity.
Increased neuronal gain
Neural plasticity
Cortical reorganization
Explains persistent tinnitus even after cochlear destruction.
Sudden
Gradual
Intermittent
Continuous
Ringing
Buzzing
Pulsatile
Clicking
Unilateral
Bilateral
Hearing loss
Vertigo
Ear fullness
Headache
Noise exposure
Stress
Fatigue
Ototoxic drugs
Noise exposure
Anxiety
Depression
Sleep disturbance
Wax
Tympanic membrane
Middle ear disease
Especially:
Facial nerve
Vestibulocochlear nerve
Bruits
Pulsatile neck masses
Temporomandibular joint dysfunction may cause tinnitus.
Cerebellar signs
Brainstem signs
Detects hearing loss pattern.
Speech discrimination assessment.
Middle ear evaluation.
Hair cell function.
Retrocochlear lesion evaluation.
Determines tinnitus frequency.
Determines tinnitus intensity.
Determines masking level needed to suppress tinnitus.
Temporary suppression of tinnitus after masking sound.
Assesses severity and quality-of-life impact.
Identify treatable cause.
Reduce symptom severity.
Improve quality of life.
Essential component of treatment.
Explanation of benign nature
Stress reduction
Sleep hygiene
Coping strategies
External sound reduces tinnitus perception.
White noise generators
Environmental sound enrichment
Smartphone applications
Reduces contrast between tinnitus and silence.
Combination of:
Counseling
Sound therapy
Habituation to tinnitus.
Brain gradually ignores tinnitus signal.
Improve hearing
Reduce tinnitus awareness
Increase environmental sound input
Presbycusis
SNHL-associated tinnitus
Anxiolytics
Antidepressants
Sedatives
Melatonin
No universally curative drug exists.
| Cause | Treatment |
|---|---|
| Wax | Removal |
| Otitis media | Antibiotics |
| Otosclerosis | Surgery/hearing aid |
| Meniere disease | Salt restriction, betahistine |
| Acoustic neuroma | Surgery/radiotherapy |
Temporary suppression or reduction of tinnitus following exposure to masking sound.
Temporary reduction of abnormal neural activity.
Suggests better response to sound therapy.
Rhythmic tinnitus synchronous with heartbeat.
Glomus tumor
Carotid stenosis
AV malformation
Idiopathic intracranial hypertension
Unilateral pulsatile tinnitus requires vascular evaluation.
| Feature | Possible Serious Cause |
|---|---|
| Unilateral tinnitus | Acoustic neuroma |
| Pulsatile tinnitus | Vascular lesion |
| Associated neurological signs | CNS pathology |
| Sudden SNHL | Otological emergency |
| Feature | Subjective | Objective |
|---|---|---|
| Heard by patient | Yes | Yes |
| Heard by examiner | No | Yes |
| Commonness | Very common | Rare |
| Cause | Neural/cochlear | Mechanical/vascular |
Most common type → Subjective tinnitus
Pulsatile tinnitus → Usually vascular
Stapedius spasm → Objective tinnitus
Presbycusis → Common cause in elderly
Acoustic neuroma → Unilateral tinnitus with SNHL
Residual inhibition → Temporary tinnitus suppression after masking
TRT = Counseling + sound therapy
No universally curative drug for tinnitus
Tinnitus
↓
Pulsatile?
→ Yes → Vascular evaluation
No
↓
Associated hearing loss?
→ Audiometry
Unilateral SNHL
→ MRI for acoustic neuroma
Bilateral SNHL
→ Presbycusis/NIHL likely
Noise pollution is unwanted or excessive sound that adversely affects hearing and health.
High intensity
Prolonged exposure
Intermittent or continuous
High-frequency noise more harmful
Factory machinery
Textile mills
Mining equipment
Aircraft engines
Construction machinery
Traffic
Loudspeakers
Music systems
Airports
Urban crowd noise
| Type | Examples |
|---|---|
| Continuous noise | Factory machines |
| Intermittent noise | Traffic |
| Impulse noise | Explosion, gunfire |
Sensorineural hearing loss caused by prolonged exposure to excessive noise.
Usually bilateral
Symmetrical
Irreversible
Predominantly affects high frequencies
Outer hair cells of basal turn of cochlea
Mechanical damage
Metabolic exhaustion
Oxidative stress
Hair cell degeneration
Outer hair cells
Inner hair cells
Spiral ganglion
Auditory nerve fibers
4 kHz region
Reason:
Maximum cochlear vulnerability at basal turn.
Sudden hearing loss due to single intense sound exposure.
Explosion
Gunfire
Blast injury
Tympanic membrane rupture
Ossicular disruption
Cochlear hair cell injury
Temporary elevation of hearing threshold after noise exposure.
Hair cell exhaustion
Metabolic fatigue
Usually within hours to days.
Warning sign of cochlear injury.
Irreversible hearing loss due to permanent cochlear damage.
Hair cell destruction
Neural degeneration
Permanent NIHL
Characteristic dip at 4 kHz on audiogram.
Hallmark of NIHL
Basal turn most vulnerable to acoustic trauma.
External auditory canal resonance amplifies around 3–4 kHz.
Difficulty hearing in noisy environment
Tinnitus
Temporary ear fullness
Progressive hearing loss
Difficulty understanding speech
Permanent tinnitus
Bilateral symmetrical SNHL
4 kHz notch
High-frequency hearing loss
Initially affects:
3–6 kHz
Later spreads to speech frequencies.
| Feature | Finding |
|---|---|
| Type | Sensorineural |
| Symmetry | Bilateral |
| Frequency affected | High frequency |
| Classical notch | 4 kHz |
Noise assessment
Periodic audiometry
Worker education
Engineering controls
Hearing protection devices
Soundproofing
Machine maintenance
Noise barriers
Vibration reduction
Limiting exposure duration
Worker rotation
Quiet rest periods
Inserted into external auditory canal.
Cover entire external ear.
Partial ear canal protection.
| Device | Advantage | Disadvantage |
|---|---|---|
| Ear plugs | Cheap, portable | Improper fitting |
| Ear muffs | Better protection | Bulky |
| Canal caps | Easy use | Less effective |
Occupational noise exposure should be monitored.
Hearing conservation program mandatory for:
≥85 dB exposure over 8 hours
| Noise Level | Maximum Daily Exposure |
|---|---|
| 85 dB | 8 hours |
| 90 dB | 4 hours |
| 95 dB | 2 hours |
| 100 dB | 1 hour |
| Feature | NIHL |
|---|---|
| Type | SNHL |
| Ear involved | Bilateral |
| Ear structure affected | Outer hair cells |
| Characteristic audiogram | 4 kHz notch |
| Reversibility | Irreversible |
| Prevention | Hearing protection |
| Feature | Acoustic Trauma | NIHL |
|---|---|---|
| Exposure | Sudden | Chronic |
| Cause | Explosion | Continuous noise |
| Hearing loss | Sudden | Gradual |
| Tympanic membrane rupture | Common | Rare |
Ototoxicity is damage to inner ear or auditory nerve caused by drugs or chemicals.
Cochlea
Vestibular apparatus
Auditory nerve
Gentamicin
Streptomycin
Amikacin
Tobramycin
| Drug | Predominant Toxicity |
|---|---|
| Streptomycin | Vestibular |
| Gentamicin | Vestibular |
| Amikacin | Cochlear |
| Neomycin | Severe cochlear toxicity |
Renal failure
Prolonged therapy
High dose
Concurrent ototoxic drugs
Severe cochlear toxicity
Bilateral high-frequency SNHL
Dose-dependent
Oxidative stress
Hair cell apoptosis
Furosemide
Ethacrynic acid
Usually reversible hearing loss
Affects stria vascularis
Reversible tinnitus
Reversible SNHL
Outer hair cell dysfunction
Quinine
Chloroquine
Tinnitus
Hearing loss
Vertigo
| Drug | Main Toxicity |
|---|---|
| Aminoglycosides | Cochlear/vestibular |
| Cisplatin | Cochlear |
| Loop diuretics | Cochlear |
| Salicylates | Reversible tinnitus |
| Antimalarials | Cochlear + vestibular |
Outer hair cells affected first.
Basal turn commonly involved.
Reactive oxygen species damage cochlear cells.
Cellular energy failure causes apoptosis.
Spiral ganglion degeneration may occur.
Basal turn most susceptible to toxic injury.
Tinnitus
High-frequency hearing loss
Difficulty understanding speech
Vertigo
Imbalance
Oscillopsia
Bilateral symmetrical SNHL
High-frequency loss initially
Progressive hearing loss after drug use
Associated renal impairment
Tinnitus preceding hearing loss
Detect early ototoxicity before permanent damage.
Before starting ototoxic drugs:
PTA
High-frequency audiometry
OAE
Serial audiometry
OAE monitoring
Vestibular assessment if needed
High-frequency hearing loss
OAE abnormalities
Avoid unnecessary ototoxic drugs.
Especially in renal impairment.
Avoid multiple ototoxic agents together.
Early detection prevents progression.
Use safer alternatives whenever possible.
| Drug | Important Point |
|---|---|
| Gentamicin | Vestibulotoxic |
| Amikacin | Cochleotoxic |
| Cisplatin | Severe high-frequency SNHL |
| Salicylates | Reversible tinnitus |
| Loop diuretics | Usually reversible |
| Feature | NIHL | Ototoxicity |
|---|---|---|
| Cause | Noise | Drugs |
| Audiogram | 4 kHz notch | High-frequency SNHL |
| Symmetry | Bilateral | Bilateral |
| Reversibility | Permanent | Variable |
| Main pathology | Hair cell trauma | Hair cell toxicity |
Patient on ototoxic drug
↓
Tinnitus/high-frequency hearing loss
↓
Baseline + serial audiometry
↓
OAE changes
↓
Dose reduction/alternative drug
↓
Prevent permanent SNHL
Most important step in evaluation of hearing loss.
Helps identify:
Type of hearing loss
Duration
Etiology
Progression
Need for further investigations
Suggests:
Sudden SNHL
Acoustic trauma
Viral labyrinthitis
Vascular causes
Suggests:
Presbycusis
Otosclerosis
Chronic otitis media
Noise-induced hearing loss
Acute
Chronic
Progressive
Fluctuating
Seen in:
Presbycusis
Otosclerosis
Acoustic neuroma
Seen in:
Meniere disease
| Symptom | Suggestive Condition |
|---|---|
| Tinnitus | SNHL, Meniere disease |
| Vertigo | Labyrinthine disorder |
| Ear discharge | CSOM |
| Ear pain | Otitis externa/media |
| Facial weakness | Facial nerve pathology |
| Headache | Intracranial pathology |
NIHL
Occupational hearing loss
Factory work
Firearms
Music exposure
Industrial machinery
Aminoglycosides
Cisplatin
Loop diuretics
Salicylates
Ask about:
Prematurity
Birth asphyxia
NICU stay
Hyperbilirubinemia
TORCH infection
Important in:
Congenital deafness
Otosclerosis
Genetic syndromes
Wax
Foreign body
Tympanic membrane perforation
Retraction
Middle ear effusion
Cholesteatoma
Facial nerve
Vestibulocochlear nerve
Facial asymmetry
Weakness
Hyperacusis
Nystagmus
Gait disturbance
Romberg sign
Past pointing
Compare:
Air conduction (AC)
Bone conduction (BC)
Helps differentiate:
Conductive hearing loss
Sensorineural hearing loss
| Frequency | Usefulness |
|---|---|
| 256 Hz | Too much vibration |
| 512 Hz | Best frequency |
| 1024 Hz | Tone decays rapidly |
Less tactile vibration
Longer persistence than 1024 Hz
Not easily affected by ambient noise
Most accurate clinically
Compares air conduction and bone conduction.
Vibrating tuning fork placed on mastoid.
Patient indicates when sound no longer heard.
Fork immediately placed near external auditory canal.
AC > BC
Positive Rinne
| Result | Interpretation |
|---|---|
| AC > BC | Normal/SNHL |
| BC > AC | Conductive hearing loss |
Severe unilateral SNHL interpreted falsely as conductive hearing loss.
Sound crosses skull to opposite normal ear.
Mask opposite ear.
Tests lateralization of sound.
Vibrating tuning fork placed on forehead or vertex.
| Finding | Interpretation |
|---|---|
| Central | Normal |
| Lateralizes to affected ear | Conductive HL |
| Lateralizes to better ear | SNHL |
Compares patient bone conduction with examiner.
Fork placed on patient mastoid.
When patient stops hearing:
Examiner places fork on own mastoid.
| Finding | Interpretation |
|---|---|
| Examiner hears longer | SNHL |
| Same duration | Normal |
Compares patient BC with normal examiner BC.
| Result | Meaning |
|---|---|
| Prolonged Schwabach | Conductive HL |
| Reduced Schwabach | SNHL |
Occlusion effect.
External auditory canal alternately closed and opened during BC testing.
| Result | Interpretation |
|---|---|
| Sound louder on occlusion | Normal/SNHL |
| No change | Conductive HL |
Assesses stapes mobility.
Air pressure applied in ear canal during BC hearing.
| Result | Meaning |
|---|---|
| Sound reduced with pressure | Normal |
| No change | Stapes fixation (otosclerosis) |
Subjective
Cannot quantify hearing loss accurately
Less reliable in bilateral hearing loss
Difficult in children
Requires cooperative patient
| Test | Main Use |
|---|---|
| Rinne | Compare AC vs BC |
| Weber | Lateralization |
| ABC | Bone conduction comparison |
| Schwabach | Duration of BC |
| Bing | Occlusion effect |
| Gelle | Stapes mobility |
PTA is subjective measurement of hearing thresholds for pure tones.
Determines minimum sound intensity heard at different frequencies.
| Part | Function |
|---|---|
| Oscillator | Generates tones |
| Attenuator | Controls intensity |
| Earphones | AC testing |
| Bone vibrator | BC testing |
| Microphone | Speech testing |
Requires patient response.
PTA
Speech audiometry
No patient response needed.
BERA
OAE
ASSR
Tests:
Entire auditory pathway
Usually 250–8000 Hz
Tests:
Cochlea directly
Usually 250–4000 Hz
Lowest intensity heard at least 50% of times.
Graphical representation of hearing thresholds.
| Axis | Represents |
|---|---|
| X-axis | Frequency |
| Y-axis | Hearing threshold in dB |
| Symbol | Meaning |
|---|---|
| O | Right AC |
| X | Left AC |
| < | Right BC |
| > | Left BC |
Air-bone gap present.
Both AC and BC reduced.
No air-bone gap.
Both reduced with air-bone gap.
| Pattern | Condition |
|---|---|
| Flat loss | Conductive HL |
| High-frequency loss | Presbycusis |
| Low-frequency loss | Meniere disease |
| Notch at 4 kHz | NIHL |
Dip at 2 kHz.
Seen in otosclerosis.
Dip at 4 kHz.
Seen in NIHL.
Mid-frequency SNHL.
Often hereditary.
Seen in:
Presbycusis
Ototoxicity
NIHL
Noise presented to non-test ear to prevent crossover hearing.
Masking increased until threshold stabilizes.
Excessive masking crosses to test ear.
Inadequate masking allows crossover.
Quantifies hearing loss
Determines type of hearing loss
Monitors progression
Hearing aid fitting
Medico-legal assessment
Subjective test
Requires cooperation
Difficult in infants
Cannot assess retrocochlear pathology reliably
Short Increment Sensitivity Index
Detects ability to perceive small intensity increments.
| Result | Meaning |
|---|---|
| High score | Cochlear lesion |
| Low score | Retrocochlear lesion |
Alternate Binaural Loudness Balance Test
Compares loudness growth between ears.
Recruitment present in cochlear lesions.
Acoustic reflex occurs at low sensation level in recruitment.
Measures auditory nerve fatigue.
Suggests retrocochlear lesion.
Automatic audiometry with continuous and interrupted tones.
Cochlear vs retrocochlear differentiation
Speech discrimination worsens at high intensity.
Retrocochlear lesions
Stenger phenomenon
Detect unilateral malingering.
Voice intensity increases in background noise.
Detects unilateral nonorganic hearing loss.
Delayed feedback disrupts speech in normal hearing.
Speech discrimination under noise conditions.
Minimum intensity at which speech detected.
Ability to understand speech correctly.
Lowest intensity at which 50% spondee words recognized.
Percentage of correctly identified words.
Intensity level most comfortable for speech listening.
Intensity becoming uncomfortable.
Reflect normal speech phoneme distribution.
Two-syllable words with equal stress.
Example:
Baseball
Toothbrush
SDS decreases with increased intensity.
Hearing aid fitting
Cochlear vs retrocochlear differentiation
Speech understanding assessment
Measures tympanic membrane mobility with changing air pressure.
| Component | Function |
|---|---|
| Probe tone | Sound stimulus |
| Air pump | Pressure variation |
| Microphone | Measures reflected sound |
Probe inserted in external auditory canal.
Pressure altered.
Compliance measured.
Measures ear canal space.
Mobility of tympanic membrane and ossicles.
Pressure at maximum compliance.
Normal middle ear function.
Shallow peak.
Reduced compliance.
Seen in otosclerosis.
Deep peak.
Hypermobile tympanic membrane.
Flat curve.
Middle ear effusion/perforation.
Negative pressure peak.
Eustachian tube dysfunction.
Stimulus and recording from same ear.
Stimulus and recording from opposite ear.
Decline in reflex during sustained stimulus.
Suggests:
Retrocochlear lesion
Middle ear evaluation
Otitis media with effusion
Otosclerosis diagnosis
Facial nerve assessment
Retrocochlear lesion screening
Eustachian tube dysfunction assessment
512 Hz tuning fork preferred clinically
False negative Rinne → Severe unilateral SNHL
Carhart notch → Otosclerosis
4 kHz notch → NIHL
Type B tympanogram → Middle ear effusion
Type C tympanogram → Eustachian tube dysfunction
Roll-over phenomenon → Retrocochlear lesion
High SISI score → Cochlear lesion
Objective hearing tests assess auditory function without requiring active patient response.
Useful in:
Infants
Uncooperative patients
Malingering
Comatose patients
| Test | Main Structure Assessed |
|---|---|
| OAE | Outer hair cells |
| BERA/ABR | Auditory nerve & brainstem |
| Electrocochleography | Cochlea |
| ASSR | Frequency-specific hearing threshold |
| Cortical responses | Higher auditory cortex |
OAE are low-intensity sounds generated by cochlea, mainly by outer hair cells.
Healthy outer hair cells exhibit electromotility.
This produces acoustic energy measurable in external auditory canal.
→ Basilar membrane vibration
→ Outer hair cell movement
→ Reverse traveling wave generated
→ Sound emitted into ear canal
→ Recorded by sensitive microphone
Outer hair cells
Presence of OAE indicates:
Normal outer hair cell function
Hearing threshold usually better than 30 dB
| Type | Full Form |
|---|---|
| TEOAE | Transient Evoked OAE |
| DPOAE | Distortion Product OAE |
Transient Evoked Otoacoustic Emission
Evoked by brief acoustic stimuli:
Clicks
Tone bursts
Rapid screening test
Useful in newborn hearing screening
Mainly 1–4 kHz
Distortion Product Otoacoustic Emission
Two simultaneous tones produce distortion products in cochlea.
More frequency-specific
Better for high-frequency assessment
f1 and f2 tones
| Feature | TEOAE | DPOAE |
|---|---|---|
| Stimulus | Clicks | Two tones |
| Frequency specificity | Less | More |
| Screening | Excellent | Good |
| High-frequency assessment | Less useful | Better |
Most common application.
Detects early outer hair cell damage.
Early cochlear injury assessment.
Presence of OAE suggests normal cochlear function.
OAE present
BERA absent/abnormal
Cannot assess auditory nerve.
Affected by:
Middle ear pathology
Ear canal blockage
Noise
| Finding | Interpretation |
|---|---|
| Present OAE | Normal outer hair cells |
| Absent OAE | Cochlear pathology/middle ear disease |
| Present OAE + absent BERA | Auditory neuropathy |
BERA records electrical activity generated in auditory nerve and brainstem following acoustic stimulation.
Sound stimulus produces synchronized neural responses.
These responses recorded using scalp electrodes.
Click stimulus
Tone burst
Earphones
Electrodes
Amplifier
Computer averaging system
Waves I–VII occur within first 10 ms.
| Wave | Generator |
|---|---|
| I | Distal auditory nerve |
| II | Proximal auditory nerve |
| III | Cochlear nucleus |
| IV | Superior olivary complex |
| V | Lateral lemniscus/inferior colliculus |
Wave V
Most stable and clinically useful.
Time interval between stimulus and appearance of specific wave.
| Wave | Approximate Latency |
|---|---|
| I | 1.5 ms |
| III | 3.5 ms |
| V | 5.5 ms |
Time difference between two waves.
| Interpeak | Significance |
|---|---|
| I–III | Lower brainstem conduction |
| III–V | Upper brainstem conduction |
| I–V | Total brainstem conduction |
Sharp peaks
Reproducible waveforms
Consistent latency
Delayed latency
Poorly formed waves
Absent waves
| Factor | Effect |
|---|---|
| Age | Neonates have prolonged latency |
| Temperature | Hypothermia prolongs latency |
| Hearing loss | Delayed/absent waves |
| Sedatives | Minimal effect |
| Neurological disease | Latency abnormalities |
All waves delayed equally.
Interpeak latency normal.
Delayed absolute latency.
Interpeak latency normal.
Prolonged interpeak latency.
Wave V delay/absence.
Especially high-risk neonates.
Acoustic neuroma diagnosis.
Useful in infants and uncooperative patients.
Multiple sclerosis
Brainstem tumors
During neurosurgery
| Feature | OAE | BERA |
|---|---|---|
| Structure assessed | Outer hair cells | Auditory nerve/brainstem |
| Patient cooperation | Not required | Not required |
| Newborn screening | Yes | Yes |
| Retrocochlear lesions | No | Yes |
Records electrical potentials generated within cochlea and auditory nerve.
Cochlear microphonics
Summating potential (SP)
Action potential (AP)
Ratio of summating potential to action potential.
Increased SP/AP ratio suggests:
Endolymphatic hydrops
Meniere disease
Elevated SP/AP ratio
Confirms cochlear hydrops.
Auditory Steady State Response
Continuous modulated tones evoke steady electrical responses in auditory pathway.
Frequency-specific objective hearing test.
Useful in severe hearing loss.
Estimates hearing threshold at multiple frequencies simultaneously.
Better in profound hearing loss.
Pediatric hearing assessment
Hearing aid fitting
Cochlear implant evaluation
Severe/profound SNHL assessment
Auditory evoked potentials occurring within:
10–50 ms after stimulus.
Thalamocortical auditory pathways.
Central auditory pathway assessment.
Auditory responses occurring after:
50 ms
Auditory cortex
Higher auditory function assessment
Central auditory processing disorders
Cognitive auditory evoked potential occurring around 300 ms.
Patient recognizes infrequent target stimulus among frequent stimuli.
Measures cognitive auditory processing.
Dementia
Psychiatric disorders
Cognitive dysfunction
Central auditory disorders
Auditory responses generated from auditory cortex.
Long latency responses
Reflect conscious auditory perception
Assessment of cortical auditory function
Pediatric hearing threshold estimation
Central auditory processing evaluation
| Test | Main Site Assessed | Main Use |
|---|---|---|
| OAE | Outer hair cells | Newborn screening |
| BERA | Auditory nerve & brainstem | Retrocochlear lesions |
| ECoG | Cochlea | Meniere disease |
| ASSR | Frequency-specific hearing | Severe SNHL |
| MLR | Thalamocortical pathways | Central auditory disorders |
| LLR | Auditory cortex | Cortical function |
| P300 | Cognitive auditory processing | Cognitive disorders |
OAE assesses outer hair cell function.
Present OAE + absent BERA → Auditory neuropathy.
Most stable BERA wave → Wave V.
Acoustic neuroma → Increased interpeak latency.
Elevated SP/AP ratio → Meniere disease.
ASSR useful in profound SNHL.
P300 evaluates cognitive auditory processing.
Suspected hearing loss
↓
Need cochlear assessment
→ OAE/ECoG
Need brainstem assessment
→ BERA
Need frequency-specific threshold
→ ASSR
Need cortical assessment
→ LLR/P300
Pediatric audiology deals with:
Detection
Evaluation
Rehabilitation of hearing disorders in infants and children.
Early hearing detection is essential for:
Speech development
Language acquisition
Cognitive development
Social interaction
Screening of all newborns for hearing loss irrespective of risk factors.
Early diagnosis before:
3 months of age
Early intervention before:
6 months of age
Congenital hearing loss may not be clinically obvious at birth.
Early rehabilitation improves speech outcome.
| Test | Main Structure Assessed |
|---|---|
| OAE | Outer hair cells |
| BERA/AABR | Auditory nerve & brainstem |
Detects otoacoustic emissions generated by outer hair cells.
Fast
Noninvasive
Easy bedside test
Misses auditory neuropathy
Affected by middle ear fluid
Measures auditory brainstem electrical responses.
Detects auditory neuropathy
More accurate
More time-consuming
Costlier
OAE screening
↓
Pass
→ Normal follow-up
Refer
→ Repeat OAE/BERA
Direct BERA/AABR preferred.
Mechanical ventilation
Sepsis
Prematurity
Toxoplasmosis
Rubella
CMV
Herpes simplex
Bilirubin neurotoxicity affects auditory pathway.
Genetic deafness risk.
Examples:
Microtia
Atresia
Cleft palate
Low birth weight
Ototoxic drugs
Meningitis
Birth asphyxia
Below 6 months
Observe behavioral response to sound.
Eye widening
Startle reflex
Crying cessation
6 months to 2 years
Child conditioned to turn toward sound source.
Visual reward given.
Child learns to localize sound source.
Around 6–24 months
2–5 years
Child performs play activity after hearing sound.
Examples:
Dropping block in box
Placing ring on peg
Child rewarded with toy/object after correct response.
| Age | Preferred Test |
|---|---|
| 0–6 months | BOA |
| 6 months–2 years | VRA/COR |
| 2–5 years | Play audiometry |
| >5 years | PTA |
| Category | Causes |
|---|---|
| Genetic | Syndromic/nonsyndromic |
| Prenatal | TORCH infection |
| Perinatal | Birth asphyxia |
| Postnatal | Meningitis |
Hearing loss associated with systemic abnormalities.
| Syndrome | Features |
|---|---|
| Usher syndrome | Deafness + retinitis pigmentosa |
| Waardenburg syndrome | White forelock + deafness |
| Pendred syndrome | Goiter + SNHL |
| Alport syndrome | Renal disease + deafness |
Isolated hereditary hearing loss without systemic abnormalities.
Autosomal recessive nonsyndromic SNHL
Early intervention critical for normal speech development.
Used in mild to severe hearing loss.
Used in severe/profound SNHL not benefitting from hearing aids.
Essential for language development.
Includes:
Audiologist
ENT surgeon
Speech therapist
Psychologist
Educator
Disorder characterized by:
Preserved outer hair cell function
Abnormal auditory nerve transmission
Prematurity
Hyperbilirubinemia
Genetic mutations
Hypoxia
Neuropathy disorders
Poor speech discrimination
Hearing fluctuation
Delayed speech development
| Test | Finding |
|---|---|
| OAE | Present |
| BERA | Abnormal/absent |
| PTA | Variable |
OAE present
BERA absent/abnormal
Important cause of failed speech perception despite hearing aid use.
Impaired processing of auditory information within central auditory nervous system despite normal peripheral hearing.
Difficulty understanding speech in noise
Poor auditory attention
Learning difficulties
Delayed language development
Speech audiometry
Dichotic listening tests
Auditory processing tests
Electrophysiological tests
Detect hearing loss early in school children.
OME
Wax
SNHL
Detect NIHL in workers.
Periodic audiometry
Noise monitoring
Early identification of hearing impairment in population.
Neonatal screening
Rural camps
School screening
Electronic device that amplifies sound to improve hearing.
| Component | Function |
|---|---|
| Microphone | Converts sound into electrical signals |
| Amplifier | Amplifies signal |
| Receiver | Converts electrical signal back to sound |
| Battery | Power source |
Receives sound waves.
Converts acoustic energy to electrical energy.
Increases signal intensity.
Converts electrical energy back to sound.
Provides power supply.
Difference between hearing aid output and input.
Gain=Output-Input
Maximum sound intensity produced by hearing aid.
Reduces excessive amplification of loud sounds.
Range of frequencies amplified.
Whistling sound due to sound leakage and re-amplification.
Larger device connected by wire.
Device behind ear connected to earmold.
Most commonly used
Suitable for children
Powerful amplification
Entire device within external ear.
Smaller and less visible.
Deeply placed in ear canal.
Cosmetically better.
Receiver placed inside canal.
Better sound quality.
Digital signal processing
Noise reduction
Directional microphones
Better speech clarity
| Type | Advantage | Disadvantage |
|---|---|---|
| BTE | Powerful | Visible |
| CIC | Cosmetic | Limited power |
| RIC | Better sound | Costly |
Measures actual sound delivered in ear canal.
Measures hearing aid performance for speech sounds.
Mild to severe SNHL
Conductive hearing loss not surgically correctable
Mixed hearing loss
Profound deafness with no benefit
Active ear discharge
Severe cognitive dysfunction
Bone Anchored Hearing Aid
Sound transmitted directly through skull bone to cochlea.
External auditory canal atresia
Chronic ear discharge
Conductive hearing loss
Single-sided deafness
Implantable device transmitting vibration to skull.
Better sound quality
Avoids occlusion of ear canal
Mechanical vibration delivered directly to ossicles.
Patients unable to tolerate conventional hearing aids.
Hearing aids
Cochlear implant
Speech therapy
Auditory training
Counseling
| Finding | Diagnosis |
|---|---|
| OAE present + BERA absent | ANSD |
| 4–6 month infant | VRA preferred |
| Severe congenital SNHL | Cochlear implant candidate |
| NICU stay | High-risk infant |
BTE most commonly used in children.
Digital hearing aids provide better speech clarity.
BAHA bypasses external and middle ear.
Real ear measurement checks actual hearing aid performance.
Newborn
↓
OAE screening
↓
Pass → Routine follow-up
Refer
↓
BERA
↓
Diagnosis
↓
Early rehabilitation
Cochlear implant is an electronic prosthetic device that bypasses damaged cochlear hair cells and directly stimulates auditory nerve fibers.
Sound
↓
Microphone receives sound
↓
Speech processor converts sound into digital signals
↓
Signals transmitted to internal receiver
↓
Electrode array stimulates cochlear nerve fibers
↓
Auditory impulses reach brain
Unlike hearing aids, cochlear implants do not amplify sound.
They directly stimulate auditory nerve endings.
| Component | Function |
|---|---|
| External microphone | Receives sound |
| Speech processor | Converts sound into coded signals |
| Transmitting coil | Sends signals across skin |
| Internal receiver-stimulator | Receives signals internally |
| Electrode array | Stimulates cochlear nerve |
Receiver-stimulator
Electrode array
Implanted beneath skin over mastoid.
Receives signals from external transmitter.
Inserted into scala tympani of cochlea.
Electrically stimulates spiral ganglion fibers.
Microphone
Speech processor
Transmitting coil
Battery
Receives environmental sound.
Converts sound into coded electrical signals.
Transmits signals transcutaneously.
Usually through:
Round window
OR
Cochleostomy
Electrode inserted into scala tympani.
Maximum cochlear coverage with minimal trauma.
Mastoidectomy
Posterior tympanotomy
Round window/cochleostomy exposure
Electrode insertion
Device fixation
Programming and adjustment of cochlear implant settings after surgery.
Optimize hearing perception.
Adjust electrical stimulation levels.
Threshold level (T level)
Comfortable loudness level (C level)
Essential for successful hearing rehabilitation.
Specialized therapy teaching child to use hearing for speech and language development.
Listening skills
Speech understanding
Spoken language development
Critical after pediatric cochlear implantation.
Severe to profound bilateral SNHL with poor benefit from hearing aids.
Congenital profound SNHL
Delayed speech due to deafness
Postlingual profound SNHL
Auditory neuropathy spectrum disorder
Ossified cochlea after meningitis
Bilateral severe SNHL
Poor speech discrimination despite hearing aids.
Absent cochlear nerve
Complete cochlear aplasia
Severe medical unfitness
Active middle ear infection
Severe developmental delay
Poor motivation
Psychiatric illness
| Complication | Cause |
|---|---|
| Facial nerve injury | Surgical trauma |
| CSF leak | Cochlear opening |
| Meningitis | Inner ear communication |
| Wound infection | Postoperative infection |
Device failure
Electrode migration
Magnet displacement
Poor speech outcome
Persistent tinnitus
Vertigo
Cochlear implantation in both ears.
Better sound localization
Improved hearing in noise
Better speech perception
Improved binaural hearing
| Type | Meaning |
|---|---|
| Simultaneous | Both ears implanted together |
| Sequential | Second implant later |
| Feature | Hearing Aid | Cochlear Implant |
|---|---|---|
| Mechanism | Amplifies sound | Direct neural stimulation |
| Requires functioning hair cells | Yes | No |
| Indication | Mild–severe HL | Severe/profound SNHL |
| Surgery required | No | Yes |
Electrode inserted into scala tympani.
Main pediatric indication → Congenital profound SNHL.
AVT essential after implantation.
Bilateral implantation improves sound localization.
Cochlear implant bypasses damaged hair cells.
Implantable auditory prosthesis directly stimulating cochlear nuclei in brainstem.
Sound converted into electrical impulses.
Electrodes stimulate cochlear nucleus directly.
| Cochlear Implant | ABI |
|---|---|
| Stimulates cochlear nerve | Stimulates cochlear nucleus |
| Requires intact auditory nerve | Used when auditory nerve absent |
Bilateral vestibular schwannoma in Neurofibromatosis type 2 (NF2)
Cochlear nerve aplasia
Severe cochlear ossification
Failed cochlear implantation
Process of improving communication ability in hearing-impaired individuals.
Improve speech understanding
Improve communication skills
Improve social integration
Improve quality of life
| Method | Purpose |
|---|---|
| Speech therapy | Speech development |
| Lip reading | Visual speech understanding |
| Auditory training | Improve listening skills |
| Counseling | Psychological support |
Training to improve speech and language skills.
Essential in:
Congenital deafness
Pediatric cochlear implant patients
Speech production
Language development
Communication training
Understanding speech by observing lip and facial movements.
Improves communication in hearing-impaired patients.
Not all sounds visible on lips.
Training to recognize and interpret sounds.
Sound awareness
Speech recognition
Auditory memory
Formal auditory training
Informal auditory training
Essential part of rehabilitation.
Education regarding hearing loss
Hearing aid counseling
Family support
Psychological support
Early diagnosis
Hearing amplification
Speech therapy
Parent participation
Educational support
| Topic | Important Point |
|---|---|
| Cochlear implant | Bypasses hair cells |
| ABI | Used when cochlear nerve absent |
| AVT | Essential in implanted children |
| Bilateral implant | Better localization |
| Lip reading | Visual communication aid |
Severe/profound SNHL
↓
Hearing aid trial
↓
Poor benefit
↓
Cochlear implant evaluation
↓
Surgery
↓
Mapping
↓
Auditory verbal therapy
↓
Long-term rehabilitation
Recent advances in audiology aim to:
Improve early diagnosis
Improve hearing rehabilitation
Provide precision medicine
Enhance speech understanding
Improve quality of life
Use of digital technology in hearing assessment and rehabilitation.
Computerized hearing evaluation
Digital signal processing
Advanced hearing aid programming
Data storage and analysis
Better accuracy
Faster testing
Improved customization
Reduced background noise interference
Digital hearing aids
Automated audiometry
Cochlear implant mapping
Tele-audiology
Noise reduction
Directional microphones
Feedback suppression
Frequency shaping
Bluetooth connectivity
Audiometry performed automatically by computer-based systems with minimal examiner involvement.
Automated presentation of tones and recording of patient responses.
Reduced examiner bias
Faster screening
Useful in mass screening programs
School screening
Occupational screening
Telemedicine
Remote hearing assessment
Delivery of audiological services using telecommunication technology.
Remote hearing assessment
Online counseling
Hearing aid programming
Cochlear implant follow-up
Rural healthcare access
Reduced travel burden
Faster specialist consultation
Internet dependence
Technical issues
Limited physical examination
Newborn hearing screening
Remote hearing aid fitting
Cochlear implant mapping
Rehabilitation follow-up
Devices implanted surgically to improve hearing.
| Device | Main Principle |
|---|---|
| Cochlear implant | Direct auditory nerve stimulation |
| BAHA | Bone conduction |
| Middle ear implant | Ossicular stimulation |
| ABI | Cochlear nucleus stimulation |
Better sound quality
Reduced feedback
Improved cosmetic appearance
Combination of:
Acoustic amplification for low frequencies
Electrical stimulation for high frequencies
Residual low-frequency hearing
High-frequency severe SNHL
Better music appreciation
Better speech perception in noise
Preservation of residual hearing
Identifies hereditary hearing loss.
Helps genetic counseling.
| Gene | Associated Hearing Loss |
|---|---|
| GJB2 (Connexin 26) | Nonsyndromic SNHL |
| SLC26A4 | Pendred syndrome |
| MYO7A | Usher syndrome |
Early diagnosis
Family counseling
Prognostic information
Personalized management
Genetic testing in newborns for hereditary hearing loss mutations.
Detects hearing loss before symptoms appear.
Helps early rehabilitation.
Cost
Ethical concerns
Variable gene expression
Stem cells used to regenerate damaged cochlear structures.
Hair cells
Spiral ganglion neurons
Supporting cells
Mostly experimental.
Restoration of hearing
Cochlear repair
Mammalian cochlear hair cells normally do not regenerate.
Regeneration of:
Inner hair cells
Outer hair cells
Supporting cell conversion
Gene activation pathways
Stem cell implantation
NIHL
Ototoxicity
Presbycusis
Introduction or correction of genes responsible for hearing loss.
Restore cochlear function
Prevent hair cell degeneration
Correct genetic defects
Viral vectors
CRISPR gene editing
RNA-based therapy
Congenital deafness
Genetic SNHL
AI identifies hearing loss patterns.
Adaptive sound processing
Personalized fitting
Improved speech enhancement in noise
Automated mapping algorithms
Predicts progression of hearing loss.
Faster diagnosis
Improved accuracy
Personalized rehabilitation
Remote monitoring
AI-based real-time hearing assistance
Smart hearing devices
Predictive hearing conservation systems
| Traditional Audiology | Recent Advances |
|---|---|
| Manual audiometry | Automated audiometry |
| Conventional hearing aids | Digital smart hearing aids |
| Hospital-based care | Tele-audiology |
| Fixed amplification | AI adaptive amplification |
| Limited genetic evaluation | Genetic testing |
| Topic | Important Point |
|---|---|
| Tele-audiology | Remote audiological care |
| Hybrid cochlear implant | Preserves low-frequency hearing |
| Connexin 26 mutation | Common hereditary deafness gene |
| Hair cell regeneration | Experimental future therapy |
| AI audiology | Automated diagnosis & rehabilitation |
Biological restoration of hearing
Fully implantable hearing devices
Smart AI-assisted cochlear implants
Personalized genetic therapies
Nanotechnology-based hearing restoration
Genetic diagnosis
↓
Early screening
↓
Targeted therapy
↓
Hair cell regeneration/gene therapy
↓
Improved auditory rehabilitation
| Property | Definition | Clinical Importance |
|---|---|---|
| Frequency | Number of vibrations/sec | Determines pitch |
| Intensity | Sound energy/unit area | Determines loudness |
| Amplitude | Maximum displacement | Related to intensity |
| Pitch | Perception of frequency | Speech/music recognition |
| Loudness | Perception of intensity | Subjective hearing |
| Timbre | Quality of sound | Sound differentiation |
| Phase | Time relation between waves | Localization |
| Velocity | Speed of sound propagation | Medium dependent |
| Feature | Frequency | Pitch |
|---|---|---|
| Nature | Physical property | Psychological perception |
| Unit | Hertz | No unit |
| Depends on | Vibrations/sec | Brain perception |
| Increase causes | Higher frequency | Higher pitch |
| Feature | Intensity | Loudness |
|---|---|---|
| Nature | Physical | Subjective |
| Unit | dB | No fixed unit |
| Depends on | Sound energy | Brain perception |
| Measured by | Instruments | Human response |
| Feature | Pure Tone | Noise |
|---|---|---|
| Frequencies | Single | Multiple/random |
| Periodicity | Regular | Irregular |
| Use | Audiometry | Masking |
| Example | Tuning fork | Traffic noise |
| Sound Type | Frequency Range |
|---|---|
| Human hearing | 20–20,000 Hz |
| Speech frequencies | 500–4000 Hz |
| Telephone range | 300–3400 Hz |
| Most sensitive range | 1000–4000 Hz |
| Speech Component | Frequency |
|---|---|
| Vowels | Low frequency |
| Consonants | High frequency |
| Important speech range | 500–4000 Hz |
| Device | Frequency Range |
|---|---|
| Telephone | 300–3400 Hz |
| Unit | Meaning |
|---|---|
| Hertz (Hz) | Frequency |
| Bel | Logarithmic intensity unit |
| Decibel (dB) | One-tenth bel |
| Pascal | Sound pressure |
| Component | Effect |
|---|---|
| Mass | Opposes high frequencies |
| Stiffness | Opposes low frequencies |
| Friction | Dissipates sound energy |
| Feature | Endolymph | Perilymph |
|---|---|---|
| Location | Scala media | Scala vestibuli & tympani |
| Potassium | High | Low |
| Sodium | Low | High |
| Potential | +80 mV | Near 0 |
| Produced by | Stria vascularis | Extracellular fluid-like |
| Feature | Inner Hair Cells | Outer Hair Cells |
|---|---|---|
| Rows | 1 | 3 |
| Number | ~3500 | ~12,000 |
| Main role | Sensory transduction | Cochlear amplification |
| Nerve supply | Mainly afferent | Mainly efferent |
| Motility | Absent | Present |
| Damage effect | Major hearing loss | Reduced tuning/sensitivity |
| Potential | Source | Nature | Clinical Use |
|---|---|---|---|
| Endocochlear potential | Stria vascularis | DC | Cochlear ionic balance |
| Cochlear microphonic | Outer hair cells | AC | Hair cell function |
| Summating potential | Hair cells | DC | Meniere disease |
| Action potential | Auditory nerve | Neural response | BERA/ECoG |
| Theory | Main Concept | Limitation |
|---|---|---|
| Helmholtz place theory | Frequency determined by basilar membrane site | Cannot explain low frequencies fully |
| Rutherford frequency theory | Frequency determined by nerve firing rate | Cannot explain high frequencies |
| Volley principle | Groups of neurons encode frequencies | Partial explanation |
| Traveling wave theory | Wave travels along basilar membrane | Most accepted |
| Mechanism | Principle |
|---|---|
| Rate coding | Loudness coded by firing rate |
| Temporal coding | Timing of impulses codes frequency |
| Place coding | Frequency coded by basilar membrane site |
| Feature | Cochlear Lesion | Retrocochlear Lesion |
|---|---|---|
| Recruitment | Present | Absent |
| SISI test | Positive | Negative |
| Tone decay | Minimal | Marked |
| Speech discrimination | Mildly reduced | Markedly reduced |
| BERA | Usually normal IPL | Prolonged IPL |
| Feature | Conductive HL | SNHL |
|---|---|---|
| Site | External/middle ear | Cochlea/nerve |
| Air conduction | Reduced | Reduced |
| Bone conduction | Normal | Reduced |
| Air-bone gap | Present | Absent |
| Rinne | Negative | Positive |
| Weber | To affected ear | To better ear |
| Speech discrimination | Normal | Reduced |
| Recruitment | Absent | Present |
| Feature | Peripheral | Central |
|---|---|---|
| Site | Cochlea/auditory nerve | Brainstem/cortex |
| PTA | Abnormal | May be normal |
| Speech understanding | Reduced | Markedly impaired |
| Localization | Mildly affected | Severely affected |
| Feature | Congenital | Acquired |
|---|---|---|
| Present at birth | Yes | No |
| Causes | Genetic/TORCH | Infection, noise, aging |
| Speech development | Affected early | Depends on onset |
| Rehabilitation | Early intervention needed | Variable |
| Feature | Presbycusis | NIHL |
|---|---|---|
| Cause | Aging | Noise exposure |
| Pattern | Bilateral high-frequency SNHL | 4 kHz notch |
| Progression | Gradual | Exposure related |
| Tinnitus | Common | Common |
| Feature | TTS | PTS |
|---|---|---|
| Reversibility | Reversible | Irreversible |
| Cause | Temporary fatigue | Hair cell destruction |
| Recovery | Hours–days | No recovery |
| Test | Main Principle | Main Use |
|---|---|---|
| Rinne | AC vs BC | CHL vs SNHL |
| Weber | Lateralization | Unilateral HL |
| ABC | Compare BC with examiner | SNHL |
| Schwabach | Duration of BC | CHL/SNHL |
| Bing | Occlusion effect | CHL |
| Gelle | Stapes mobility | Otosclerosis |
| Type | Finding | Condition |
|---|---|---|
| A | Normal peak | Normal |
| As | Shallow peak | Otosclerosis |
| Ad | Deep peak | Ossicular discontinuity |
| B | Flat | OME/perforation |
| C | Negative pressure | ET dysfunction |
| Feature | OAE | BERA |
|---|---|---|
| Site assessed | Outer hair cells | Auditory nerve/brainstem |
| Cooperation needed | No | No |
| Screening use | Excellent | Excellent |
| Retrocochlear lesion | No | Yes |
| Auditory neuropathy | OAE present | BERA absent |
| Feature | Subjective | Objective |
|---|---|---|
| Patient response | Needed | Not needed |
| Example | PTA | BERA |
| Infant use | Difficult | Useful |
| Feature | Screening | Diagnostic |
|---|---|---|
| Purpose | Detect possible HL | Confirm diagnosis |
| Time | Short | Longer |
| Example | OAE | PTA/BERA |
| Test | Principle | Positive In |
|---|---|---|
| SISI | Small increment detection | Cochlear lesion |
| ABLB | Loudness balancing | Cochlear lesion |
| Metz | Reflex threshold | Recruitment |
| Test | Principle |
|---|---|
| Stenger | Stenger phenomenon |
| Lombard | Voice reflex in noise |
| Chimani-Moos | Occlusion effect |
| Delayed auditory feedback | Speech disruption |
| Age | Preferred Test |
|---|---|
| 0–6 months | BOA |
| 6 months–2 years | VRA/COR |
| 2–5 years | Play audiometry |
| >5 years | PTA |
| Baby Type | Preferred Screening |
|---|---|
| Normal newborn | OAE |
| High-risk infant | BERA/AABR |
| Risk Factor | Importance |
|---|---|
| NICU stay | Auditory injury risk |
| TORCH infection | Congenital SNHL |
| Hyperbilirubinemia | Auditory neuropathy |
| Family history | Genetic deafness |
| Craniofacial anomaly | Structural defects |
| Type | Main Feature |
|---|---|
| Body worn | Large external device |
| BTE | Behind ear |
| ITE | Entirely in ear |
| ITC | In canal |
| CIC | Completely in canal |
| RIC | Receiver in canal |
| Feature | Analog | Digital |
|---|---|---|
| Signal processing | Analog | Digital |
| Noise reduction | Poor | Better |
| Programming | Limited | Advanced |
| Speech clarity | Less | Better |
| Feature | Hearing Aid | BAHA | Cochlear Implant |
|---|---|---|---|
| Mechanism | Amplifies sound | Bone conduction | Direct nerve stimulation |
| Needs intact cochlea | Yes | Yes | Auditory nerve needed |
| Best for | Mild–severe HL | Conductive HL | Profound SNHL |
| Surgery | No | Yes | Yes |
Sound wave
↓
Tympanic membrane vibration
↓
Ossicular movement
↓
Stapes movement at oval window
↓
Perilymph movement
↓
Basilar membrane vibration
↓
Hair cell stimulation
↓
Auditory nerve impulse
↓
Auditory cortex
External ear
↓
Tympanic membrane
↓
Malleus
↓
Incus
↓
Stapes
↓
Oval window
↓
Cochlea
Hair cells
↓
Spiral ganglion
↓
Cochlear nerve
↓
Cochlear nuclei
↓
Superior olivary complex
↓
Lateral lemniscus
↓
Inferior colliculus
↓
Medial geniculate body
↓
Auditory cortex
Hearing loss
↓
Tuning fork tests
↓
Air-bone gap present
→ Conductive HL
No air-bone gap
→ SNHL
Speech discrimination poor
→ Retrocochlear suspicion
Rinne negative
→ Conductive HL
Weber to affected ear
→ Conductive HL
Weber to better ear
→ SNHL
Air-bone gap present
→ Conductive HL
Both AC & BC reduced without gap
→ SNHL
Both reduced + gap
→ Mixed HL
Type A
→ Normal
Type As
→ Otosclerosis
Type Ad
→ Ossicular discontinuity
Type B
→ OME/perforation
Type C
→ ET dysfunction
Tinnitus
↓
Pulsatile?
→ Vascular evaluation
Non-pulsatile
↓
Audiometry
↓
Unilateral SNHL
→ MRI for acoustic neuroma
Newborn
↓
OAE screening
↓
Pass → Routine follow-up
Refer
↓
BERA
↓
Diagnosis
↓
Early rehabilitation
All newborns
↓
OAE
↓
Pass → Normal follow-up
Refer
↓
Repeat OAE/BERA
↓
Confirmed hearing loss
↓
Intervention before 6 months
Severe/profound SNHL
↓
Hearing aid trial
↓
Poor benefit
↓
Audiological evaluation
↓
Imaging
↓
Cochlear implantation
Baseline audiometry/OAE
↓
Start ototoxic drug
↓
Serial monitoring
↓
Threshold shift detected
↓
Dose adjustment/change drug
Diagnosis of hearing loss
↓
Amplification assessment
↓
Hearing aid/cochlear implant
↓
Speech therapy
↓
Auditory training
↓
Long-term follow-up
Longitudinal wave showing:
Compression
Rarefaction
Wavelength
Amplitude
Comparison of:
High vs low frequency
High vs low amplitude
Resonance phenomenon in external auditory canal and middle ear.
Fundamental frequency with harmonic overtones.
Audiogram-shaped speech frequency distribution diagram.
Fletcher-Munson curves demonstrating loudness perception at different frequencies.
Detailed labeled diagram:
Inner hair cells
Outer hair cells
Pillar cells
Tectorial membrane
Scala vestibuli
Scala media
Scala tympani
Reissner membrane
Basilar membrane
Base vs apex comparison and frequency mapping.
Inner vs outer hair cell structure.
Stereocilia tip link mechanism.
Wave propagation along basilar membrane.
High-frequency base vs low-frequency apex.
Endolymph potassium circulation pathway.
Histological and functional diagram.
Complete ascending auditory pathway.
Reflex pathway involving stapedius muscle.
Components and setup.
Normal and pathological audiograms.
Instrument setup and components.
Jerger types:
A
As
Ad
B
C
Probe placement and recording mechanism.
Electrode placement and recording system.
Wave I–V generators and latencies.
Different tracing patterns for cochlear and retrocochlear lesions.
Demonstration of malingering detection.
Comparison of:
BTE
ITE
ITC
CIC
RIC
Bone conduction pathway to cochlea.
External and internal device parts.
Scala tympani electrode insertion and cochlear mapping.
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