Hearing loss

Background of hearing loss

Type Clinical features 
Ear anatomy  
    • Auricle 
      • Senses incoming sound waves and transmits to external auditory canal 
    • External auditory canal (EAC) 
    • Tympanic membrane (TM) 
      • Sound waves vibrate against TM to move ossicles 
    • Ossicles (Stapes, Incus, Malleus) 
      • Push inner ear fluid around cochlea 
    • Middle ear canal 
    • Cochlea 
    • Semicircular canals 
    • Internal auditory canal 
      • Transmits sound via cochlear (auditory) nerve to brain for sound perception 
Classification 
  • Sensorineural hearing loss (SNHL) 
    • Defect is nerve conduction of perceived sound 
    • Involves inner ear, cochlea, or auditory nerve 
  • Conductive hearing loss (CHL) 
    • Defect in conduction of sound from outer ear to inner ear 
  • Mixed 
    • Combination of conductive and sensorineural hearing loss 
  • Sudden sensorineural hearing loss (SSNHL) 
    • Decreased hearing > 30 dB affecting > 3 sound frequencies within 72 hours or less 
    • Usually associated with tinnitus, ear fullness, and vertigo 
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