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Distortion of Sounds That Impairs the Understanding of Words
Effect of a Noisy Environment Patient's Own Voice
Usual Age of Onset
Ear Canal and Drum
Hearing may seem to improve.
Tends to be soft: the patient's voice is conducted through bone to a normal inner ear and cochlear nerve.
Most often in childhood and young adulthood, up to age 40
An abnormality is usually visible, except in otosclerosis.
Often present as the upper tones of words are disproportionately lost
Hearing typically worsens.
May be loud: the patient has trouble hearing his or her own voice.
Most often in the middle or later years. The problem is not visible.
The sound lateralizes to the good ear. The impaired inner ear or cochlear nerve is less able to transmit impulses no matter how the sound reaches the cochlea. The sound is therefore heard in the better ear.
Air conduction lasts longer than bone conduction (AC > BC). The inner ear or cochlear nerve is less able to transmit impulses regardless of how the vibrations reach the cochlea. The normal pattern prevails.
Sustained exposure to loud noise, drugs, infections of the inner ear, trauma, tumors, congenital and hereditary disorders, and aging (presbycusis)
Bone conduction lasts longer than or is equal to air conduction (BC > AC or BC = AC). While air conduction through the external or middle ear is impaired, vibrations through bone bypass the problem to reach the cochlea.
Causes Include' Obstruction of the ear canal, otitis media, a perforated or relatively immobilized eardrum, and otosclerosis (a fixation of the ossicles by bony overgrowth)
The sound lateralizes to the impaired ear. Because this ear is not distracted by room noise, it can detect the tuning fork's vibrations better than normal. (Test yourself while plugging one ear with your finger.) This lateralization disappears in an absolutely quiet room.
Further evaluation is done by audiometry and other specialized procedures.
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