Deafness
Impaired perception of acoustic signals.
Diagnosis
Often the diagnosis is obvious or can be confirmed by a simple hearing test. More subtle hearing impairments can be measured audiometrically, which also allows to distinguish different types of deafness. Objective audiometry, which uses EEG signals to confirm acoustic signal perception, is available for small children, mentally disabled, and notorious liars.
Pathogenesis
Deafness may be hereditary or acquired. The latter is mostly due to a chronic noise trauma and called loud noise deafness. Congenital deafness, when results from malformation, often exists right from birth. However, hereditary deafness may also develop with age. Then it is often due to disturbed metabolism or regeneration and difficult to distinguish from acquired forms.
Classification
According to the site of damage deafness may be divided into conductive, sensorineural, and mixed. In conductive deafness the conduction of sonic waves onto the cochlea is blocked. Sensorineural deafness is either due to a cochlear or retrocochlear lesion. We further distinguish symmetrical and asymmetrical hearing loss. Audiometric measurement allows to distinguish high frequency deafness.
