It is not surprising that things can go wrong in the elaborate
auditory system, and these problems can result in a reduced ability
to hear.
Hearing losses are grouped into four categories - central / retro-cochlear,
conductive, sensorineural and mixed.
Central or Retro-cochlear Loss
This least common form of hearing impairment occurs when there
is a problem in the central auditory system. Although the outer,
middle and inner parts of the ear deliver sound signals, these
signals are unable to be processed by the brain. Amplification
does not help this type of dysfunction.
Conductive Loss
More frequent than central hearing loss, conductive hearing impairment
results from malfunction of the outer and/or middle ear. Conductive
losses can be caused by something as simple as impacted earwax,
or something as serious as middle ear infection, eardrum perforation
or disarticulation of the ossicles.
Many of these problems can be medically or surgically treated
and hearing health care professionals are obligated to report
such conditions to clients' physicians. When treated in time,
some conductive losses may not require amplification. Other conductive
losses are untreatable and in these cases hearing instruments
are an important consideration.
 Sensorineural Hearing Loss
Sensorineural hearing loss is by far the most common type of impairment.
It is usually the result of cochlear haircell damage; the outer
and middle ear conduct sound to the inner ear, but some haircells
are unable to "trigger" and therefore cannot send signals to the
central auditory system.
Because the cochlea is tiny and the haircells themselves are
microscopic, no medical procedure can "fix" sensorineural hearing
loss. The cochlea lies deep within the skull's temporal bone and
cannot be reached without ruining all the haircells. Unlike conductive
hearing losses, sensorineural hearing loss is considered permanent
and irreversible.
Fortunately, sensorineural loss can be aided with amplification,
which makes sounds louder so that remaining healthy haircells
can respond and trigger nerve impulses.
Although hearing instruments help people with hearing loss, there
is nothing that can restore sensorineural impairment and no hearing
instrument can compensate for damaged hearing at every pitch.
Nonetheless, hard of hearing people are able to enjoy improved
communication as a result of using hearing instruments.
Several things can cause sensorineural hearing loss, such as:
- hereditary predisposition
- prenatal, perinatal or congenital factors (i.e.: thalidomide)
- disease
- prolonged exposure to excessive noise
- ototoxic medication
- chemotherapy
- age
Age is the most prevalent cause of hearing impairment. Presbycusis
is the term given to age-induced hearing loss which occurs as
part of the natural deterioration of the human body as it grows
older.
Mixed Loss
Mixed hearing loss is a condition in which both conductive and
sensorineural hearing loss is present.
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