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The
ear
The ear consists of three
parts: the outer ear, middle ear and inner ear.
The outer ear is the visible part of the ear
on either side of the head and includes the ear canals that go
into the head. The fleshy parts of the outer ear act as
"collectors" of sound waves, which then travel down the ear
canal to the eardrum. This is a membrane of tissue that
separates the outer ear from the middle ear.
The sound waves cause the eardrum to vibrate.
This vibration is passed on to the middle ear, which consists
of three small bones called the "ossicles", which amplify and
conduct the vibrations of the eardrum to the inner
ear.
The inner ear consists of an organ called the
cochlea, which is shaped like a snail's shell. The cochlea
contains tiny cells called hair cells which move in response
to the vibrations passed from the ossicles. The movement of
these hair cells generates an electrical signal that is
transmitted to the brain through the auditory
nerve.
Three basic
types of hearing loss: Conductive hearing
loss, Sensorineural
hearing loss and Mixed hearing
loss.
Conductive Loss
This type
of hearing loss occurs when sound is not conducted efficiently
through the outer ear canal to the eardrum and from
eardrum to the tiny bones called ossicles and from the
ossicles to the inner ear. This type of hearing loss
usually involves a reduction in sound
level alongwith the ability to hear faint sounds. It
can often be medically or surgically treated.
Causes of Conductive hearing
loss:
- Due to
accumulation of fluid in the middle ear from colds,
allergies (Serous Otitis Media-S.O.M), eustachian tube
dysfunction, ear infection called otitis media,
perforated eardrum, benign tumors .
- Due to
presence of a foreign body
- Due to
Impacted earwax (cerumen)
- Any kind
of infections in the ear canal.
- Physical disorder of the outer ear,
ear canal or middle ear
- Otosclerosis, a condition in
which the ossicles of the middle ear become immobile because
of growth of the surrounding bone
- Rarely, rheumatoid arthritis
affects the joints between the ossicles.
Sensorineural Loss
This type
of hearing loss occurs when there is problem to the inner ear
called cochlea or to the nerve pathways from the inner ear
called retrocochlear to the brain. It cannot be medically or
surgically corrected. It is a permanent kind of hearing
loss.
It
also involves a reduction in sound level or ability to
hear faint sounds and also affects speech
understanding or ability to hear clear speech.
Causes of Sensorineural hearing
loss:
Due to diseases like maleria, meningitis, mumps, viral
fever
Due to birth injury, brain trauma or any kind of ear
trauma
Taking any kind of toxic medinine
Due to heavy noise exposure
Age-related hearing loss - the decline in hearing that
many people experience as they get older
Ménière's disease (abnormal pressure in the inner ear)
Acoustic neuroma, a benign (non-cancerous) tumour
affecting the auditory nerve
Multiple sclerosis
Tumors in the inner ear
It is a
combination of conductive and sensorineural hearing loss.
Whenever damage in the outer or middle ear alongwith the
inner ear or auditory nerve cause simultaneously then
this kind of hearing loss is occured .
Causes of
Sensorineural hearing loss:
Both the causes involved in conductive and
sensorineural hearing loss are repponsible for this kind of
hearing loss.
Hearing
tests
An audiometer produces sounds of
different volumes and pitch (frequencies). During testing, you
are asked to indicate, usually by pushing a button, when you
hear a sound in the headphones. The level at which a person
cannot hear a sound of a certain frequency, is known as their
threshold.
Hearing loss is measured in
decibels hearing level (dBHL). A person who can hear sounds
across a range of frequencies at 0 to 20 dB is considered to
have normal hearing. The thresholds for the different types of
hearing loss are as follows:
Degree of Hearing Loss
It
refers to the severity of the loss. There are six
broad categories that are typically used to define the degree.
The degrees are representative of the patient's thresholds or
the softest intensity that sound is perceived by the patient:
Normal
range or no impairment = 0 dB to 25 dB
Mild loss
= 25 dB to 40 dB
Moderate
loss = 40 dB to 55 dB
Moderately Severe Loss= 56 dB to 70 dB
Severe
loss = 71 dB to 90 dB
Profound
loss = 91 dB or more
Pattern of Hearing Loss
= High Frequency Hering Loss - refers to the hearing loss
that affects more in high frequency .Its configuration
would show good hearing in the low frequencies and poor
hearing in the high frequencies.
= Low
Frequency Hearing Loss - refers to the hearing loss that
affects more in low frequency. The configuration shows poorer
hearing for low tones and better hearing for high
tones.
= Flat Type
- refers the same amount of hearing problem in low and high
frequencies.
= Bilateral
Hearing Loss - means both ears are affected equally or
unequally.
=Unilateral
Hearing Loss - - means only one ear is affected. Another ear
shows normal hearing thresholds.
=Symmetrical Hearing Loss - means that the degree and
configuration of hearing loss are same in each ear.
=
Asymmetrical Hearing Loss - means the degree and / or
configuration of hte loss is different for each
ear.
=Progressive Hearing Loss - means the loss getting
worse over time to time.
=Sudden
Hearing Loss - means acute or rapid onset and therfore occurs
quickly.
=
Fluctuating Hearing Loss - sometimes getting better and
in other time getting worse. In Conductive and in
Meniere's disease this type of hearing loss are the best
example. |
