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Hearing loss

   Types, Degree and Pattern of Hearing Loss:

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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
  • Meniere's disease (abnormal pressure in the inner ear)
  • Acoustic neuroma, a benign (non-cancerous) tumour affecting the auditory nerve
  • Multiple sclerosis
  • 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.