Types of Hearing Impairment

Conductive Hearing Loss:

Conductive hearing loss results from defects in the outer or middle ear. The sound is not conducted efficiently to the inner ear. All sounds heard thus become weak and/or muffled. Usually such individuals speak softly irrespective of the surrounding environmental noise.

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Conditions that cause conductive hearing loss are:

  • Wax in the ear canal.
  • Diseases of the outer and middle ear associated with symptoms like ear ache and ear discharge.
  • Congenital defects in the outer or middle ear – defect and damage to the outer or middle ear.
  • Upper respiratory tract infections.
  • Neglect of care of ears and oral cavity (mouth).

Sensorineural Hearing Loss:

Sensorineural hearing loss is caused due to damage or disease of the inner ear or auditory nerve. It could also result as an after effect of infectious diseases like measles, mumps, meningitis and T.B.

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Some conditions that may cause congenital sensorineural hearing loss are:

  • Hereditary childhood deafness
  • Rh incompatibility
  • Premature birth – birth before due time
  • Birth Asphyxia (lack of oxygen supply to the new born due to inability to breathe normally resulting in blueness of baby due to various reasons).
  • Viral infections in pregnancy
  • Exposure to X–rays in the first trimester or pregnancy – taking X–ray within the first three months
  • Harmful drugs of mycin variety e.g. streptomycin
  • Acoustic neuroma (Tumor of the auditory nerve)

Mixed Hearing Loss:

Mixed hearing loss is the combination of conductive and sensorineural hearing loss. One of the main causes of this type of loss is the long standing ear infection known as Chronic Suppurative Otitis Media (CSOM). In CSOM, ear discharge in the form of pus, blood or clear water is seen. This starts with conductive loss yielding to sensorineural impairment, if not treated immediately and regularly.

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Central Hearing Loss:

Central hearing loss is due to a damage, malformation or infections of the neural pathways and the hearing centres in the brain. The child may hear but has difficulty in understanding what he hears. Some of the children classified as learning disabled or slow learners may have this type of hearing loss.

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Functional Hearing Loss:

Functional hearing loss is due to some psychogenic condition or maybe due to deliberate exaggeration of hearing thresholds for personal gains.

Categories of Hearing Impairment/Disability

Hearing impairment may be of various degrees (Ref.column 2 below). The degree of hearing impairment (in dBHL) as given in column 3 below is calculated by averaging the hearing thresholds at 500 Hz, 1 khz & 2 khz obtained from pure tone audiometry. Speech recognition score (Ref. Column 4 below) is obtained by administering Speech Audiometry. Hearing disability (Ref. Column 5 below) is calculated by the prescribed formula and is in percentage. The nature and quantum of benefits/facilities provided by the Government is based on the degree and percentage of disability.

Various Impairment

Catetory Degree of Impairment dB Level (HL) Speech Recognition Hearing in %
I Mild Hearing Impairment 26 to 40 dB in better ear 80 to 100% in better ear Less
II (a) Moderate Hearing Impairment 41 to 60 dB in better ear 50 to 80% in better ear 40%
II (b) Severe Hearing Impairment 60 to 70 dB in better ear 40 to 50% in better ear 51%
III (a) Profound Hearing Impairment 71 to 90 dB in better ear Less than 40% in better ear 71%
III (b) Total deafness 91 dB and above in better ear Very poor discrimination 100%
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