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