The eardrum vibrations caused by sound waves move the chain of tiny bones (the ossicles – malleus, incus and stapes) in the middle ear transferring the sound vibrations into the cochlea of the inner ear. This is where the streams of nerve impulses are converted into meaningful sound.
Parts of ear:
Outer Ear :
Middle Ear: Converts sound waves in to vibrations.
Inner Ear (Cochlea): converts vibrations into electrical impulse. Theses electrical impulse travel to brain via nerve of hearing (Cochlear nerve)
What is cause of Hearing Loss in children?
In children hearing loss can be congenital (from birth) or acquired (after birth). Acquired can be due to various infections or trauma, etc.
Hearing loss can also be classified as per language development as follows
Pre-lingual –hearing loss developed before child could start speaking, it can be either congenital (from birth) or acquired (after birth).
Post-lingual – hearing loss developed after child started speaking. It means it is acquired.
Cause of hearing loss is any defect in the transmission of sound through the ear. It can be
Conductive – Caused by defect in middle or external part of ear. It can usually be treated by some medications. Less frequently a surgery is required to correct this type of hearing loss
Sensori-neural – Caused by defect in nerve of hearing or cochlea. Mild to moderate hearing loss can be treated by hearing aid whereas severe to profound hearing loss requires Cochlear Implant surgery
Burden of Hearing loss?
In US Significant bilateral hearing loss is present in ~1 to 3 per 1000newborn infants in the well-baby nursery population, and in ~2to 4 per 100 infants in the intensive care unit population.
In India, 63 million people (6.3%) suffer from significant auditory loss. Four in every 1000 children suffer from severe to profound hearing loss. The estimated prevalence of childhood onset deafness to be 2%
How to assess Hearing loss in new born and small children?
Detection of infant hearingloss requires universal screening of all infants. Screening byhigh-risk registry alone (eg, family history of deafness) canonly identify ~50% of newborns with significant congenital hearingloss. Reliance on physician observationand/or parental recognition has not been successful in the pastin detecting significant hearing loss especially in the first year of life.
Tests for screeninginclude otoacoustic emissions (OAE) and auditory brainstemresponse (ABR / BERA). Both testare noninvasive, quick, and easy to perform, althougheach assesses hearing differently. Aim is to initiate necessary interventionby 6 months of age.
What is a Cochlear implantation?
A cochlear implant is an electronic medical device that replaces the function of the defective inner ear. Unlike hearing aids, which make sounds louder, cochlear implants do the work of damaged parts of the inner ear (cochlea) to send sound signals to the brain.
Most important thing is early diagnosis. Management of deaf and mute child should be started as early as possible. Success of cochlear implant is more if it is done by the age of 3years. Success rate decreases with advancement of age of child.