Hearing Impairment

Source – Web Health Centre

Hearing Impairment

One survey puts the number of hearing Impaired in India as 4.482 million people (Source: Javed Abidi, Secretary-General, Disabled Peoples’ International in India). (Other sources quote many times this figure.)

Even assuming there are close to five million people with some level of speech/hearing impairment, we find the coping mechanism woefully inadequate. There are several barriers to making the hearing impaired self sufficient. Social attitudes, gender bias, rural urban divide, lack of adequate facilities for schooling and difficulty in integration into society. The cost and effort required for basic healthcare for hearing impaired is also high.

In the face of inadequate facilities, lack of proper guidance, lack of access to the best available care the family has to be highly motivated in helping the hearing impaired. Improved technical devices such as digital hearing aids and cochlear implants as well as new methods of audiometric evaluation are playing a positive role in the rehabilitation of the deaf. Therapy today is oriented towards early screening and auditory training in an attempt at closing the gap between the hearing impaired and normal people. Despite the odds, it is possible to give the hearing impaired a chance to cope with their immediate environment. Awareness is a key factor in the process.

This section hopes to provide information on the possible causes, current treatment options and facilities available in India for the Hearing Impaired.

The Ear and Hearing

The ear or the hearing apparatus in the human being consists of three distinct regions. They are:

The Outer Ear: This consists of the pinna or the “ear” that we are able to see on the sides of our head . This question-mark shaped organ made of soft tissue collects sound vibration from the surroundings.

These sound waves are ferried through the ear canal which also forms part of the outer ear. The ear canal contains glands that secrete wax. The walls of the ear canal are lined with hair that prevent foreign bodies entering the ear. The ear canal ends at the tympanum or eardrum.

Functions: It protects the delicate inner parts of the hearing mechanism. It collects and funnels sound waves into the ear. It helps in the judgment of direction and distance of sounds.
The Middle Ear: The eardrum and the three tiny bones or ossicles beyond it form the middle ear. This is an air filled chamber. The ossicles function like a hammer(malleus), anvil (incus) and stirrup (stapes) in co ordination. The stapes is attached to a foot plate which is in direct contact with the fluid of the inner ear.When airwaves hit the ear drum the ossicles move, corresponding to the kind of vibration received and this pattern is received by the footplate. The footplate communicates the pattern to the inner ear.

Functions:It transmits and amplifies sound waves from tympanic membrane to the stapes footplate converting energy from air medium to a fluid medium of the inner ear.
The Inner Ear: This is a fluid filled labyrinth consisting of the vestibule, the cochlea and the semicircular canals. Of these the snail shaped cochlea is the part concerned with hearing.

The cochlea is a bony structure filled with fluid. There are sensory receptors inside the cochlea which holds the hair cells, the nerve receptors for hearing. The mechanical energy of the middle ear hits the cochlea and moves the fluid in it. This stimulates the hair cells. Signals from these hair cells are translated into nerve impulses. The nerve impulses are transmitted to the brain by the cochlear portion of the acoustic nerve.

From the ear the cochlear nerve carries the auditory signals to the brain. The part of the brain that receives these signals is called the auditory cortex. From each ear auditory signals are conveyed to both sides(hemispheres of the brain). This way what is heard by the left ear is conveyed to the right side of the brain and also to the left side.

We make sense of what we hear because the Central auditory complex in the brain process the impulses conveyed to it. It helps us to understand the pattern of the sounds, place the sound in time and place, adjust our hearing

Causes and Types of Hearing Loss

Congenital Hearing Loss
Acquired Hearing Loss
Sensorineural Hearing Loss ( Cannot be corrected)
Conductive Hearing Loss ( Can be corrected)

The ear and the hearing mechanism in the human being are made up of a number of tiny, specialised parts and millions of nerve cells. Malformation, damage or reduction of any of these, owing to various factors, causes hearing impairment.

Congenital Factors:

Some types of hearing loss are present from birth. Several factors may be responsible for this.

Genetic: The most common congenital factor is genetic. A child with one or both parents with hearing impairment can inherit the dominant gene for hearing loss. It is possible to inherit hearing loss even if a grandparent is deaf.

Infections: Diseases like jaundice, rubella, pox in the prenatal, peri natal and post natal periods can affect hearing.

Problems relating to birth: Prematurity or anoxia ( “blue babies”/lack of oxygen at the time of birth).

Malformation: A part of the hearing mechanism may be malformed.

Mother’s condition during pregnancy: Some conditions affecting the mother, such as toxemia, syphilis, Rh incompatibility, or diabetes can affect hearing of the foetus.

Acquired Hearing Loss

Hearing loss may be acquired after birth, at any age. These may be reversible or permanent. Some factors that produce hearing loss are:

Infections: Infections in the ear can cause hearing loss.

Viral or bacterial infections like Encephalitis, Chicken pox, Measles, Mumps, Meningitis, Syphilis etc may also cause hearing loss in some people.

Trauma: Head injury, concussion or trauma that affects the hearing mechanism. Some times water sports can, due to pressure differences, rupture parts in the ear, leading to hearing loss.

Medication: Medicines called “ Ototoxic” drugs are capable of causing reversible or permanent hearing loss in some people. Salicylates ( Aspirin containing medicines), Non steroid anti inflammatory drugs, some Antibiotics ( Aminoglycosides, Erythromycin, Vancomycin), Diuretics, Chemotherapy agents, Quinine are some Ototoxic drugs.

Noise: Continued exposure to noisy environments like factories or blast sites can affect hearing. At first the high frequency hearing is affected. If exposure continues, hearing loss is progressive.

Age: Some people experience hearing loss as they age. This condition is called Presbycusis.

Others: There are some rare conditions like tumour in the Acoustic nerve or Otosclerosis ( hardening of bones/or parts of the hearing mechanism). Hearing impairment can also occur abruptly, without any apparent cause!

Conductive Hearing Loss ( Can Be Reversed)

External or middle ear problems, which are often mechanical in nature cause hearing loss. This can usually be corrected by medication or surgery. Middle Ear Infections (Otitis Medea) are a common cause.

Ear discharge or accumulation of ear wax can also cause hearing loss.

Absence or malformation of parts of the external or middle ear can cause conductive hearing loss.

Sensorineural Hearing Loss (Cannot Be Reversed)

Problems in the inner ear involving the cochlea, the hair cells or nerve cells cause sensorineural hearing loss. This type of hearing loss is irreversible. This can be congenital or acquired.

Neither medication nor surgery can make the patient regain the ability to hear. However, hearing devices and implants are used, along with auditory training, to help these patients hear.