All organs in the human body perform various functions in coordination with each other which helps people in doing their day-to-day activities normally without any problem. But if any one of these organs fails to work properly, the whole system gets disrupted and causes difficulties in the functioning of the body. This problem in body function is called as impairment. Often, impairment is replaced with the term disability when one wants to refer to the limitation in activity caused due to the physiological or psychological abnormality (Impairment, Disability and Handicap, n.d.). In this paper, the term impairment will be used only to denote the health condition in medical terms and not the social situations which show the inability of the individual (especially children) to perform his/her responsibilities.
Immanuel Kant proposed that our knowledge of the outside world depends on our modes of perception. Exteroceptive senses are senses that perceive the body's own position, motion, and state. The human body consists traditionally of 5 external senses namely: sight, hearing, touch, smell and taste. These senses work with the help of specialised cellular structures which are eyes, ears, tongue, nose and skin. The sensing is integrated into the nervous system and hence linked to the brain. This paper discusses the various aspects of hearing impairment and its effect on the development of such children.
The ear(s) is responsible for sound perception over a range of frequencies from 20-20,000 Hertz. It helps in differentiating between speech, music and environmental sounds including traffic, chirping of birds, rain, thundering, etc. It is also responsible for developing the sense of balance and spatial orientation (Anatomy and Structure, n.d.). One of the most important effects it has on the speech and language development. This will be discussed later. Hearing impairment affects the development of vocabulary and comprehension of children, consequently affecting their academic achievement. It also causes their isolation in society as they are not able to understand others’ speech or express their own thoughts orally. In the following sections, the definition of hearing impairment, causes of hearing impairment in children have been presented along with its various types.
1. Definition of Hearing Impairment
The World Health Organisation (WHO, 2014) defines hearing impairment as “ hearing loss greater than 40 dB in the better hearing ear in adults and a hearing loss greater than 30 dB in the better hearing ear in children.”
According to The Rehabilitation Council of India Act, 1992, “hearing handicap means deafness with hearing impairment of 70 decibels and above, in the better ear or total loss of hearing in both ears” (Clause 2 (1)(d)).
The legal definition of hearing impairment in India was given by The Persons with Disability Act, 1995 which is as follows: "Hearing impairment means loss of sixty decibels or more in the better ear in the conversational range of frequencies” (Clause 2 (l)).
From the above definitions, it is evident that hearing impairment is defined in terms of the degree of hearing loss and it differs from one definition to another although the reason for these differences is not clear.
Degree of hearing loss
The degree of hearing loss is determined by looking at the range of decibels an individual is able to hear. This is done by using a formal hearing test known as audiogram. This degree is generally classified in seven categories as per Goodman’s (1965) classification and an additional category — slight hearing loss is added between the normal hearing and mild hearing loss especially when assessing the hearing sensitivity of young children (RCI, n.d.).
Table 1: Classification of Severity of Hearing Impairment
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Degree of Hearing Loss
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Hearing Loss Range (db HL)
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Normal
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-10 to 15
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Slight
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16 to 25
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Mild
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26 to 45
|
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Moderate
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46 to 55
|
The following section describes the various causes leading to hearing impairment.
2. Causes of Hearing Impairment
The causes of hearing impairment can be broadly divided into two categories:
2.1. Congenital causes
2.2. Acquired causes
2.1. Congenital causes
Congenital deafness is the loss of hearing present from birth and is mostly caused due to genetic factors. This can again be classified into two types:
2.1.1. Autosomal recessive hearing loss: In this, both parents carry the recessive gene and pass it along to the child. The parents might not have the impairment but the child inherits it. This type of inheritance pattern accounts for about 70% of all genetic hearing loss.
2.1.2. Autosomal dominant hearing loss: An abnormal gene from one parent causes hearing loss even though the matching gene from the other parent is normal. The parent who is carrying the dominant gene may or may not have hearing loss. The autosomal dominant pattern accounts for 15% of all genetic hearing loss cases.
Down Syndrome and Treacher Collins Syndrome are the genetic syndromes which have hearing loss as one of their symptoms (Hearing loss, n.d.).
Down Syndrome (also known as Trisomy 21 or Trisomy G) is a chromosomal disorder caused by an extra 21st chromosome. People with Down Syndrome are at an increased risk of congenital heart defects, organic disorders and hearing loss. Chronic ear infections such as otitis media with effusion (OME) are the most common cause of hearing loss in children with Down Syndrome. Auditory system malformations and neural transmission problems can also cause hearing loss. The degree of hearing loss in children with Down Syndrome varies, but even mild cases can have serious consequences for their speech perception, language acquisition, academic achievement and social interaction.
Treacher Collins Syndrome, also known as Franceschetti syndrome or mandibulofacial dysostosis, is a genetic disorder. Treacher Collins is often accompanied by chronic respiratory insufficiency, sleeping apnea and a conductive hearing loss due to outer and middle ear malformations. The hearing loss is generally bilateral (occurring in both ears) with a conductive loss of about 50-70 decibels. Even in cases with normal and open external auditory canals, the ossicular chain (bones in the middle ear which help amplify sound) is often malformed. Treacher Collins is rare, occurring approximately once in every 10,000 births.
2.1.3. Non-genetic factors: Infections during pregnancy or at the time of labour can also lead to hearing loss. Following is a list of factors causing non-genetic hearing loss in children:
- maternal rubella, syphilis or certain other infections during pregnancy
- inappropriate use of ototoxic drugs (such as aminoglycosides, cytotoxic drugs, antimalarial drugs and diuretics) during pregnancy
- drugs and alcohol consumed by the mother during pregnancy
- maternal diabetes
- low birth weight
- birth asphyxia (a lack of oxygen at the time of birth)
- severe jaundice in the neonatal period, which can damage the hearing nerve in a newborn infant
- prematurity
2.2. Acquired causes
- Meningitis is a viral or bacterial infection that causes inflammation and swelling of the membranes covering the brain and spinal cord. The most common symptoms of meningitis are headache and neck stiffness associated with fever, confusion or altered consciousness, vomiting, and an inability to tolerate light (photophobia) or loud noises (phonophobia). Hearing loss or deafness are amongst it possible serious complications.
- Chronic Otitis Media: Otitis media (OM) is a middle ear infection which mostly affects children and is the most common childhood disease in the world. The stages of otitis media are diagnosed according to their severity: acute otitis media (AOM); otitis media with effusion (OME); chronic otitis media (COM); and chronic suppurative otitis media (CSOM). Periods of conductive hearing loss from otitis media may have a detrimental effect on speech development in children and are linked to educational problems, attention disorders and problems with social adaptation.
- External Otitis (Otitis Externa): External otitis is an inflammation of the external ear and/or ear canal. Its most commonly caused by an active bacterial or fungal infection. External otitis is also referred to as ‘swimmer's ear’, as it’s often a bacterial infection caused by excessive water exposure. In most cases, the ear canal tissue swells and may become painful and/or tender to touch.
- Ototoxic medicines damage the ear and are a common cause of hearing loss, especially children who may need medicine on a regular basis. The first symptoms usually are ringing in the ears (tinnitus) and vertigo. Hearing loss caused by an ototoxic medicine tends to develop quickly but hearing may return to normal once the medicine is ceased. However some medicines can cause permanent damage to the inner ear. Commonly used medicines that may cause hearing loss include: large doses of aspirin; non-steroidal anti-inflammatory drugs; some antibiotics; loop diuretics used to treat high blood pressure and heart failure; and medicines used to treat cancer in children.
- Trauma: Acoustic trauma is injury to the inner ear’s hearing mechanisms from very loud noise. This may include an explosion near the ear, gunshots or loud music or machinery over a long period of time. Symptoms include hearing loss, which is usually partial and involving high-pitched sounds, and ringing in the ear or tinnitus. Hearing loss caused by acoustic trauma may worsen over time.
- Atresia/microtia: Atresia is the absence of an external ear canal, and is often accompanied by microtia, where the external ear develops abnormally. The malformations of atresia/microtia can cause a conductive hearing loss. Atresia/microtia usually happens in isolation, but it can also occur as a symptom of syndromes such as Goldenhar and Treacher Collins. The reported incidence of atresia varies between one in every 10,000 and one in every 20,000 children, and is twice as common in boys as girls (Understand hearing loss, n.d.).
- Head injury or injury to the ear can cause hearing loss.
- Wax or foreign bodies blocking the ear canal can cause hearing loss at any age. Such hearing loss is usually mild and can be readily corrected.
Hearing impairment can be of various kinds depending on its causes. The next section describes the types of hearing impairment including their causes, symptoms and treatment options.
3. Types of Hearing Impairment
There are mainly three types of hearing impairment:
3.1. Conductive hearing loss
3.2. Sensorineural hearing loss
3.3. Mixed hearing loss
3.1. Conductive hearing loss
Conductive hearing loss occurs when something is blocking sound waves from passing to the inner ear, through the outer and middle ear. Causes can include blockage of the outer ear or ear canal, an ear infection with fluid, malformation of the outer or middle ear, allergies (serous otitis media), perforated eardrum, impacted earwax (cerumen), infection in the ear canal (external otitis), Swimmer's Ear (otitis externa) and presence of a foreign body. It usually involves a reduction in sound level or the ability to hear faint sounds, speech tends to sound understandable, but only if it's loud enough and there isn't too much background noise. This type of hearing loss can often be corrected medically or surgically. If the condition cannot be addressed through medication or surgery, many people with conductive hearing loss may benefit from using traditional hearing aids or bone conduction hearing aids (Hearing Loss Explained, n.d.).
3.2. Sensorineural hearing loss
Sensorineural hearing loss is usually a result of a problem with the cochlea (inner ear), either through malformation or damage. This can also happen due to damage to the nerve pathways from the inner ear to the brain. Damage can occur from infections such as meningitis, as a side effect of certain medications described as ototoxic, malformation of the inner ear, head trauma or exposure to loud noise. SNHL reduces the ability to hear faint sounds. Even when speech is loud enough to hear, it may still be unclear or sound muffled. When present in both ears, sensorineural hearing loss will mean having difficulty understanding, even when speech seems loud enough. When in one ear, there may be difficulty locating sounds or hearing in background noise. This is the most common type of permanent hearing loss. Treatment for sensorineural hearing loss varies, depending on the severity of hearing loss and whether it has affected one ear or both.
Treatment for SNHL in both ears
Hearing aids can help most people with mild to moderate sensorineural hearing loss in both ears. For more severe levels of hearing loss, sometimes hearing aids do not help because sensorineural hearing loss causes sounds to become distorted. Amplifying sounds through hearing aids makes them sound louder, but not necessarily clearer. For severe to profound hearing loss, a cochlear implant is effective. It is an electronic device that is surgically implanted so it bypasses the damaged inner part of the ear to stimulate the hearing nerve directly. Unlike hearing aids which simply amplify sound, cochlear implants convert sound waves to electrical impulses in a way that works like natural hearing.
Treatment for SNHL in one ear
In mild to severe sensorineural hearing loss in one year, a conventional hearing aid is the most common treatment option. However, as hearing aids require some degree of useable hearing, they can’t help in the case of profound hearing loss. In profound losses, bone conduction implants can transmit sound through bone, from the damaged ear to the working inner ear on the other side. This makes it easier to understand speech in noisy situations and reduces the attenuation of sounds from the deaf side.
3.3. Mixed hearing loss
Mixed hearing loss is a combination of conductive and sensorineural hearing loss. In other words, there may be damage in the outer or middle ear and in the inner ear (cochlea) or auditory nerve. Genetic factors, overexposure to loud noise, certain medications and the normal ageing process can lead to sensorineural hearing loss. Birth defects, diseases, infections, tumours or masses and head injuries are all possible causes of both conductive and sensorineural hearing loss.This type of hearing loss ranges in severity from mild to profound. For people with mixed hearing loss, sounds can be both softer in volume and more difficult to understand. Depending on the degree of mixed hearing loss, it may be treated with medications, surgery, hearing aids or an implantable bone conduction hearing system.
4. Impact of hearing impairment on development of children
Disability in interacting normally: Hearing loss causes the impairment to become a disability by delaying speech development and thus inability to participate or initiate any conversation.
Academic achievement: Children with normal to profound hearing impairment have difficulty in learning abstract words like before, after, equal to, and jealous. They also have difficulty with function words like the, an, are, and a. Their overall vocabulary is weaker than other children of their age. Due to poor communication and language comprehension, their academic achievement is affected.
Construction of sentences and pronunciation of words: Children with hearing loss comprehend and produce shorter and simpler sentences than children with normal hearing. They have difficulty understanding and writing complex sentences, such as those with relative clauses or passive voice. Children with hearing loss often cannot hear word endings such as-s or-ed. This leads to misunderstandings and misuse of verb tense, pluralisation and possessives. Children with hearing loss often cannot hear quiet speech sounds such as "s," "sh," "f," "t," and "k" and therefore do not include them in their speech. Thus, their speech may be difficult to understand (Hearing loss, n.d.).
Social isolation: Children with hearing loss may not hear their own voices when they speak. They may have a speaking pitch that is too high. Their speech may sound like mumbling because of inadequate emphasis and speed of speaking. Since these children are not able to speak properly, hear others and at the same time other people find it difficult to understand their words, these children become isolated in social environment and often suffer from depression.
Economic impact: According to WHO (2014), children with hearing impairment do not receive quality education and in future find it difficult to get employment. Even if they do, the jobs are of low levels compared to general workforce. Thus, their choice of vocation is restricted and consequently source of income too.
References
Anatomy and structure of Human Sense Organs. (n.d.). Retrieved from http://www.scientificpsychic.com/workbook/chapter2.htm
Hearing Loss. (n.d.). Retrieved from http://www.asha.org/public/hearing/Hearing-Loss/
Hearing Loss Explained. (n.d.). Retrieved from http://listeningandspokenlanguage.org/Tertiary.aspx?id=1202
Impairment, Disability and Handicap. (n.d.). Retrieved from http://www.pediatrics.emory.edu/divisions/neonatology/dpc/Impairment%20MX.html
Ministry of Law, Justice and Company Affairs. (1992). The Rehabilitation Council of India Act, 1992 (No. 34 of 1992). New Delhi. Retrieved from http://www.svayam.com/pdf/the_rci_act-1992&amendement_act_2000.pdf
Ministry of Law, Justice and Company Affairs. (1996). The Persons with Disability Act (Equal Opportunities, Protection of Rights and Full Participation) 1995 (No.1 of 1996). New Delhi. Retrieved from http://meghpol.nic.in/acts/central/PWD_Act.pdf
Rehabilitation Council of India. (n.d.). Hearing Impairment. Retrieved from http://www.rehabcouncil.nic.in/writereaddata/hi.pdf
Understand hearing loss and its causes. (n.d.). Retrieved from http://www.cochlear.com/wps/wcm/connect/in/home/understand
WHO (2014). Deafness and hearing loss. Retrieved from http://www.who.int/mediacentre/factsheets/fs300/en/
WHO (n.d.). Disabilities. Retrieved from http://www.who.int/topics/disabilities/en/
