To restore a special sense
Dr. MOHAN KAMESWARAN
Early diagnosis and intervention and the success of cochlear implants can help the hearing-impaired children overcome their disability.
Corrective procedure: A display on cochlear implants. Photo: G.R.N. Somasekhar
PADMAJA is 10 months old. But she is a special child. She was born profoundly deaf in both ears. Her hearing loss was detected when she was three months old. Padmaja received a Cochlear Implant when she was only eight months old.
Two months later she began responding to the sounds. She also started vocalising and calling out to her parents.
Padmaja is one of the few lucky children whose problem was corrected early. By the time she is 18 months old, she is likely to develop as much language skills as a child any of her normal hearing peers.
Congenital hearing loss is very common among Indian children. The estimated incidence varies from one to four per 1000 live births.
Padmaja is an Indian child born to a middle class family. But her parents were very well informed about their options and were fast to act on the corrective procedure without delay.
This is the ideal scenario and any child with congenital profound deafness affecting both ears can develop spoken language skills and be integrated into a normal school by three or four years, if they are exposed to "Early Intervention".
Profound deafness affecting both ears among children also causes language deprivation. If detected early ideally below one year and treated properly, the child overcomes the disability and acquires speech and language rapidly, bridging the gap with normal peers by three years.
Here, the operative phrase is "Early Intervention". Any disability whether auditory, visual or physical has better chance of correction if intervention to rectify it is adopted at the earliest.
This is due to an interesting phenomenon in the brain called "Neural Plasticity". In simple terms Neural Plasticity is the ability of the young brain to acquire new skills and information. This is at its best in infancy and early childhood and is lost, as we get older. Thus the critical period for speech development is from birth to three to four years.
Early Intervention requires an even earlier detection and diagnosis, ideally within a few days of birth. In advanced societies, neonatal hearing screening is mandatory and is usually performed soon after the birth.
Today technology to detect deafness and quantify it even in newborn children is available. But these facilities are under utilised. A host of very sophisticated audiological tools known as Oto Acoustic Emission (OAE), Brainstem Evoked Response Audiometry (BERA), Auditory Steady State Response (ASSR) help accurately diagnose deafness even when the child is only a few days old.
Once a child is diagnosed, the immediate and anticipated reaction of the parents and immediate family is one of denial. Doctors or the audiologists need to counsel the family, help them cope with the situation and encourage them to look forward to solutions to overcome the problem.
Often when the family is told about the excellent options available for a hearing impaired child, the chances of acceptance is much better. Once the family accepts the handicap, half the battle is over and rehabilitation can begin.
The type of intervention required depends on several factors. Chief among these is the degree of impairment.
When a child has a fair degree of residual hearing, the correct intervention would be fitting "optimised" hearing aids. "Optimisation" means fitting the child with a hearing aid appropriate to its degree of deafness. The aim is to get the child's corrected hearing within an accepted range of hearing.
Today a variety of good quality hearing aids are available analog or digital, body worn (for small children) or ear level for older children.
When fitting a hearing aid, a competent audiologist has to assess the child's residual hearing, look at the hearing aid's performance and fit the child with an appropriate instrument. Equally important is the ear mould, which has to be custom made to suit the shape of the child's ear.
If a child has profound or even total deafness, it has very little or virtually no residual hearing. In such a case hearing aids do not make scientific sense. Such a child needs Cochlear Implants.
Cochlear Implants represent a successful human attempt at restoring a lost special sense. First perfected in its present form by Prof. Graeme Clarke of Melbourne, Cochlear Implants are a set of electrodes implanted surgically into the inner ear.
An external part called the speech processor (which resembles a hearing aid) collects sound, processes it and stimulates the implanted electrodes across the skin. The external device and the implant under the scalp come together by magnetic coupling.
When sound reaches the implant and the fine neurons of the cochlea, they decode the sound and send it to the brain to be perceived as sound.
Fortunately, over 99 per cent of the children born deaf (even totally deaf) have functioning nerves of hearing. It is the inner ear, or cochlea, which is damaged. Thus when the damaged cochlea is bypassed by the implant and the intact neurons are stimulated, hearing can be restored.
Also the cochlea, which is a pea-sized organ in the inner ear, is fully developed even before birth. This makes cochlear implantation possible in very young children like Padmaja.
Over 1,00,000 Cochlear Implants have been done worldwide since the early 1980s; in India, nearly 1,000 implants have been done at over 20 centers.
But a successful outcome is determined by the time and effort put into rehabilitation after the implantation. Thus any good Cochlear Implant centre should have a well-developed rehabilitation centre.
Cochlear Implantees need "Auditory Verbal Therapy" (AVT), which is different from the traditional oral rehabilitation. In Auditory Verbal Therapy, the emphasis is on making the child listen and speak normally, not on lip reading and visual cues.
A successful Cochlear Implant will aim at a comprehensive programme comprising early detection, early intervention and intensive post-operative rehabilitation for at least one year.
An estimated one million children in India need Cochlear Implants. Every month, over 20 families opt for Cochlear Implants for their profoundly hearing impaired children in India.
This is mainly after coming in contact with other children with implants who have learnt to speak and interacting with their families on the benefits and excellent outcome.
India is now poised to take challenges of deafness head on. What is urgently needed is a National Deafness Prevention Programme to address the issues with a scientific and social commitment.
The author is a Consultant ENT Surgeon, Madras ENT Research Foundation, Chennai, and President Of Cochlear Implant Group of India. E-mail: firstname.lastname@example.org Website: www.merfmk.com
Names have been changed to protect the privacy of the families.
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