Overcoming Deafness

Deafness is an invisible handicap. Deaf babies as well as adults cannot hear themselves crying. They don’t turn their heads when the pressure cooker whistles or the phone rings. In fact, by one year of age, when most other children speak a word or two, congenitally deaf children are mostly silent. Often parents of such children are told ‘some children are slow’, ‘you are over anxious parents’. And as a result valuable time is lost and the children live in a silent word sans words or language. In terrible loneliness, they watch others around them open and shut their mouths; but to the children it is just a silent movement. They cannot speak, for speech follows hearing. In fact after five or six years of age, language can be taught to a limited extent only. Persons who lose their hearing after they have learnt language (post lingual) may lose the clarity of their speech after a certain period of time, but do regain the skill if they are systematically retrained.

When the hearing loss is formally diagnosed, hearing aids are advised. Hearing aids help. They amplify and occasionally distort but the sound does get heard. Cochlear Implants come into the picture only when there is no benefit from the hearing aids, provided the auditory nerves and the hearing centers of the brain are functioning well. Cochlear implants have revolutionized hearing rehabilitation. They are a reliable and effective treatment for those with bilateral severe to profound sensorineural hearing loss receiving little or no benefit with hearing aids. Children who are born deaf should be implanted as early as possible because the critical period of language acquisition decreases rapidly after the age two years. Adults who have learnt language skills (post-lingual) and have lost their hearing due to illness or injury are likely to be benefited by the help of the Cochlear Implant provided it is done within five to six years of the hearing loss.

So what is a cochlear implant? It is an electronic device that performs the function of the damaged or absent hair cells in the cochlea of the inner ear by providing electrical stimulation to the auditory nerve fibres. It is a sophisticated piece of technology comprising two parts, one which is surgically placed inside the ear (the implant) (Fig.) and the other (the processor and the transmitter) (Fig.) which is outside. The latter collects the sound waves and translates them into electrical impulses. The inner implant, which is surgically placed under the skin just behind the ear, delivers these impulses to the nerve fibres, bypassing the abnormal part of the cochlea. The implanted device has a built-in magnet, which helps the proper positioning of the external part.

The surgically implanted part comprises an electrode array and a reference electrode and the external components (speech processor, coil, etc.). They contain powerful custom made chips capable of processing large amounts of information at a rapid rate. They can generate thousands of sequential, non-overlapping stimulating pulses per second and have been designed according to the highest safety and reliability standards. These characteristics make them capable of utilising a wide range of speech processing strategies, some with the ability to incorporate future developments in speech processing.

The electrodes, which are inserted into the cochlea of the patient, are in pairs (12 to 22, depending on the make of the implant). There are sufficient gaps between the electrodes to avoid overlapping of information and to maximize speech understanding. For cases of cochlear ossification and malformation, a variety of electrodes, like the split array which are available. Although the body-worn processors are more common today, some implants do have a behind-the-ear (or BTE) option.

How is the patient for cochlear implant evaluated? Once a severe to profoundly deaf patient not benefiting with hearing aids comes to the ENT surgeon, a battery of hearing tests (pure tone audiometry, impedence, BERA, SSEP), and radiological evaluation (CT - MRI) of the anatomy of the mastoid and inner ear are done. Absence of an auditory nerve would eliminate candidacy for an implantation. The patient then undergoes psychological and neurological evaluation to rule out any mental handicaps / behavioral disorders which may delay post-implant rehabilitation. Once the patient is selected for implantation, then the routine pre-operative hematological tests are done.

Children aren’t the only ones to be implanted. Postlinguistic patients who have lost their hearing to illness (eg. meningitis or other viral infections) or injury (eg. Trauma to the skull/brain in a road accident resulting in hearing loss) after they have learnt speech and language, benefit with the Cochlear Implant, specially if the implantation is done as close to the time of the hearing loss as possible.

It is important to stress here that not all deaf persons can be implanted. At Hinduja Hospital, Mumbai, patients are evaluated by the ENT surgeon, the audiologists, a neurologist, a psychologist and a social worker to ensure that the patient will obtain benefit from the implant. It is difficult to predict how much the patient will benefit with the implant. Expectations have to be realistic and are explained in detail to the recipients and their families. Parents of children and patients themselves are made to understand the extent of use and the limitations of the implant.

The surgery itself is done under general anesthesia. A postaural incision is made and a cortical (simple) mastoidectomy is done. The middle ear is opened via the drilling of the bone behind the ear (i.e. a cochleostomy is done through the facial recess). A well is drilled in the temporal bone (just above the mastoid) to place the receiver. The electrode array of the implant is inserted into the cochleostomy and the cochleostomy is sealed with tissue. The wound is then closed. The dressing stays for eight days, after which the sutures are removed in the clinic.

Post implantation, there is a process known as mapping/ fitting which, in a monitored way, programs the maximum and minimum volume and the frequencies that can be heard by the individual. This is a key part of the postoperative management of all implantees and occupies a significant proportion of the postoperative clinical time. It is done with the help of special software. The first mapping is called the "switch-on" and is done approximately three weeks after the surgery by a specially trained audiologist. Subsequently, mapping is done regularly at progressively spaced out intervals and the patient’s individual threshold and maximum comfort levels are set. After ‘switch on’, the sessions are weekly for a month, then fortnightly for four turns, then monthly for six months, and subsequently once biannually for a year or two. After that mapping is done annually to check out the status of the working of the electrodes.

For the implant users to perceive the desired range of acoustic signals from their environment, the features of these sounds must control the electrical stimulation within the cochlea in an appropriate way. The implant system is designed to present acoustic information, in particular speech, to patients in a usable form. The initial aim of speech processor programming is to optimize the information provided for a particular patient. Along with this aim, there is the need to make the program comfortable for patients to listen to in their everyday life.

Speech processor mapping requires establishing which electrodes produce useful hearing sensations and measuring a threshold level (T) and the maximum comfortable level (C). The T level refers to the smallest amount of current that can consistently elicit a hearing sensation. The C level is the maximum stimulation level that does not produce an uncomfortably loud sensation. The audiologist has to be aware of the location of the implant (from the surgical report and confirmed by an xray), as there is a possibility that some active channels may be outside the cochlea. This determines both the number of channels that are likely to be available for speech processing and the most appropriate stimulation mode. In adult patients, programming is a relatively straightforward and easy task. In infants and young children the stimulus response and judgement tasks involved maybe beyond their cognitive abilities, hence the co-operation during long sessions can be trying. Many objective test techniques are available which are used in early intervention/diagnosis/treatment. In the near future, these tests would be essential in implant centers.

Implanted adults have initially described the sounds they hear like those in ‘the cartoon network’. One post-linguistic adult patient said that in the beginning he couldn’t make out the difference between a sneeze and a car horn and a human voice from the click of a lock. After the ‘switch-on’, it was like a cacophony. He heard only noise! Then, with specialized auditory verbal therapy, he learnt to distinguish between the various sounds, voices and words. Over a period of time he regained his original speech and clarity and was able to used a telephone and enjoy a television program.

Post implantation Auditory Verbal Therapy is a MUST for all implantees. It teaches them to identify, discriminate and comprehend what they hear. All patients need to be trained to associate various sounds with their meanings.

Currently cochlear implants provide minimal benefit to a prelingual (one who is deaf before being exposed to language) person over the age of about seven or eight years, or one whose nerves or auditory centers are abnormal. After cochlear implantation such patients may be taught to identify environmental sounds such as mewing, mooing, honking, whistling, barking, etc. But teaching language or speech is difficult unless they have been taught the same with hearing aids from early childhood.

Early detection of deafness and education through specialized therapy and training is therefore of the utmost importance, and given at an early age reaps maximum benefit. In fact, some schools for the deaf in Mumbai insist on infant training programs.

At Hinduja Hospital, Mumbai, which is one of India’s leading centers for Cochlear Implantation, Dr. M. V. Kirtane has operated over a hundred and eighty such patients. There are three companies whose products are available in India: Nucleus (Australian), Med-el (Austrian) and Clarion (American). The suppliers are Pika (Bangalore), Alps (Delhi), and Advanced Bionics (Bangalore) respectively.

In India, there have been over 600 Nucleus Cochlear Implants, and about 200 Med-els. The figures for Clarion were not available. The ages of the patients range from 10 months to 78 years.

The names of the different models are: Nucleus – Nucleus 24 and the latest Nucleus Freedom; Med-el – COMBI 41 and COMBI 40+; and Clarion – HiRes 90 K models. These come with a variety of processors.

The cost of the device varies from Rs. 4,79000 to Rs. 9,48,000 depending on the model and the company. Add to this the fees for the therapists, batteries for the speech processor, and replacement cost for the delicate wires when they break. Chargeable batteries are cheaper options in the long run and are available now with some makes of the implants. Over the years competition between the three companies manufacturing cochlear implants has proved an advantage to customers motivating the companies to provide good after-sales service as well as competitive rates.

Patients have to raise funds with the help of their employers, charitable and religious trusts, family, through advertisements for help via media, even bank loans.

One has to see the difference the cochlear implant makes to a person who is otherwise doomed to a life of silence, loneliness and deep despondency. Adult patients who are able to tell of their experiences, tell of their despair pre-surgery and the renewal of their life post-implantation. Parents whose children have been ridiculed, whose lives were caged in daily despair narrate tales of success in school and social circles.

Yes, Cochlear Implants are expensive. However, they are designed to last through a child’s lifetime of around 75 years. And they enhance the quality of life. A deaf individual who would have otherwise been permanently dependent on family, society and government can become a productive member of society because of the reduced degree of disability and hence the quality of life is improved immensely. Cochlear implants, therefore, offer a great way to overcome severe to profound deafness in selected candidates.