Cochlear Implants

Overview of Cochlear Implants in India

A cochlear implant is a device that helps with hearing. Cochlear implants are appropriate for people who already have hearing, especially if they do not benefit from hearing aids and cochlear implants is the only option left to listen well. The sound produced from cochlear implants is not the same as natural sound and the brain retrains itself to understand cochlear implant signals as sound. 

Patients who receive cochlear implants usually take 3-6 months after surgery to learn the meaning of the sounds they produce. Cochlear implants can be implanted in one or both ears, depending on the individual patient's needs. Adults usually have single ear cochlear implants, unless they have advanced irreversible hearing loss in both ears. Children requiring cochlear implants have to use cochlear implants in both ears if they have bilateral hearing loss otherwise it can be a disadvantage for them.

Adults of any age (from young adults to elders under 95 years of age) and children over 12 months of age who benefit from a cochlear implant are eligible to receive one. There are rare risks associated with cochlear implants, and complications occur only rarely.  The cochlear implant simply improves communication and drastically improves quality of life for many individuals severely suffering from hearing loss.

What Are Cochlear Implants?

Cochlear implants are electronic devices that assist individuals with hearing loss. Your doctor may recommend cochlear implants if you have moderate, profound, or severe hearing loss in one or both ears and you have had limited benefit with your hearing aids. You may also benefit from cochlear implants if you have benefited from hearing aids, but still don't understand speech to your satisfaction.

Cochlear implants do not restore hearing; however, they can improve speech understanding and the perception of other sounds.

Who Uses A Cochlear Implant?

Cochlear implants enable individuals with hearing loss to both receive and interpret sound, including speech. However, cochlear implants do not restore normal hearing, as they do not provide sound in the same way the ear does. Instead, they comprise instruments, and actuate the process of sound and/or speech into electric impulses that are later received by the brain.

Cochlear implants are not for everyone. For whom a person is selected for cochlear implants is evolving with growing knowledge of brain hearing (auditory) pathways, and changing technology.

Cochlear implants may be an option for children and adults. Candidates for these devices may have been born deaf or have lost their hearing after language acquisition. Children can be candidates as young as 1 year old now. The criteria for candidacy varies slightly for children and adults, but the principles are on similar guides:

• The person must be totally or nearly totally deaf in both ears and show little to no benefit from hearing aids. Any individual who can hear well enough through hearing aids is not a suitable candidate for cochlear implants. 
• The individual must be highly motivated. After the device is implanted, they must learn to use it. 
• The person must have reasonable expectations of what will happen after the surgery. The device does not restore hearing to "normal" levels. 
• Children must participate in programs that teach them to process sound. 
• To determine whether an individual is a candidate for a cochlear implant, the individual must be evaluated by an ear, nose, and throat (ENT) doctor (otolaryngologist). Individuals will also require specific types of hearing tests with their hearing aids in place. 
• Individuals may require a CT scan or MRI of the brain and the middle and inner ear. 
• Individuals (especially children) will also require a psychological evaluation to determine if they are a good candidate.

How It Works

Sounds travel through the air and are usually perceived in the ear by first causing the eardrum to vibrate, then the middle ear bones. This transmits the wave of vibration into the inner ear (cochlea). The cochlea translates the wave into electrical signal, which travel via the auditory nerve to the brain. 

A person who is deaf has a non-functioning inner ear. The cochlear implant is intended to replace the inner ear's function by converting sound into electrical signals. The energy produced by sound can be used to electrically stimulate the cochlear nerve (the nerve of hearing) to send "sound" signals to the brain. 

• Sound is digitally captured by a microphone worn close to the ear. This sound is transmitted to a speech processor, which is usually worn behind the ear and is often attached to a microphone. 
• The sound that was picked up by the microphone is analyzed and converted into electrical signals, which are sent to a surgically implanted receiver located behind the ear, and then through a wire into the inner ear. 
• From the inner ear, the electrical impulses are transmitted to the brain.

Types of Cochlear Implants:

Single-Channel Cochlear Implants

Earlier implant designs feature a single electrode that stimulates the hearing nerve. There are fewer channels for sound perception in these implants, and the sound quality and speech recognition are relatively poor.

Multi-Channel Cochlear Implants

This is the most commonly used device today. These implants consist of multiple electrodes that stimulate different regions of the cochlea. Multi-channel devices can stimulate sites with greater specificity, provide a better representation of sound frequencies, and improve speech perception.

Hybrid Cochlear Implants

Hybrid cochlear implants serve the dual function of cochlear implant technology and hearing aids. Hybrid cochlear implants are designed for people with low-frequency hearing loss but who have lost high-frequency hearing.

Cochlear Implants with Components Behind the Ear (BTE)

In the case of BTE cochlear implants, the user wears the external components behind the ear: a microphone for capturing sound, a speech processor that analyzes the sound and creates electrical signals, and a transmitting coil that sends these signals to the implanted component. These external components are connected to the implanted receiver-stimulator with a thin wire that passes through the skin. BTE cochlear implants are widespread and provide excellent sound quality.

Receiver-in-the-Ear (RITE) cochlear implants

In RITE cochlear implants, the receiver-stimulator is built into the external portion of the device, so there is no wire connecting the external and internal parts; sound signals are sent wirelessly to the implanted receiver-stimulator. The patient still wears a microphone and speech processor behind the ear. RITE cochlear implants are smaller and sleeker than BTE implants.

Fully Implantable Cochlear Implants 

All of the components of fully implantable cochlear implants are implanted under the skin. This means the microphone, speech processor, and receiver-stimulator are all under the skin. There is no hardware worn behind the ear, making the implant less obvious. However, the surgery is also more complicated for fully implantable cochlear implants. They offer the convenience of not having to worry about external components, but they are used less often than BTE or RITE implants.

Procedure:

Assessment: The first step is a complete assessment by the multi-disciplinary team of specialists which includes an audiologist, an ENT surgeon (ear, nose, and throat doctor), and a speech-language pathologist. The assessment will consist of hearing tests, a review of your history, and conversations about your ultimate communication needs and goals. The team will determine both the degree of hearing loss, the health of the inner ear, and overall health to determine eligibility for a cochlear implant.

Surgery: If you are deemed an appropriate candidate, their surgeon may advise proceeding with cochlear implant surgery. This procedure is usually performed under general anesthesia. The surgeon will make a small incision behind the ear, and make an opening in the mastoid bone to access the cochlear nerve. The electrode array contains small electrodes that are gently inserted into the cochlea through the opening. Your doctor will place the electrode array to ensure as many electrode contacts as possible come into contact with the auditory nerve. The receiver-stimulator is placed under the skin behind the ear and contains the electronics that convert sounds into electrical signals. Once the receiver-stimulator is in place, the incision will most likely be closed with either stitches or surgical glue.

Recovery and Activation: Generally, recovery from surgery is a couple of weeks after the procedure. During this time the incision heals, while avoiding incurring changes to the surgical site. After that process you will return to the cochlear implant center for the purpose of activation. Activation is when you will fit and program the external components of your cochlear implant (the microphone and speech processor) for you specifically. The audiologist will take detailed notes on your level of comfort and hearing to adjust the settings (volume, sensitivity, and number of electrical channels) to suit your journey.

Rehabilitation and Follow Up: After activation, you will take part in a rehabilitation phase. This phase is crucial for your adjustment to the cochlear implant while you learn how to interpret sound from your device. Rehabilitation may include auditory training, speech therapy, and counseling. Audiologists and/or speech-language pathologists will work together with you to enhance your ability to understand speech, improve listening skills, and develop appropriate communication strategies. You will likely have follow up appointments with your doctor so they are aware of your progress, adjust suitable settings on your cochlear implant, and to answer any questions or concerns you may have.