There are two parts to a cochlear implant: the external and the internal.

1. External Sound Processor: This piece sits behind and over the ear with an earhook and looks similar to a traditional behind-the ear-hearing aid. The microphones capture, filter, and process sound and then translate the sound into digital information. The digital information is sent through the external transmitting coil.
2. External transmitting coil: The translated sound gets sent through the external transmitting coil which then, via an FM signal, transmits across the skin with a magnet. The internal implant converts the digital information into electrical signals and sends them to tiny electrodes inside the cochlea (inner ear).
3. Electrode array: The electrode array receives the electrical signals and stimulates the auditory nerve (hearing nerve). The cochlear implant takes the place of hair cells (cells inside the inner ear that stimulate the auditory nerve) to electrically stimulate the auditory nerve.
4. The auditory nerve receives the stimulation and sends the information to the brain, producing a hearing sensation.

How a Cochlear Implant Processes Sound

The goal of all cochlear implants is to electrically encode speech in a manner in which it will be understood in a variety of listening environments. Each cochlear implant manufacturer utilizes different speech-coding strategies. Speech-coding strategies are a set of rules used to convert acoustic signals into electrical stimulation. The objective is to convey high-fidelity electrical representation of the incoming sound, thereby allowing the cochlear implant user to perceive sound in a similar way to a normal hearing listener, even with a severe and/or profound hearing loss.

A cochlear implant considers all three dimensions or acoustic characteristics of sound when utilizing sound-coding strategies: intensity/amplitude (loudness), frequency (spectral/pitch), and temporal (time).

The frequency is conveyed by the site of stimulation in the cochlea. In other words, it pertains to the specific electrodes along the array in the cochlea that are being stimulated. The amplitude is conveyed by the different amounts of stimulation, or current levels, the electrodes receive. Finally, the timing cues are conveyed by the rate, or how quickly the electrodes are being stimulated, and the pattern of the stimulation.

When to see an Audiologist about a Cochlear Implant

• Difficulty communicating in everyday life even with powerful hearing aids
• Avoiding social situations because you do not understand what is being said
• Difficulty understanding when not face-to-face and relying more on lip-reading to understand speech
• Difficulty understanding on the telephone and therefore avoiding answering and making phone calls
• Feelings of isolation from family and friends
• Desire to hear/understand more sound

Updated 2024 FDA Criteria for Cochlear Implant Candidates

In 2024, the FDA updated its criteria for cochlear implant candidacy to reflect advancements in technology and improved understanding of patient outcomes. The new criteria include: 

1. Expanded Audiological Criteria: Individuals with moderate to profound sensorineural hearing loss (70 dB or greater) in both ears can now be considered for cochlear implants. Additionally, individuals with single-sided deafness and severe to profound asymmetrical hearing loss may qualify as candidates.
2. Speech Recognition Scores: Candidates with word recognition scores of 60% or less in the best-aided condition on sentence recognition tests may qualify. 
3. Age Considerations: Children aged 9 months and older with bilateral severe to profound sensorineural hearing loss are eligible, provided they show limited to no benefit from binaural amplification. 
4.  Progressive Hearing Loss: Individuals with rapidly progressive hearing loss that leads to severe to profound levels within a short period may qualify. 

Hybrid Cochlear Implants: Individuals with better low-frequency hearing but severe to profound high-frequency hearing loss may benefit from hybrid cochlear implants that combine acoustic amplification with electrical stimulation.

Candidacy Evaluation for Cochlear Implants

The candidacy evaluation process for cochlear implants involves several steps to determine if an individual is a suitable candidate. These steps include:

1.  Audiological Evaluation: An audiologist performs a comprehensive hearing test to assess the degree and type of hearing loss in both ears. This evaluation includes pure-tone audiometry, unaided speech perception testing, and aided speech perception testing to determine the extent of hearing loss and the benefit of current hearing aids for speech understanding in each individual ear. During this appointment, it is typically decided which ear should receive the cochlear implant. The discussion during this appointment is educational as well as collaborative for decision-making. 

2. Medical Examination: An Otolaryngologist (ENT specialist) conducts a medical evaluation to ensure there are no contraindications for surgery, such as middle ear infections or other medical conditions that could affect the outcome of the implant.

3. Imaging Studies: Imaging studies, such as MRI or CT scans, are performed to examine the anatomy of the cochlea and auditory nerve to ensure they can accommodate the implant. 

4. Speech and Language Assessment: For children, a speech and language pathologist evaluates speech and language development to establish a baseline and plan for post-implant rehabilitation. Adults may also undergo speech and language assessments to set realistic post-implantation goals. 

Counseling and Education: Candidates and their families receive counseling about the cochlear implant process, including surgery, device activation, rehabilitation, and realistic expectations for outcomes. 

Factors that may Affect Adult Performance with a Cochlear Implant

• Length of deafness
• Status of cochlea
• Pre-implant hearing experience
• Number of nerve fibers remaining in the cochlea
• Commitment to the rehabilitation process
• Cognitive factors
• Family support
• Personality and motivation
• Other health issues

General Benefits for Post-Lingually Deafened Adults

• Improved ability to hear soft sounds
• Improved ability to understand speech
• Ability to converse on the telephone
• Improved speech reading ability when combined with auditory information
• May have improved understanding in noise
• Improvement in monitoring the loudness of own voice
• Feeling less isolated and an improvement in daily life

General Benefits for Pre-lingually Deafened Adults

*Considered for those who are auditory/oral

• Improved ability to hear soft sounds
• Improved ability to understand speech
• Improved speech reading ability when combined with auditory information
• Recognition of many environmental sounds
• Improvement in monitoring the loudness of their voice
• Feeling less isolated and more involved in daily life

Important Considerations!

Using a cochlear implant is a whole new way of hearing sound. Therefore, it may take days, weeks, months, or years to be considered a successful user. It is important to speak with your audiologist about proper expectations. These expectations are considered different for every person.

What is the Protocol associated with Receiving a Cochlear Implant?

Clinical protocols vary from clinic to clinic, though there are some general protocols that are shared among the hearing health professional community.

A cochlear implant candidate will need to meet the requirements by undergoing a medical evaluation (including a general health assessment and imaging (e.g. CT, MRI)) and a full audiological evaluation (hearing profile) with and without appropriately fit hearing aids. Additionally, the candidate must meet all FDA requirements to be considered.

The candidate and family/friends of the candidate must undergo extensive counseling on appropriate expectations and be educated on the cochlear implant process, such as the need for frequent follow-ups with the audiologist. Further, they should be educated on what a cochlear implant is, how it looks, and how it works.

Above all, the patient needs to have a desire to be part of the hearing world.