Electric Acoustic Stimulation
The Electric Acoustic Stimulation (EAS) system combines the technology of cochlear implants with hearing aids. It is designed for people with partial deafness who have useful hearing left in the low frequencies but can no longer hear high frequency sounds.
Individuals with partial deafness are able to understand one-on-one conversations in quiet surroundings reasonably well, but cannot follow conversations in noise. They often understand male voices better than female ones.
How does Electric Acoustic Stimulation works (EAS)?
The cochlear implant component stimulates the part of your cochlea which is responsible for high-frequency sounds, while the ‘hearing aid part’ takes advantage of your natural residual hearing by turning up the volume on the low-frequency sounds. Together, it covers the full hearing range.
As with a cochlear implant, a small audio processor is worn behind your ear. It is connected with a cable to a transmitter coil, which sits on the outside of your head, over the implant. The coil stays in position with the help of magnets.
During surgery a thin, flexible electrode is inserted at the base of your cochlea in the inner ear. This part is responsible for hearing high-pitched sounds. The inner (apical) part of the cochlea, which is responsible for the low-pitched sounds, remains intact.
An ear mould, which directs sound into your ear canal, is connected to the audio processor.
How EAS works:
- A microphone inside the audio processor picks up sound. Both high and low frequency sounds are processed simultaneously.
- Low-frequency tones are amplified and sent through the ear mould into your ear canal.
- These low tones take the natural path to your cochlea. The hair cells in the apical region, which deals with low-frequency tones, receive the amplified sound signals.
- The audio processor digitally analyses and codes sound into a special pattern of coded electrical signals.
- These signals are sent to the coil and transmitted through your skin to the implant.
- The implant creates electrical pulses from the coded signals.
- These pulses are relayed via the electrode contacts to the different parts of the cochlea.
- The hearing nerve receives both acoustic and electric sound information at the same time and transfers it to the hearing part of your brain, where it is processed.
Can you get it on the NHS?
The same NICE guidance for cochlear implants applies to EAS systems. A thorough assessment will be carried out to determine suitability, as with cochlear implants. If criteria are met, the NHS pays for the EAS system.
Who is EAS suitable for?
Hearing tests and a medical examination will determine whether an EAS system is a good option for you or your child. Criteria include:
- Mild to moderate hearing loss in the low frequencies and severe to profound hearing loss in the high frequencies.
- No sufficient speech understanding even with optimally fitted hearing aids.
- No progressive hearing loss – if your hearing loss is gradually getting worse, the EAS system may no longer work well for you within a few years. A stable natural residual hearing is essential.
- No cochlear malformations.
- Willingness to do rehabilitation.
Advantages of Electric Acoustic Stimulation
- Better speech understanding Studies have shown that EAS users achieve on average 50 percent better speech understanding than with hearing aids alone.
- Better pronunciation as users hear their own voice more clearly
- Telephoning becomes easier due to better speech understanding
- Active participation in school and work is easier
- More music enjoyment as users hear the high-pitched tones
- Better understanding of speech facilitates communication in groups and in noisy environments
- Higher quality of life
What to look for in EAS system
- Soft and flexible electrodes – The softer and more flexible the electrode, the lower the risk that it will cause trauma or damage to the delicate structure of your inner ear. This will protect your residual hearing.
- MRI safety– It’s important to know whether your device is compatible with MRI scanners used for diagnostic medical tests, and to what degree.
- Compatibility with future sound-coding strategies – This means it’s possible to upgrade your internal implant without surgery as future advances in technology are made.
- Backwards compatibility – An audio processor that is ‘backwards compatible’ is compatible with an implant that you may have had for several years.
- Intelligent sound adaptation – Your audio processor detects when you change environments and adjusts programs and volume automatically, so you don’t have to keep making manual adjustments.
- More than one microphone – This sharpens the sounds in front of you for better hearing in noisy settings.
- Wind Noise Reduction – So it’s easier to hear outdoors.
- Water-resistance – so your device is splash-proof, or offers waterproof accessories so you can swim wearing your audio processor.