science moment

Hearing Aids:

[Plain Text: Hearing Aids]

There are many different types of hearing aids. Which type someone uses will depend on their hearing curve, the features they want, and the type of hearing loss.

1. Receiver in Canal.

Receiver in Canal (RIC) hearing aids are the newest type, and currently the most commonly prescribed. They have a small behind-the-ear component with directional microphones and processors, and are connected by a thin clear wire to an in-ear speaker, which is covered by a piece called the dome.

RIC are most commonly prescribed for: mild to moderate hearing loss (although they can be useful for some people with severe hearing loss), high-frequency hearing loss, noise-induced hearing loss, tinnitus, and auditory processing disorder. RIC are also available over the counter.

Benefits: small and discrete, fairly powerful, best integrated noise filtering systems, highest mapping customizability.

Drawbacks: sizing is not infinitely customizable, not good for more severe deafness, usually don't come in fun colors, difficult to use with low dexterity.

There are several different dome types, as I mentioned. Domes are soft silicone or plastic pieces fitted in diameter to the ear canal, but come in a few different shapes depending on the type of hearing loss. I'll talk about the most common ones, but there are a few other rarer custom types.

Open/Vented domes have slits cut in the silicone. They are the weakest at keeping sound trapped, but have the lowest occlusion effect (hearing your own voice loudly). They are good for mild to moderate hearing loss, but they can cause a lot of feedback, especially at higher frequencies, so they're most useful for high-frequency hearing losses. The amount of vents in the dome can be adjusted to reduce leakage.

Closed domes do not have slits or have very few slits. They keep more sound trapped, but have higher occlusion. They are good for moderate broad-spectrum and low-frequency hearing loss, since they allow less high-frequency noise to escape.

Power domes have no slits and often have multiple layers for maximum amplification. They have the highest occlusion effect, although people using power domes typically have hearing loss in the range of 60-80 dB, so occlusion is often necessary to hear one's own voice. Power domes can make the ear pressure feel unbalanced since there are no vents.

2. In the Ear / Completely in Canal.

In the Ear (ITE) and Completely in Canal (CIC) hearing aids are a less popular, but available, type. They feature a solid combined processor and speaker that sits in the ear canal. There is usually a small wire or clear plastic loop that fits along the curve of the outer ear both to keep it in place and to pull it out.

ITE/CIC are most commonly prescribed for: mild-moderate hearing loss when RIC is not preferred or available.

Benefits: no behind the ear component can be more comfortable, microphones in the ear have highest directionality, subtle.

Drawbacks: fewer features available, higher occlusion effect, can fall out more easily.

(There are some ITEs that have a behind-the-ear component for volume/power control and structural support, but the processor, microphones, and speakers are all in the canal piece.)

3. Behind the Ear.

Behind the Ear (BTE) are the most powerful type of hearing aid. The microphones, speaker, and processor are all present in the behind-ear component, which is larger than other types of hearing aids. This component is connected by a replaceable plastic tube to a mold, which is custom-fit to the user's ear and allows for maximum sound retention/amplification. Like domes, there are several types of molds.

BTE are most commonly prescribed for: severe to profound hearing loss, moderate or higher low-frequency hearing loss, children.

Benefits: sizing is fully customized, easy to use with lower dexterity, good for athletics (less likely to fall out), highest aesthetic customization, most powerful amplification.

Drawbacks: larger size, high occlusion, higher risk of ear infections, molds must be replaced as ear shape changes, tubes must be replaced regularly.

There are lots of different mold types. An ear mold is custom fit by creating a cast of the user's canal and ear shell. More or less of the "shell" of the ear can be covered by the mold. All molds have a vent hole to allow moisture to escape, but some molds have more holes cut into them to allow airflow or reduce occlusion. Some molds are hollow, while others are solid. (Molds can also come in lots of fun colors, including marbled or glittery, although insurance won't always cover these.)

There are too many types of molds and considerations to really get into exact types here, but if you look up behind the ear hearing aids there are tons of references online. [One type of mold I've seen a lot in real life but that I can't find the name of online are sort of square-shaped solid (often colored) plastic with lots of holes in them. They remind me of a waffle.] In general, the more severe the hearing loss, the less "air space" there's going to be in the mold.

4. Bone Conduction.

Bone Conduction hearing aids (BCHA) are probably the closest-looking in real life to those headphone ones, although many of the over-the-counter devices calling themselves BCHAs that look like headphones are in fact just bone conduction headphones. Prescribed BCHAs are often two individual rectangular devices, attached via stickers or a headband. There are a few that go behind the ear, although no component of the aid is in the canal.

BCHAs are bone conduction rather than air conduction, which means they get the sound to the cochlea by vibrating the skull bones rather than sending sound through the middle ear. BCHAs are often temporary aids (see BAHA in the CI section of this post).

BCHA are most commonly prescribed for: severe conductive or mixed hearing loss, microtia/atresia, and young children.

Benefits: more powerful and safer long-term for conductive hearing loss, typically no in-ear or over-ear component.

Drawbacks: require an external component (stickers or headband) to stay attached.

5. Airpods / Actually just headphones

Did you know, Airpods were recently approved by the FDA as over-the-counter hearing devices? The noise filtering technology makes smart wireless headphones a possible alternative for mild hearing loss, auditory processing disorder, tinnitus, or anyone who can't get prescription hearing aids. These are not a long-term solution, nor are they used by audiologists, but for people who just need a bit of a boost, having their headphones in all the time might be their way of navigating the world.

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All hearing aid types have their benefits and drawbacks, and no aid will ever be perfect for someone. Even the best hearing aids available can't make someone become Hearing. Some people who are severely to profoundly deaf report hearing aids giving them around 60-80% of what a hearing person can hear, and this number improves with decreasing severity of hearing loss. Still, nearly all d/Deaf/hoh people struggle to some degree with auditory processing. They may use hearing aids to give them general awareness of background noise (eg fire alarms), or for a boost while lip-reading, even if they don't help in understanding noise more generally. Hearing aids can also die or malfunction, removing the benefits they provide.

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Cochlear Implants:

[Plain Text: Cochlear Implants]

Cochlear Implants, or CI, are surgically implanted devices that stimulate the cochlea.

More on CI in one second, because I promised a return to BAHAs, which are a type of surgically implanted hearing aids. They get to go in this section because they are implants.

BAHA stands for bone anchored hearing aid (as opposed to BCHA, which stands for bone conduction). BAHA are the long-term alternative to BCHAs. A titanium plate is anchored to the skull, and an external hearing aid component attaches to the plate and vibrates it.

BAHA are most commonly prescribed for: severe to profound conductive hearing loss, microtia/atresia. (One of the major use cases for BAHA is Treacher-Collins Syndrome, which often causes bilateral microtia. Since the hearing loss is purely conductive, and traditional hearing aids do not typically fit people with microtia even without atresia, BCHA/BAHA are the best aids.)

Back to CIs. Unlike BAHAs, cochlear implants are implanted into the cochlea to directly stimulate the auditory nerve. They bypass the outer, middle, and inner ear systems, so they are useful for any type of hearing loss.

In order to qualify for a CI, one needs profound hearing loss across all or most frequencies, and the presence of both the cochlea and the auditory nerve (CI won't work without those structures). Someone can qualify for a CI in one ear but not the other; even if someone is qualified to receive implants in both ears, they're expensive and the surgery has risks, so many bilaterally deaf people have only one implant.

In the United States, CIs are approved starting at 9 months old, but not any younger. (This is a problem for auditory development--although CI are often billed as a "cure" or "complete treatment" to deafness, the reality is that even bilateral CI users who received speech and auditory therapy from the moment their devices were programmed still lag behind hearing peers in auditory development, because they are deaf. But that's part of a larger conversation regarding deaf development and audism.)

CIs have a small disc that magnetically attaches to the skull near the implant site. That disc transmits the sound through the bone, which is then transmitted to the auditory nerve. Usually, the disc is connected to a wire, which runs to a behind-the-ear processor piece. CIs have a couple different types, just like hearing aids. I'll run through them pretty quickly.

1. "Button" CI.

These are fairly new. They only have the magnetic disc; all the processors and microphones are inside it. They're less visible, but less powerful.

2. Behind the ear microphone.

The BTE component contains the microphones and processors. There is a hook to keep it in place on the ear, but no part of the CI goes into the ear canal. These have similar directional power to BTE hearing aids.

3. In-ear microphone.

The processors are on a behind-the-ear component, but they receive signal from a microphone positioned at the opening of the ear canal. These give the best directional sound filtering, since they receive the auditory input from the same place as a hearing person, often with the benefits of the shape of the outer ear.

4. Mixed type CI + hearing aid.

These are also very new! Previous CI techniques, and many surgeons today, destroy residual hearing, so when the CI processor is disconnected, the user receives no auditory input, even if they had some before getting a CI. However, some new techniques can preserve residual hearing, and the cochlear implant can be combined with a hearing aid. This device looks like a BTE hearing aid with either a mold or power dome, but also connected by a wire to the magnetic disc of a CI.

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What type of CI a person has depends on the technology when they were implanted, what sound quality they want, or what they can afford.

The sound from CIs don't match how hearing people hear things. CI have way fewer neural connections than the cochlea has. Bilateral CI is often more effective for oralism than unilateral, but even then, CIs do not replicate natural hearing.

A CI can be implanted at any age, although it's most "effective" in infancy or adults with new-onset hearing loss, rather than people who have grown up d/Deaf. Getting a CI in adulthood is a very personal choice and can have a lot of meaning for a Deaf person.

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Gene Therapy:

[Plain Text: Gene Therapy]

This post has gone on long enough, and this isn't a hearing assistive device, but it is something to consider in a sci-fi or post-modern setting, and something we (the Deaf community) have to deal with right now.

There are currently new therapies (around 3 years in trial) that target OTOF mutations that cause severe to profound congenital deafness. OTOF mutations cause the loss of a protein that turns cilia movement in the cochlea into neural signals. The gene therapy introduces the gene that codes for this protein into the inner ear.

A small study on around 20 children, teens, and young adults with profound hearing loss (>100 dB) saw hearing curves change to 56 dB +/- 30 dB. I couldn't get the raw data because I couldn't access the study, but that means the average participant is still moderately hard of hearing and still needs hearing aids and accommodations. Depending on the metrics for calculating that error, there was likely at least one participant who remained severely to profoundly deaf after the gene therapy, and no participants became medically hearing.

We still have no data on if this gene therapy lasts forever or what kind of side effects it has. It also only works for a specific class of OTOF mutations, which account for many cases of congenital genetic deafness, but not all. Every single study on the gene therapy is produced by one company. This technology has not yet been peer-reviewed or tested for long enough. Nevertheless, hearing people are treating this as a cure, that the Deaf community doesn't want.

If a deaf person wants access to a technology like this, that is again their choice. Forcing this onto infants and children without autonomy or the ability to make an informed decision is horrible. The push to "cure" deafness goes hand-in-hand with the destruction of Deaf culture. It is eugenics. If you're going to include gene therapy or some other magical "fix" to deafness in your story, think about that.

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Keep writing, and keep sending in your questions!