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LESSON 179

Hearing aid styles

Year 3
Fall semester
Hearing Aids I
Amplification basics
Duration: 10:15

How do behind-the-ear, receiver-in-canal and in-the-ear hearing aids differ? In this lesson we cover the BTE, RIC, ITE, ITC and CIC styles, open fitting and the occlusion effect, and the role of degree of loss, ear canal and dexterity in choosing a style.

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Hello, and welcome to the AIHEAR Audiology Academy.
In this lesson we will get to know the behind-the-ear and in-the-ear hearing aid styles one by one.
Then we will see how degree of loss, the ear canal and dexterity shape the choice of style.
The first style is the behind-the-ear hearing aid, known as BTE.
In a BTE, the microphone, processor and receiver are all in the case that sits behind the pinna.
Sound travels through an earhook and tube to a custom earmold, and from there into the ear canal.
The large case fits a powerful receiver and a large battery, so it suits a wide range of losses, from mild to profound.
It is often chosen for children, because as the ear grows only the earmold is replaced, not the aid.
The earmold can be made of soft material, which makes it safe to use in a child's ear.
It also connects easily to the remote microphone systems used in schools.
Thin-tube BTE models use a thin tube and a dome instead of a thick tube and earmold.
The second style is the receiver-in-canal hearing aid, or RIC.
In a RIC the case is still behind the ear, but the receiver sits inside the ear canal on a thin wire.
Because the receiver is out of the case, the case is smaller and the aid is less visible.
The tip in the ear canal may be a vented silicone dome or a custom earmold.
Because the microphone and receiver are farther apart, more gain can be given in an open fitting without feedback.
With receivers of different power, it can be used for many losses, from mild to severe.
Its drawback is that the receiver is in direct contact with wax and moisture in the canal, so the wax filter must be changed regularly.
The third group is the in-the-ear hearing aids, or ITE.
All the parts are placed inside a custom shell made from an impression of the person's ear.
A full-shell ITE fills the bowl of the pinna, the concha; half-shell models are smaller.
Being relatively large, it is easier to handle, insert and change batteries than smaller models.
Extra features like a telecoil, two microphones and buttons can fit; it is usually used for mild to severe losses.
Because it blocks more of the ear canal, the person may hear their own voice as muffled; this is the occlusion effect.
Because the microphone sits in the concha, the natural acoustic effect of the pinna is partly retained.
The in-the-canal hearing aid, or ITC, sits at the entrance of the ear canal and in a small part of the concha.
The completely-in-canal aid, or CIC, sits deeper and has a small cord for removal.
These two styles are the least visible options cosmetically.
Models that sit even deeper in the canal and are almost invisible are called invisible-in-canal, or IIC.
In a CIC the microphone stays at the canal entrance, so it benefits from the natural directional and resonance effects of the pinna.
On the other hand, the battery is small, and a telecoil or directional microphone may not fit in the shell.
In addition, these styles can only be made if the ear canal is wide and straight enough.
Now let us put the styles side by side; these ranges are general trends, not strict limits.
With a powerful receiver and earmold, BTE covers the widest range, up to profound losses.
RIC is commonly used from mild to severe losses, thanks to receivers of different power.
ITE is the largest of the in-the-ear styles and can be used from mild to severe losses.
Because of its small shell, ITC is usually suited to losses from mild to moderately severe.
The general range is similar for CIC; its output is often limited by feedback and shell size.
As the aid gets smaller, visibility drops, but so do power, number of features and ease of use.
A decision as important as the style is how much of the ear canal to close.
An open fitting uses a vented dome or a widely vented tip, and the ear canal stays largely open.
Low-frequency sounds then enter the ear naturally, and the person's own voice sounds more natural.
So the occlusion effect is kept to a minimum.
In a closed fitting, an earmold or closed dome blocks the ear canal.
This reduces sound leakage and allows more gain, especially at low frequencies.
On the other hand, when the cartilaginous part of the canal is closed, the person may hear their own voice as muffled and echoey.
So a closed fitting is preferred mainly for people who also have a marked loss at low frequencies.
In this example, both ears show a similar loss that slopes toward the high frequencies.
Thresholds are near normal at low frequencies, and between moderate and severe from 2000 Hz upward.
This person may not need extra gain at low frequencies, and a closed tip could make their own voice sound muffled.
So a pattern like this is a common example where an open-fit RIC or a thin-tube BTE is considered.
But the decision is not made from the audiogram alone; the ear canal, dexterity and the person's expectations also count.
Bone conduction is needed to determine the type of loss; in this example we focus only on the configuration.
The first question in choosing a style is the gain and output needed, set by the degree and configuration of the loss.
With a profound loss, a small in-the-canal aid may not deliver the required power without feedback.
The second factor is the ear canal: a narrow, very curved or very waxy canal makes small in-the-ear models difficult.
The third factor is dexterity and vision; inserting a small aid and changing a tiny battery is not easy for everyone.
In such cases, a larger case or a rechargeable model can make use easier.
If a telecoil for the phone or a directional microphone for noise is needed, choose a style that can hold these features.
Finally, the person's cosmetic expectations, work and daily life are also part of the decision.
In short, choosing a style is a shared decision made with the person; the weight of each factor varies from person to person.
Behind-the-ear aids are usually preferred for children.
As the ear canal grows, only the earmold is replaced; the aid itself can be used for years.
A battery door that can be locked so the child cannot open it is also an important safety feature.
In older adults, fine dexterity and vision may decline, so very small models can be challenging.
Rechargeable aids remove the battery-changing step and can make use easier.
Training a caregiver to insert and clean the aid also improves adherence.
Marking the right aid red and the left aid blue is another practical detail that prevents mix-ups.
A tip from the field: always examine the ear canal with an otoscope before taking an impression for an in-the-ear aid or earmold.
During the impression, a block is placed in the ear canal to stop the material from reaching the tympanic membrane.
If there is ear discharge, heavy wax or a suspected perforation, no impression is taken and medical assessment is requested first.
Also remember that in people with frequent ear discharge, fittings that block the ear canal can cause problems.
A good impression is the first step toward a comfortable fitting without feedback.
We saw that in behind-the-ear styles the case sits behind the pinna, and in a RIC the receiver moves into the canal.
In-the-ear styles get smaller from ITE to CIC; along with visibility, power and features also decrease.
Open fitting reduces the occlusion effect in people whose low frequencies are near normal.
The style is chosen together with the person, based on degree of loss, ear canal, dexterity and needs.
Test yourself: for a person whose low frequencies are near normal, which option reduces the occlusion effect most?
The correct answer is B: an open-fit RIC.
Because the ear canal stays open, low-frequency sounds and the person's own voice pass through naturally.
In the next lesson we will see how a hearing aid's gain, maximum output and frequency response are measured.
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Prerequisites

LESSON 178 How do hearing aids work?

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