Factors to Consider When Choosing a Hearing Aid Style1

If your outer ear is small or deformed, you may be unable to wear a BTE.

If your ear canal is small or deformed, you may be unable to wear a CIC or an ITC.

If the “bowl” of your outer ear is shallow, you may be unable to wear a full shell ITE.

If your vision or manual dexterity are limited, you may have trouble wearing a CIC or an ITC (tiny hearing aids and tiny batteries require adequate vision and nimble fingers—or assistance from someone else).

If your ears produce an unusual amount of wax, you may be unable to wear a CIC or ITC.

If you have a draining ear, you may need a large vent or a BTE with an open canal fitting (so that air can enter your ear canal).

If you have a high-frequency hearing loss and normal or nearly normal low-frequency hearing, you may be most comfortable with a large vent or a BTE with an open canal fitting (this should allow you to hear lowfrequency sounds naturally and reduce or prevent the occlusion effect).

If you have a severe or profound hearing loss, you may need the power available only in a BTE; however, an open canal fitting may be impossible because of feedback.

If you need technical features that increase comfort and improve understanding in noisy situations, you may need a larger hearing aid (BTE or ITE).

If you’re making a decision on the basis of how the aids look, you may find that an open canal fitting with a mini-BTE is less conspicuous than other styles—take a look!

SPECIAL TYPES OF HEARING AIDS

Wireless CROS or BICROS

The acronym CROS stands for contralateral routing of the signal, which is a special hearing aid arrangement sometimes used by listeners who have very poor hearing (or very poor speech perception ability; see Chapter 4) in one ear and normal hearing in the other. Sometimes hearing or speech perception is so poor that it’s unusable, even with a hearing aid. With a CROS system, a microphone worn on the bad ear (in what looks like a conventional hearing aid) picks up sounds and transmits them (by FM radio waves—no wires are necessary) to a receiver worn on the good ear (in what also looks like a conventional hearing aid). This allows the listener to hear sounds on her bad side that would otherwise be missed. Having a microphone on the “dead ear” also can improve the listener’s ability to localize the source of sounds.

A BICROS system (bilateral CROS) is similar, but it’s used when the hearing in one ear is unusable and the hearing in the other ear is not

normal. This is actually the more common arrangement. A microphone worn on the bad ear picks up sounds and transmits them to the better ear. The hearing aid on the better ear amplifies sounds coming from both sides and delivers them to the better ear. Traditionally, wireless CROS and BICROS systems have been housed in BTEs. They’re now available in ITEs as well. A variety of digital signal processing features (see later discussion) can be incorporated.

My Dad

My dad has suffered from Meni´ere’s` disease for about 25 years (see Chapter 5). A few years ago, the hearing and tinnitus in his left ear became worse. Because I thought wearing hearing aids might bring relief from the tinnitus (see Chapter 6), and because he seemed to be having so much difficulty hearing (his right ear also had some hearing loss, probably because of age; see Chapter 5), I encouraged him to try hearing aids. The hearing in his right ear was still fairly good at that time; therefore his audiologist recommended a hearing aid for the left ear only. Not long after he bought the aid, he had a particularly bad episode (of Meni´ere’s` disease) and lost virtually all ability to understand speech in the left ear. A hearing aid was no longer useful in that ear. Fortunately, because it was a digital aid, his audiologist was able to reprogram it for use in his right ear (on which he now had to depend).

Later, I suggested that my dad try using a BICROS hearing aid arrangement. He wore what appeared to be a conventional BTE hearing aid containing a microphone and transmitter on his left ear. Sounds picked up on his left side were transmitted (wirelessly) to the hearing aid on his right ear. On his right ear, he wore a conventional BTE hearing aid that picked up sounds from his right side and also received the signals transmitted from his left side. It amplified signals from both sides and delivered them to the right ear, allowing him to pick up sounds on his left side that he would otherwise have missed and giving him a better sense of where sounds were coming from. He wore this arrangement for several years and thought that it was helpful in some situations but not so helpful in others.

Disposable, Deep-fitting, Extended-wear Devices

In the future, disposable, extended-wear devices that fit deep within the ear canal could become more widely available. The disposable device is placed extremely close to the eardrum by an ENT physician and worn continually for about 120 days, or until the battery ceases to function. The device is completely invisible and said to offer improved sound quality. With its initial release, patients paid about $1,450 to $2,000 per ear, per year.

Middle Ear Implants

A middle ear implant may be an option for a person who is unable to tolerate conventional hearing aids and has too much hearing to be a candidate for a cochlear implant (see Chapter 8). With this type of hearing device, a tiny electromagnetic coil is surgically attached to one of the bones within the middle ear (the incus), and a receiver is implanted under the skin behind the outer ear. An external processor containing a microphone, amplifier, and battery is held over the implanted receiver by a magnet. The external processor picks up sounds from the environment and transmits a representation of them across the skin to the implanted receiver. The receiver sends the signals through a conductor to the electromagnet implanted on the incus. Signals sent to the incus cause the ossicular chain to move, and movement of the ossicular chain transmits energy to the cochlea in the natural manner (see Chapter 3).

Candidates for middle ear implants usually have a sensorineural hearing loss, a normally functioning middle ear, and an unsuccessful history with conventional hearing aids. Using a middle ear implant eliminates the need to wear a hearing aid or earmold in the ear canal, which in turn eliminates problems such as discomfort, the occlusion effect, allergic skin reactions, feedback, and wax damage to the hearing aid. However, surgery is more expensive than buying conventional hearing aids and carries more risks. In the future, it’s possible that middle ear implants could be totally implantable and therefore invisible (with the microphone implanted in the ear canal).

Bone Conduction Devices

If you’ve had a hearing evaluation, the audiologist may have tested your hearing by bone conduction (see Chapter 4). This is done by placing a small box against the bony bump behind your ear (the box would have been attached to a metal band that stretched across your head). A traditional bone conduction hearing aid is similar to that device—awkward and cumbersome to wear all the time. A bone-anchored hearing aid is an implantable device that allows the listener to hear by bone conduction without the inconvenience of a traditional bone conduction hearing aid. It’s more comfortable, and the sound quality is better, partly because the device stays in place.

Unlike a middle ear implant, which requires a normally functioning middle ear, this type of hearing aid is typically used by listeners who have conductive or mixed hearing loss. Bone conduction hearing aids have traditionally been used by people born without ear canals or with small, misshapen ears that can’t support conventional hearing aids, or by people who have chronic middle ear disease that’s aggravated by wearing a hearing aid or earmold in the ear canal (for example, people with draining ears).

With a bone-anchored hearing aid, a titanium post is implanted in the bone behind the outer ear, and the post becomes integrated into the bone as it heals. When healing is complete, a hearing aid is attached to the post with an abutment. Sounds processed by the hearing aid cause the implanted post

Figure 7.7. A Bone-anchored Hearing Aid. (Courtesy of Cochlear Americas.)

to (imperceptibly) vibrate the bones of the skull, stimulating both cochleae by bone conduction (see Chapter 4). The ear canal and middle ear (where the problem lies) are bypassed. As with a middle ear implant, the ear canal remains completely open.

The bone-anchored hearing aid also works for people who have singlesided deafness or one ear that can’t be aided (in this case, it would be an alternative to a CROS hearing aid system). When hearing is stimulated by bone conduction, the bones of the skull vibrate, and the fluids inside both cochleae are stimulated (see Chapter 4). That means sounds picked up by a microphone on the listener’s “bad” side reach both cochleae (including the one with better hearing) by bone conduction.

My Dad

A bone-anchored hearing aid might be a good solution for my dad, but he won’t consider the surgery.

Other nontraditional bone conduction options are available for people who have single-sided deafness. In one case, a microphone worn on the nonhearing ear converts sounds picked up on the bad side into electrical signals. However, instead of amplifying them and converting them back into sound (like a conventional hearing aid), the electrical signals drive a small “vibrator” that sits in the canal of the nonhearing ear where it makes contact with the bones of the ear canal. When it vibrates, sounds are transferred by the bones of the skull to both cochleae (including the one with better hearing). Because the device is not implanted, surgery is unnecessary.