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   Rehabilitation Engineering Research Center
   on Hearing Enhancement

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Dr. Ross on Hearing Loss

Invisible Extended Wear Hearing Aids

by Mark Ross, Ph.D.

Many years ago, when I was “issued” my first hearing aid at Walter Reed Army Hospital, I was informed that I was one of the “lucky” ones; compared to a previous generation of hearing aids the one just given to me was “small and convenient.” The body worn aid  was about the size of a pack of cigarettes and could operate two or three days with its “A” battery. (A second battery, the “B” battery, could last for two weeks or so.) To my way of thinking, and given the standards of the day, the hearing aid could indeed be considered small and convenient. Little did I know how much public perceptions of size and convenience would change in the ensuing years; an aid’s visibility, rather than its performance, seems to have become a dominating hearing aid design goal. Recent years have seen the hearing aid industry providing us with progressively tinier hearing aids, to the point where an entire hearing aid can now be placed far down in the ear canal or surgically embedded in the middle ear. Two such hearing instruments will be described below.

The first one, the Lyric, was introduced to the public - with a great deal of fanfare - about three years ago. Its most prominently advertised features are its invisibility and wearing convenience; once properly fit (an important caveat) it is designed to be worn twenty-four hours a day during all activities, except perhaps while swimming. The idea is to wear it and forget it. It is placed far down in the bony portion of the ear canal, with the receiver (the speaker) located about 4 millimeters from the eardrum. It is this placement, close to the eardrum, that produces one of the major acoustical advantages claimed for the aid; the other is that it limits the “occlusion” effect (where one’s own voice sounds as if it is coming from a barrel). Another possible acoustical advantage derives from the microphone being recessed about 4 millimeters into the canal , making it deep enough to be invisible but also permitting the ear itself to acoustically shape the input sounds (for example, by emphasizing high frequency sounds – which the external ear and ear canal are designed to do).  In clinical studies conducted by the company, users did subjectively prefer the Lyric to their own hearing aids; although objective test scores were not statistically better, they were no worse either.

The aid is a digitally programmable, analog hearing instrument. Although not as acoustically flexible as a fully digital hearing aid, the device does permit the modification of up to five electroacoustic dimensions, in accordance with personal needs. Because of its location within the ear canal, some hearing aid features - such as directional microphones, which ordinarily require digital signal processing - can, to some extent, be achieved naturally. And because less amplification is required when a receiver (speaker) is placed close to the eardrum, the onset of feedback is less likely to occur. Indeed, from an acoustic point of view, this placement produces the key acoustic advantage of the aid. It’s like having someone talk right into your ear rather than from four or eight feet away; less energy is required to achieve the same sound loudness. However, because it is an analog aid, digital signal noise suppression circuits cannot be included; also, because of its diminutive size, the aid does not contain a telephone coil, thus precluding the aid’s use as an assistive listening device. 

The Lyric is a disposable hearing aid. Batteries cannot be changed. Once the battery is drained, the hearing aid will not work and has to be discarded and replaced with an entirely new instrument. Since it takes special training and skill to place a hearing aid that far down into the ear canal, the user must return to the dispensing audiologist for a brief re-fit appointment. The company states that the battery is designed to last “up to four months” when worn 24/7; on average, again according to the company, users can expect five or six re-fits a year. In addition, the aids are not sold; rather, a prospective user must   purchase a “subscription” for either one or two years.  A year’s subscription costs about $3200 for a pair of Lyric hearing aids. Over a five year period (the life-span of a typical digital hearing aid), the total cost of the Lyric will come to about fifteen or sixteen thousand dollars.  

Because of unique personal ear geometry, only about 50% of people with a hearing loss can be fit with the Lyric hearing aid. Some ears canals are too narrow, or short, or manifest other quirks that make use of an extended wear hearing aid inadvisable. Audiologists dispensing the Lyric receive special training in determining candidacy as well as in fitting the hearing aid. Once the aid is in place, users can adjust the volume and setting remotely with an adjustment tool. They can also remove the aid by using a special tool, but its re-insertion must be done by the dispensing audiologist.

Recently a clone of the Lyric has been introduced, termed the “WOW!” The same parent company manages both aids, although each operates its own dispensing network. From what I have been able to learn, their only difference lies in the dispensing model they practice. Physically and electroacoustically they are the same. Unlike the Lyric, which requires a subscription, the WOW! aids are purchased by the user at a cost of $425 each or $850 for a binaural fitting. If four sets of aids are required in a year, the total cost would then come to $3400, about the same as a year’s subscription to the Lyric.  The rationale offered by the WOW! Company is that some people may not be full time users of  hearing aids and with this model they would only pay for what they use.

There seems little doubt but that the major appeal of the aid (treating the Lyric and the WOW! as one aid) is its invisibility. Nowadays, it seems that the marketing appeals of most hearing aids emphasize their “cosmetic” appeal (a code word for invisibility). For a more or less “conventional” hearing aid, the winner in this competitive race does seem to be the Lyric (winning by a by a nose or a few millimeters). There are people for whom invisibility is the prime consideration when it comes to acquiring a hearing aid; this is a   personal choice that people make. They would rather wear no aid at all than one that is visible; for them, the Lyric is a viable option. They should, however, be aware of some downsides.

Over the life-span of a conventional hearing aid, the cost of an extended wear hearing aid will easily surpass it by a factor of two or three.  Each time a battery dies, the Lyric user will have to travel to the dispensing audiologist to get a replacement. The convenience in wearing the aid has to be balanced by the inconvenience of obtaining a re-fit, as well as the issues arising from the period that they are going to be deprived of amplification. Finally, it seems that generally accepted hearing aid selection techniques are not being   followed while fitting the Lyric. For example, neither real-ear measures nor standardized electroacoustic analyses can easily be done. The only suggested test that can provide some information about a hearing aid’s electroacoustic response is the comparison of unaided versus aided pure-tone thresholds as measured via a loudspeaker in a sound-treated room (a test that dates to WW II).  Useful, to be sure, but available procedures have come a long way since then.  

The most recent addition to the ranks of invisible, extended wear hearing devices is the Esteem, which received final approval from the FDA in early 2010. Conceptually, this is a fascinating instrument, one that employs the structures of the middle ear to deliver intensified sound vibrations to the inner ear. In a normal ear, the eardrum converts incoming sounds to vibrations that are transmitted through the three tiny bones in the middle ear; the last of these three bones (called “the stapes”) is what finally sets the cochlear fluids into motion (triggering  the neural response). The Esteem piggy-backs on the normal function of the eardrum while intensifying the vibratory motions delivered to the stapes. Basically, this hearing device is a middle ear (rather than a cochlear) implant, one that uses the person’s eardrum as a microphone and the stapes as the receiver.

The first stage in fitting an Esteem is similar to that followed with a cochlear implant. A sound processor is surgically implanted under a patch of skin behind the ear. It looks to be about the same size and dimensions as a cochlear implant. This processor is connected to two other components implanted in the middle ear. The first is a sensor which is attached to the malleus (the first of the three middle ear bones). The second is a driver which is connected to the stapes. The physical connection between the middle bone (the incus) and the stapes is severed. The sensor picks up the vibrations of the eardrum and converts these vibrations to electrical signals. These signals are then transmitted via a wire connection to the implanted processor. The processor amplifies and personalizes these electrical signals and transmits them to the driver, resulting in intensified vibratory motions of the stapes. Functionally what is happening is that the incoming sound signals are being amplified to make them more audible to the listener. 

The Esteem is undoubtedly an extended wear, convenient device. It is completely invisible and can be used in any and all activities, including swimming (but not below 30 feet). This is a sophisticated electronic device, one that requires the services of a skilled surgeon to successfully implant. A user has some control over the signal via a remote control. This is used to adjust the volume, select one of three listening programs, or turn the device on or off.  Battery life is said to extend from three to nine years; battery changes requires a short repeat visit to the surgeon.  The listening research conducted by the company reports generally higher scores on a word discrimination test compared to the subject’s previous hearing aid, as well as more favorable subjective judgments. As far as I know, no independent listening research has yet been conducted with the Esteem.

At $30,000 per device (including device and surgery) the device is not for the faint of heart or the financially challenged. Particularly, in my opinion, since optimum function would require two units, one for each ear. (Otherwise, the person would be a one-ear listener, with all the attendant disadvantages of a unilateral hearing loss.) As in most any surgery there are some possible side-effects; these include possible facial paralysis (7%) and taste disturbances (42%); most of these are reported to clear up within the first year. The company’s website (envoymedical.com) includes many raving testimonials, which is a traditional marketing approach with just about any device. But what I found particularly grating was the unwarranted bad mouthing of conventional hearing aids. It was not only unpleasant and unfair, but inaccurate and uninformed. 

Audiologically, this device does present some unique challenges. Esteem recipients probably display a range of sensori-neural hearing losses. However, the user can select only one of three possible listening programs (although the fitting audiologist may have more options during the initial programming of the device). We do not know if one of these three options would be the most appropriate for someone with a specific audiogram shape. While the theoretical advantages of using normal anatomical structures - the eardrum and stapes - in the sound transmission process seem evident, the signals are still being delivered to a pathological inner ear (the cochlea).  Once a decision is made to use the Esteem, a user is committed; the use of conventional hearing aids would not be possible. While the Esteem is an impressive and creative development, in my judgment the jury is still out regarding its overall benefits compared to a pair of modern digital hearing aids.

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Last modified: 07/01/2013

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