Hearing Aids
Timothy C. Hain, MD
Last modified: 8/08
What Treatments are Available?
For many hearing disorders, there is no actual available cure. However, there are assistive devices and some promising new treatments that allow patients to manage their hearing disorders. While regeneration of inner ear hair cells is presently not possible, as medicine advances, it seems very likely that a method will be found to regrow inner ear hair cells in the future.
Hearing Aids
Hearing aids are electrical devices that assist in optimizing perception of speech or other sounds. Most hearing aids are designed for hearing impaired individuals, of which there are approximately 28 million in the United States.
A basic hearing aid consists of a microphone, amplifier, volume control, battery and receiver. A straightforward approach is simply to amplify sound coming in. This approach often fails due to a limited range of usable volumes (it might be either too loud or too soft). More recent designs use compression circuitry to represent the full range of sounds within the range tolerated by the wearer. Digital hearing aids and programmable hearing aids offer more flexibility in the processing. It is often desirable to have a hearing aid behave differently in a busy room than when speaking one-on-one. This is possible with a programmable aid.
Who Needs a Hearing Aid?
In essence, you need a hearing aid if you have hearing problems and the cost/benefit ratio of a particular aid is reasonable. An "ideal" hearing aid candidate is someone with a mild or moderate bilateral hearing loss, who has experienced a noticeable communication handicap. Many individuals who have good hearing on one side can adjust reasonably well to any degree of hearing loss on the other side, and for this reason, most people that get hearing aids have bilateral decreases in hearing.
Hearing aids are not indicated for an ear with minor hearing loss, and are also not very useful in an ear with profound hearing loss. In other words, hearing aids are usually most appreciated in people with mild to moderate hearing loss on both sides. Sometimes an "assistive device" can be used -- this is a small personal amplifier. Amplifiers are also available for telephones and TVs. The telephone company may supply you with one for your telephone at little or no charge. You should be able to find many vendors by using "Google" to search for "assistive devices for hearing". Some low-end assistive devices sell for as little as $50.
Be sure that you need a hearing aid. It is estimated that two-thirds of all hearing aids go unworn (or into the drawer).
What Tests are Necessary Before Selecting a Hearing Aid?
An audiometric evaluation should be performed to determine the type of hearing loss (sensorineural, conductive or central), the degree, and the frequency slope. The evaluation should also be able to predict the amount of benefit that an aid will provide, in terms of speech comprehension.
In selecting a hearing aid, a special appointment called a "fitting" is usually needed. The fitting maps out how much amplification is needed, the uncomfortable loudness level, (ULC) (which is the maximum tolerable loudness) and the most comfortable listening level (MCL). The dynamic range is defined as ULC minus MCL. Fitting also involves selection of the style of hearing aid, and usually selection or fabrication of an ear-mold. Recently, the process has gotten a little easier as off-the-shelf aids (for example, the Songbird) seem to provide as good results as the more arduous process. Social service agencies are often involved with hearing aid dispensing.
An otologic evaluation should also be performed to determines whether medical or surgical treatment is possible (for example, ear wax removal). Medical clearance is advisable before purchasing a hearing aid.
Types of Hearing Aids
There are many types of hearing aids available in the market. Selecting a hearing aid depends on the specific hearing loss, the cosmetic appearance, and the amount one wishes to spend. Hearing aids can be categorized by technology and by style (size and appearance). The different technologies are available in the different styles.
Technologies
- Analog. There are several circuits.
- Linear peak clipper (least favored in VA study, Larson et al, 2000)
- Compression limiter (preferred in VA study)
- Wide dynamic range compressor (second-best in VA study)
- Simple programmable. Longer fitting time and follow-up.
- Complex programmable.
- Digital. Flexible but expensive. There are presently about 14 digital aids
on the market.
- Implantable aids. Somewhat better performance can be obtained by implanting
the hearing aid.
New advances that may be beneficial include intra-aural silicone directional microphones that allow the wearer to better understand sounds from multiple directions (Miles, 2006; Ricketts, 2005; Bentler, 2005) and bone anchored hearing aids (BAHA). BAHA percutaneously transmit sound through the skull (Snik, 2004) and may be more effective than traditional aids in some patients with conductive hearing loss (Hol, 2005). An implantable ossicular stimulator has proven effective in clinical trials (Jenkins, 2007 and 2004).
Style
- Assistive listening devices. A large variety of devices are available at much lower cost than hearing aids. Some of these are free. Telephone companies provide free amplifiers and ringers if patients present a physician or audiologist release. Hotels provide telephone amplifiers in 10 percent of rooms. Examples are devices that flash lights when the telephone rings, vibration devices when the doorbell sounds, flashing smoke alarms, television amplifiers, etc.
- Behind the ear (BTE). Cheapest, easiest to adjust, less feedback than other devices. Fairly visible. Most powerful. Fewest number of problems with wax or infections.
- In the ear (ITE). Low visibility; harder to put in and adjust.
- In the canal (ITC). Very low visibility. Clearer than Assistive listening devices and BTE. Lower power. Patients with tremor or poor eyesight are not good candidates.
- Completely in the canal (CIC). Cannot be seen. Requires tight fit. Hard to adjust and remove. Clearer than assistive listening devices and BTE. Patients with tremor or poor eyesight are not good candidates.
In addition to technology and style, one must decide between wearing a hearing aid in one ear (monaural) or wearing a hearing aid in both ears ( binaural). Binaural amplification is generally better than monaural because it minimizes the impact of "head shadow" drop off, improves sound localization, and widens the dynamic range. However, having two hearing aids costs twice as much, and it is more trouble to keep two hearing aids maintained. Patients who report the greatest benefit from binaural aids are those with more severe degrees of hearing impairment and those with more demanding and dynamic listening environments (such as crowded rooms) (Noble, 2006). Bicross hearing aids are also available, in which one side "pipes" sound to other side, where hearing is better. Most hearing aid users are unenthusiastic about bicross aids.
Cost
There are numerous brands and variants. In general, smaller devices, such as the CIC devices mentioned above, are more expensive, and newer/more complex circuitry is also more expensive. Compression circuitry in analog aides is more expensive (but definitely a good idea). Greater user control is also usually more expensive. Binaural aids are always better when there is usable hearing in both ears.
Many states have a 30 day tryout period, which is basically a legally mandated money-back guarantee for the hearing aid device itself. The dispenser is allowed to keep a fee for their services during the trial. As historically 2 out of every 3 hearing aids are not worn (at least not worn often), and hearing aids are generally not covered by insurance and typically costs in the thousands of dollars, we recommend that you think about this carefully.
Cochlear Implants
An exciting recent development is an ability to provide hearing to some bilaterally deafened individuals through implantation of a device that directly stimulates the hearing nerve (spiral ganglion). Although this device is not generally considered as a hearing aid, it performs the same purpose for individuals with severe hearing impairment involving both ears. At this writing, 8/08, there are several companies that make implants: Clarion and Nucleus and Med El Corp. For more details, see the Clarion web site.
Most neurotologists are able to perform this procedure. Cochlear implants do not completely substitute for a normally hearing ear, and at very best, may allow someone who was previously totally deaf to understand conversation on a telephone. Cochlear implant packages, including the device, surgery, and rehabilitation are much more expensive than hearing aids (roughly $45,000), but when one is indicated, they are generally covered by insurance, unlike the situation with hearing aids. A patient-contributed history is found here. Further information about cochlear implants can be found at the following sites:
Combined electrical and acoustic stimulation (EAS) uses a cochlear implant in combination with a hearing aid, and may be beneficial in some patients (Kiefer, 2005).
Regeneration of Inner Ear Hair Cells
Many processes that affect the inner ear kill hair cells, which are the main sensory part of the ear. While it would seem reasonable that hair cells should be replaced when they are lost, this seems to be somewhat species specific. Hair cells of birds, both auditory and vestibular, regenerate but hair cells of humans are generally felt to not regenerate. (Goode et al, 1999; Carey et al, 1996).
Research Studies on Hearing Aids and Regeneration
At the American Hearing Research Foundation (AHRF), we have funded considerable basic research on hearing aid technology as well as basic research related to hair cell regeneration in the past. Click here if you would you would like more information about contributing to the AHRF's efforts.
References
- Bentler RA. Effectiveness of directional microphones and noise reduction schemes in hearing aids: a systematic review of the evidence. J Am Acad Aud. 16(7):473-84, 2005.
- Carey JP, Fuchs, AF, Rubel E. Hair cell regeneration and recovery of the vestibuloocular reflex in the avian vestibular system. J.Neurophysiol 76:3301-3312, 1996.
- Demystifying Hearing-Aid Technology. Audio-digest (several authors), April 15, 1998. Vol 31, #8
- Goode CT, Carey JP, Fuchs AF, Rubel EW. Recovery of the vestibulocolic reflex after aminoglycoside ototoxicity in domestic chicken. J. Neurophysiol 81(3):1025:1099
- Hol MK, Snik AF, et al. Does the bone-anchored hearing aid have a complimentary effect on audiological and subjective outcomes in patients with unilateral conductive hearing loss? Aud Neur Oto. 10(3):159-68, 2005.
- Jenkins HA, Atkins JS et al. US Phase I preliminary results of use of the Otologics MET Fully-Implantable Ossicular Stimulator. Otolaryn Head & neck Surg. 137(2):206-12, 2007.
- Jenkins HA, Niparko JK et al. Otologics Middle Ear Transducer Ossicular Stimulator: performance results with varying degree of sensorineural hearing loss. Acta Oto-Laryngologica. 124(4):391-4, 2004.
- Kiefer J, Pok M et al. Combined electric and acoustic stimulation of the auditory system: results of a clinical study. Aud Neur Oto. 10(3):134-44, 2005.
- Kim HH, Barrs DM. Hearing aids: a review of what's new. Otolaryng Head & Neck Surg. 134(6):1043-50, 2006.
- Larson VD and others. Efficacy of 3 commonly used hearing aid circuits. JAMA 2000:284. 1806-1813.
- Miles RN, Hoy RR. The development of a biologically-inspired directional microphone for hearing aids. Aud Neuro-Oto. 11(2):86-94, 2006.
- Noble W. Bilateral hearing aids: a review of self-reports of benefit in comparison with unilateral fitting. Int J Aud. 45 Suppl 1:S63-71, 2006.
- Rickets TA. Directional hearing aids: then and now. J Rehab Rsch Dev. 42(4 Suppl 2): 133-44, 2005.
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