Hearing loss

Definition

Hearing loss is any degree of impairment of the ability to apprehend sound.

Description

Sound can be measured accurately. The term decibel (dB) is a measure of loudness and refers to a unit for expressing the relative intensity of sound on a scale from zero, for a nearly imperceptible sound, to 130, which is the level at which sound causes pain in the average person. A drop of more than 10 dB in the level of sound a person can hear is significant.

Sound travels as waves through a medium like air or water. These waves are collected by the external ear and cause the tympanic membrane (eardrum) to vibrate. The chain of ossicles (tiny bones) connected to the eardrum—the incus, malleus, and stapes—carries the vibration to the oval window (an opening to the inner ear), increasing its amplitude 20 times on the way. There, the energy causes a standing wave in the watery liquid (endolymph) inside the organ of Corti. (A standing wave is one that does not move.) The frequency of the sound determines the configuration of the standing wave. Many thousands of tiny nerve fibers detect the highs and lows of the standing wave and transmit their findings to the brain, which interprets the signals as sound.

To summarize, sound energy passes through the air of the external ear, the bones of the middle ear, and the liquid of the inner ear. It is then translated into nerve impulses, sent to the brain through nerves, and understood there as sound. It follows that there are five steps in the hearing process:

• air conduction through the external ear to the eardrum
• bone conduction through the middle ear to the inner ear
• water conduction to the organ of Corti
• nerve conduction into the brain
• interpretation by the brain

Hearing can be interrupted in a variety of ways at each of the five steps.

The external ear canal can be blocked with ear wax, foreign objects, infection, and tumors. Overgrowth of the bone can also narrow the passageway, making blockage and infection more likely. This condition can occur when the ear canal has been flushed with cold water repeatedly for years, as is the case with surfers, for whom the condition called "surfer's ear" is named.

The eardrum is so thin a physician can see through it into the middle ear. It can be ruptured by sharp objects, pressure from an infection in the middle ear, or even a firm cuffing or slapping of the ear. The eardrum is also susceptible to pressure changes during scuba diving.

Several conditions can diminish the mobility of the small bones (ossicles) in the middle ear. Otitis media, an infection in the middle ear, occurs when fluid cannot escape into the throat because the eustachian tube is blocked. The fluid (pus or mucus) that accumulates prevents the ossicles from moving as efficiently as they normally do, thus dampening the sound waves. In a disease called otosclerosis, spongy tissue grows around the bones

of the inner ear. This growth sometimes binds the stapes in the oval window, which interferes with its normal vibration and causes deafness. All the conditions mentioned so far—those that occur in the external and middle ear—are causes of what is known as conductive hearing loss.

The second category, sensory hearing loss, refers to damage to the organ of Corti and the acoustic nerve. Prolonged exposure to loud noise is the leading cause of sensory hearing loss. A million people have this condition, many identified during the military draft and rejected as being unfit for duty. The cause is often believed to be prolonged exposure to rock music. Occupational noise exposure is the other leading cause of noise-induced hearing loss (NIHL) and is ample reason for wearing ear protection on the job.

More unusual, but often undetected, is low-frequency hearing loss. Scientists discovered in 2001 that people with a particular gene mutation gradually lose their abilities to hear low-frequency sounds. Since those people with this type of hearing loss can still distinguish speech, they often remain unaware of the low-frequency changes in their hearing. The scientists believe that the same gene mutations might make some people more susceptible to high-frequency hearing loss, but further study is needed.

One-third of people older than 65 have presbycusis, which is sensory hearing loss due to aging . Both NIHL and presbycusis are primarily loss of the ability to hear high-frequency sounds. In speech, consonants generally have a higher frequency than vowels. Yet in most languages, consonants provide us the clues needed for determining what a person is saying. So these people hear plenty of noise, they just cannot easily make out what it means. They have particular trouble differentiating speech from background noise.

Brain infections such as meningitis , drugs such as the aminoglycoside antibiotics (streptomycin, gentamycin, kanamycin, tobramycin), and Meniere's disease can also cause permanent sensory hearing loss. Meniere's disease combines attacks of hearing loss with attacks of vertigo. The symptoms may occur together or separately. High doses of salicylates such as aspirin and quinine can cause a temporary high-frequency loss, and prolonged high doses can lead to permanent deafness. There is also a hereditary form of sensory deafness and a congenital form most often caused by rubella (German measles ).

Sudden hearing loss of at least 30 dB in less than three days is most commonly caused by cochleitis, a mysterious viral infection.

The final category of hearing loss is neural hearing loss. Permanent neural hearing loss most often results from damage to the acoustic nerve and the parts of the brain that control hearing. Strokes, multiple sclerosis , and acoustic neuromas are all possible causes of neural hearing loss.

Hearing can also be diminished by tinnitus , which is characterized by extra sounds generated by the ear. These sounds are referred to as tinnitus, and can be ringing, blowing, clicking, or anything else that no one but the patient hears. Tinnitus may be caused by loud noises, medication, allergies , or medical conditions—from the same kinds of disorders that can cause diminished hearing.

Diagnosis

Many common causes of hearing loss can be detected through an examination of the ears and nose combined with simple hearing tests performed in the physician's office. An audiogram (a test of hearing at a range of sound frequencies) often concludes the evaluation. These simple tests often produce a diagnosis. If the defect is in the brain or the acoustic nerve, further neurological testing and imaging will be required.

The audiogram has many uses in diagnosing hearing deficits. The pattern of hearing loss across the audible frequencies gives clues to the cause. Several alterations in the testing procedure can give additional information. For example, speech is perceived differently than pure tones. Adequate perception of sound combined with inability to recognize words points to a brain problem rather than a sensory or conductive deficit. Loudness perception is distorted by disease in certain areas but not in others. Acoustic neuromas often distort the perception of loudness.

Treatment

Conductive hearing loss can be treated with alternative therapies that are specific to the particular condition.

Nutritional therapy

The following dietary changes may help improve certain hearing impairment conditions:

• Alleviate accumulated wax in the ear by taking oral supplements with essential fatty acids such as flax oil and omega-3 oil.
• Identify and avoid potential allergenic foods. Children who are allergic to foods have an increased risk of getting chronic ear infections.
• Take nutritional supplements. B-complex vitamins and iron supplements may be helpful in preventing protein deficiency and anemia . These conditions depress immune function and increase the risk of chronic ear infections. Children suffering from frequent ear infections may need supplementation with strong antioxidants such as vitamins A and C, zinc , and bioflavonoids . High-potency multivitamin and mineral supplements should contain most of these helpful nutrients as well as other essential vitamins and minerals.

Herbal therapy

There are several effective herbal treatments for hearing impairments. They include:

• Ginkgo biloba. Ginkgo may be effective in patients with hearing loss who often complain of ringing in the ears.
• Natural antibiotics such as echinacea and goldenseal can help prevent or treat ear infections.
• Certain Chinese herbal combinations can help alleviate tinnitus, ear infections, and chronic sinus infections that can lead to hearing loss.

Homeopathy

Homeopathic therapies may help patients who have sensory hearing loss. An experienced homeopathic physician will prescribe specific remedies based on knowledge of the underlying cause.

Acupuncture

Acupuncture may be able to improve hearing in some patients with sensory-neural deafness. It may be used to improve the circulation of fluids in the head that lead to chronic congestion and noises.

Other therapies

Other therapies that may help improve hearing in some patients include Ayurvedic medicine, craniosacral therapy , and auditory integration training .

Allopathic treatment

Conductive hearing loss can almost always be restored to some degree, if not completely.

• Matter in the ear canal can easily be removed, with a dramatic improvement in hearing.
• Surfer's ear gradually regresses if the patient avoids cold water or uses a special ear plug. In advanced cases, surgeons can grind away the excess bone.
• A middle-ear infection involving fluid is also simple to treat. If medications do not work, fluid may be surgically drained through the eardrum, which heals completely after treatment.
• Traumatically damaged eardrums can be repaired with a tiny skin graft.
• Otosclerosis may be surgically repaired through an operating microscope. In this intricate procedure, tiny artificial parts are substituted for the original ossicles.

Now available for complete conductive hearing loss are bone conduction hearing aids and even devices that can be surgically implanted in the cochlea.

Sensory and neural hearing loss, on the other hand, cannot readily be cured. Fortunately such hearing loss is rarely complete, and hearing aids can fill the deficit. In-the-ear hearing aids can boost the volume of sound by up to 70 dB. (Normal speech is about 60 dB.) Federal law now requires that aids be dispensed only by prescription.

Tinnitus can sometimes be relieved by adding white noise (such as the sound of wind or waves crashing on the shore) to the environment.

Decreased hearing is such a common problem that there are legions of organizations to provide assistance. Special language training, both in lip reading and signing, is available in most regions of the United States, as well as special schools and camps for children.

KEY TERMS

Meniere's disease

—The combination of vertigo and decreased hearing caused by abnormalities in the inner ear.

Prevention

Prompt treatment and attentive follow-up of middle ear infections in children will prevent this cause of conductive hearing loss. Sensory hearing loss as a complication of epidemic disease has been greatly reduced by control of infectious childhood diseases, such as measles. Laws that require protection from loud noise in the workplace have substantially reduced incidences of noise-induced hearing loss. Surfers, cold-water fishermen, and other people who are regularly exposed to frigid water should use the right kind of ear plugs.

Resources

BOOKS

Alberti, R. W. "Occupational Hearing Loss." Disorders of the Nose, Throat, Ear, Head, and Neck, edited by John Jacob Ballenger. Philadelphia: Lea & Febiger, 1991.

Bennett, J. Claude, and Fred Plum, eds. Cecil Textbook of Medicine. Philadelphia: W. B. Saunders, 1996.

"Hearing and Ear Disorders." In Alternative Medicine: The Definitive Guide, compiled by The Burton Goldberg Group. Tiburon, Calif.: Future Medicine Publishing, 1999.

Tierney, Lawrence M., M.D., et al., eds. Current Medical Diagnosis and Treatment. Stamford, CT: Appleton & Lange, 1998.

PERIODICALS

Nadol, J. B. "Hearing Loss." New England Journal of Medicine 329 (1993): 1092–102.

"Scientist Identify Gene Linked to Low-Frequency Hearing Loss." Genomics and Genetics Weekly (December 14, 2001): 6.

Sodipo, Joseph O., and Phillip A. Okeowo. "Therapeutic Acupuncture for Sensory-Neural Deafness." Am J Chin Med 8, no. 4 (1980): 385–390.

ORGANIZATIONS

Alexander Graham Bell Association for the Deaf. 3417 Volta Place NW, Washington, DC 20007-2778. (202) 337-5220. http:/www.agbell.org.

National Association of the Deaf. 814 Thayer Ave., Silver Spring, MD 20910-4500. (301) 587-1788. http://www.nad.org.

National Institute on Deafness and Other Communication Disorders, National Institutes of Health. 31 Center Dr., Bethesda, MD 20892. (301) 496-7243. Fax: (301) 402-0018. http://www.nih.gov/nidcd.

Self Help for Hard of Hearing People, Inc. 7910 Woodmont Avenue, Suite 1200, Bethesda, MD 20814. (301) 657-2248. http://www.shhh.org.

OTHER

DeafSource: An Internet Guide to Resources for Helping Professionals Working with Deaf and Hard of Hearing Individuals. http://home.earthlink.net/~drblood.

Mai Tran

Teresa G. Odle

Hearing Loss

Definition

Hearing loss is any degree of impairment of the ability to apprehend sound.

Description

Sound can be measured accurately. The term decibel (dB) refers to an amount of energy moving sound from its source to our ears or to a microphone. A drop of more than 10 dB in the level of sound a person can hear is significant.

Sound travels through a medium like air or water as waves of compression and rarefaction. These waves are collected by the external ear and cause the tympanic membrane (ear drum) to vibrate. The chain of ossicles connected to the ear drum—the incus, malleus, and stapes—carries the vibration to the oval window, increasing its amplitude 20 times on the way. There the energy causes a standing wave in the watery liquid (endolymph) inside the Organ of Corti. (A standing wave is one that does not move. A vibrating cup of coffee will demonstrate standing waves.) The configuration of the standing wave is determined by the frequency of the sound. Many thousands of tiny nerve fibers detect the highs and lows of the standing wave and transmit their findings to the brain, which interprets the signals as sound.

To summarize, sound energy passes through the air of the external ear, the bones of the middle ear and the liquid of the inner ear. It is then translated into nerve impulses, sent to the brain through nerves and understood there as sound. It follows that there are five steps in the hearing process:

• air conduction through the external ear to the ear drum

• bone conduction through the middle ear to the inner ear
• water conduction to the Organ of Corti
• nerve conduction into the brain
• interpretation by the brain.

Hearing can be interrupted in several ways at each of the five steps.

The external ear canal can be blocked with ear wax, foreign objects, infection, and tumors. Overgrowth of the bone, a condition that occurs when the ear canal has been flushed with cold water repeatedly for years, can also narrow the passageway, making blockage and infection more likely. This condition occurs often in Northern Californian surfers and is therefore called "surfer's ear."

The ear drum is so thin a physician can see through it into the middle ear. Sharp objects, pressure from an infection in the middle ear, even a firm cuffing or slapping of the ear, can rupture it. It is also susceptible to pressure changes during scuba diving.

Several conditions can diminish the mobility of the ossicles (small bones) in the middle ear. Otitis media (an infection in the middle ear) occurs when fluid cannot escape into the throat because of blockage of the eustachian tube. The fluid that accumulates, whether it be pus or just mucus and dampens the motion of the ossicles. A disease called otosclerosis can bind the stapes in the oval window and thereby cause deafness.

All the conditions mentioned so far, those that occur in the external and middle ear, are causes of conductive hearing loss. The second category, sensory hearing loss, refers to damage to the Organ of Corti and the acoustic nerve. Prolonged exposure to loud noise is the leading cause of sensory hearing loss. A million people have this condition, many identified during the military draft and rejected as being unfit for duty. The cause is often believed to be prolonged exposure to rock music. Occupational noise exposure is the other leading cause of noise induced hearing loss (NIHL) and is ample reason for wearing ear protection on the job. A third of people over 65 have presbycusis—sensory hearing loss due to aging. Both NIHL and presbycusis are primarily high frequency losses. In most languages, it is the high frequency sounds that define speech, so these people hear plenty of noise, they just cannot easily make out what it means. They have particular trouble selecting out speech from background noise. Brain infections like meningitis, drugs such as the aminoglycoside antibiotics (streptomycin, gentamycin, kanamycin, tobramycin), and Meniere's disease also cause permanent sensory hearing loss. Meniere's disease combines attacks of hearing loss with attacks of vertigo. The symptoms may occur together or separately. High doses of salicylates like aspirin and quinine can cause a temporary high-frequency loss. Prolonged high doses can lead to permanent deafness. There is an hereditary form of sensory deafness and a congenital form most often caused by rubella (German measles ).

Sudden hearing loss—at least 30dB in less than three days—is most commonly caused by cochleitis, a mysterious viral infection.

The final category of hearing loss is neural. Damage to the acoustic nerve and the parts of the brain that perform hearing are the most likely to produce permanent hearing loss. Strokes, multiple sclerosis, and acoustic neuromas are all possible causes of neural hearing loss.

Hearing can also be diminished by extra sounds generated by the ear, most of them from the same kinds of disorders that cause diminished hearing. These sounds are referred to as tinnitus and can be ringing, blowing, clicking, or anything else that no one but the patient hears.

Diagnosis

An examination of the ears and nose combined with simple hearing tests done in the physician's office can detect many common causes of hearing loss. An audiogram often concludes the evaluation, since these simple means often produce a diagnosis. If the defect is in the brain or the acoustic nerve, further neurological testing and imaging will be required.

The audiogram has many uses in diagnosing hearing deficits. The pattern of hearing loss across the audible frequencies gives clues to the cause. Several alterations in the testing procedure can give additional information. For example, speech is perceived differently than pure tones. Adequate perception of sound combined with inability to recognize words points to a brain problem rather than a sensory or conductive deficit. Loudness perception is distorted by disease in certain areas but not in others. Acoustic neuromas often distort the perception of loudness.

Treatment

Conductive hearing loss can almost always be restored to some degree, if not completely.

• matter in the ear canal can be easily removed with a dramatic improvement in hearing.
• surfer's ear gradually regresses if cold water is avoided or a special ear plug is used. In advanced cases, surgeons can grind away the excess bone.
• middle ear infection with fluid is also simple to treat. If medications do not work, surgical drainage of the ear is accomplished through the ear drum, which heals completely after treatment.
• traumatically damaged ear drums can be repaired with a tiny skin graft.
• surgical repair of otosclerosis through an operating microscope is one of the most intricate of procedures, substituting tiny artificial parts for the original ossicles.

Sensory and neural hearing loss, on the other hand, cannot readily be cured. Fortunately it is not often complete, so that hearing aids can fill the deficit.

In-the-ear hearing aids can boost the volume of sound by up to 70 dB. (Normal speech is about 60 dB.) Federal law now requires that they be dispensed only upon a physician's prescription. For complete conduction hearing loss there are now available bone conduction hearing aids and even devices that can be surgically implanted in the cochlea.

Tinnitus can sometimes be relieved by adding white noise (like the sound of wind or waves crashing on the shore) to the environment.

Decreased hearing is such a common problem that there are legions of organizations to provide assistance. Special language training, both in lip reading and signing, special schools and special camps for children are all available in most regions of the United States.

Alternative treatment

Conductive hearing loss can be treated with alternative therapies that are specific to the particular condition. Sensory hearing loss may be helped by homeopathic therapies. Oral supplementation with essential fatty acids such as flax oil and omega 3 oil can help alleviate the accumulation of wax in the ear.

KEY TERMS

Decibel— A unit of the intensity of sound, a measure of loudness.

Meniere's disease— The combination of vertigo and decreased hearing caused by abnormalities in the inner ear.

Multiple sclerosis— A progressive disease of brain and nerve tissue.

Otosclerosis— A disease that scars and limits the motion of the small conducting bones in the middle ear.

Stroke— Sudden loss of blood supply to part of the brain.

Prevention

Prompt treatment and attentive follow-up of middle ear infections in children will prevent this cause of conductive hearing loss. Control of infectious childhood diseases such as measles has greatly reduced sensory hearing loss as a complication of epidemic diseases. Laws that require protection from loud noise in the workplace have achieved substantial reduction in noise induced hearing loss. Surfers should use the right kind of ear plugs.

Resources

ORGANIZATIONS

Alexander Graham Bell Association for the Deaf. 3417 Volta Place NW, Washington, DC 20007. (202) 337-5220. 〈http://www.agbell.org〉.

Auditory-Verbal International. 2121 Eisenhower Ave., Suite 402, Alexandria, VA 22314. (703) 739-1049. 〈[email protected]〉 〈http://www.auditory-verbal.org/contact.htm〉.

Better Hearing Institute. 515 King Street, Suite 420, Alexandria, VA 22314. (703) 684-3391.

Central Institute for the Deaf. Washington University. St. Louis, Missouri. 〈http://cidmac.wustl.edu〉.

League for the Hard of Hearing. 71 West 23rd St., New York, New York 10010-4162. (212) 741-7650. 〈http://www.lhh.org〉.

National Association of the Deaf. 814 Thayer Ave., Silver Spring, MD, 20910. (301) 587-1788. 〈http://nad.policy.net〉.

Self Help for Hard of Hearing People, Inc. 7800 Wisconsin Ave., Bethesda, MD 20814. (301) 657-2248. 〈http://www.shhh.org〉.

The Sight & Hearing Association (SHA). 〈http://www.sightandhearing.org〉.

World Recreation Association of the Deaf (WRAD). 〈http://www.wrad.org〉.

Hearing Loss

Definition

Hearing loss is any degree of impairment of the ability to comprehend sound.

Description

Sound can be accurately measured. The term decibel (dB) refers to an amount of energy moving sound from its source to the ears of one or more listeners or to a microphone. A decrease of more than 10 dB in the level of sound a person can hear is significant.

Sound travels through a medium, such as air or water, as waves of compression and rarefaction. These waves are collected by the external ear and cause the tympanic membrane (ear drum) to vibrate. The chain of ossicles connected to the ear drum—the incus, malleus, and stapes—carries the vibrations to the oval window, increasing their amplitude 20 times along the way. There, the energy creates a standing wave in the watery liquid (endolymph) inside the organ of Corti. (A standing wave is one that does not move. A vibrating cup of coffee will demonstrate standing waves.) The shape of the standing wave is determined by the frequency of the sound. Many thousands of tiny nerve fibers detect the highs and lows of the standing wave. Motions in the nerve endings are converted into electrical impulses. These are transmitted to the brain via a nerve. Specialized areas of the brain interpret the signals as sound.

To summarize, sound energy passes through the air of the external ear, the bones of the middle ear, and the liquid of the inner ear. It is then translated into nerve impulses, sent to the brain through the acoustic nerve, and understood there as sound. It follows that there are five steps in the hearing process:

• air conduction through the external ear to the ear drum
• bone conduction through the middle ear to the inner ear
• water conduction inside the organ of Corti

• nerve conduction into the brain
• interpretation by the brain

Causes and symptoms

Hearing can be interrupted in several ways at each of the five steps noted above.

The external ear canal can be blocked with ear wax (cerumen), foreign objects, infection, and tumors. Overgrowth of the bone, a condition that occurs when the ear canal has been flushed with cold water repeatedly for years, can also narrow the passageway, making blockage and infection more likely. This condition occurs often among northern Californian surfers and is aptly called "surfer's ear."

The ear drum is so thin that a physician can see through it, into the middle ear. Sharp objects, pressure from an infection in the middle ear, or even a firm cuffing or slapping of the ear, can rupture the ear drum. The eardrum is also susceptible to pressure changes, such as those that occur when one is scuba diving.

Several conditions can diminish the mobility of the ossicles (small bones) in the middle ear. Otitis media (an infection in the middle ear) occurs when fluid cannot escape into the throat because of blockage of the eustachian tube. The fluid that accumulates, whether it is pus or mucus, dampens the motions of the ossicles. A disease called otosclerosis can bind the stapes in the oval window and cause deafness.

All of the problems and conditions that occur in the external and middle ear are causes of conductive hearing loss. The second category, sensory hearing loss, refers to damage to the organ of Corti, or the acoustic nerve. Prolonged exposure to loud noise is the leading cause of sensory hearing loss. More than a million people have been identified as having this condition. The cause is often believed to be prolonged exposure to loud music. Occupational noise exposure is the other leading cause of noise induced hearing loss (NIHL) and is an ample reason for wearing ear protection on the job. Jobs in construction and loud offices may contribute to ear damage, as may noises of recreation, such as loud music or the engine of a motorcycle. Both types of noises may lead to loss of hairs in one's inner ear. Thousands of these tiny hairs are attached to nerve cells in the cochlea (a snailshaped structure in the inner ear). These tiny hairs aid the conversion of sound vibrations into electrical signals, which are then transmitted to the brain. When hairs become broken or bent, the transmission of the electric signals is not as good, and sound may become muffled. Words may become difficult to distinguish against background noises.

One-third of people over 65 have presbycusis (gradual loss of hearing that occurs as one ages) and one-half of those older than age 75 have a hearing impairment. Both NIHL and presbycusis are primarily high frequency losses. The human speech frequencies are in relatively low ranges. People with presbycusis hear noise but cannot easily make sense of it. They have particular trouble distinguishing speech from background noise. Brain infections, such as meningitis, drugs such as the aminoglycoside antibiotics (e.g., streptomycin, kanamycin, tobramycin), and Meénière's disease may also cause permanent sensory hearing loss. Meénière's disease combines attacks of hearing loss with attacks of vertigo. The symptoms may occur together or separately. High doses of salicylates, like aspirin and quinine, can cause a temporary high-frequency loss. Prolonged high doses can lead to permanent deafness. There is an hereditary form of sensory deafness and a congenital form most often caused by rubella (German measles).

Sudden hearing loss—at least 30dB in less than three days—is most commonly caused by cochleitis, an inflammation of the cochlea. The source of this process is thought to be viral, but as of 2001, no causative virus has been identified.

The final category of hearing loss is neural. Damage to the acoustic nerve and the parts of the brain that integrate and interpret sounds are the most likely to produce permanent hearing loss. Strokes, multiple sclerosis, and acoustic neuromas are all possible causes of neural hearing loss.

Hearing can also be diminished by extra sounds generated by the ear, most of them from the same kinds of disorders that cause hearing loss. These sounds are referred to as tinnitus and can be ringing, blowing, clicking, or anything else that no one but the affected person hears.

Diagnosis

An examination of the ears and nose, combined with simple hearing tests that can be conducted in a physician's office, detect many common causes of hearing loss. Analysis of an audiogram often concludes the evaluation, since these simple imaging often enables a diagnosis. If the defect is in the brain or the acoustic nerve, further neurologic testing and imaging will be required.

An audiogram has many uses in diagnosing hearing deficits. The pattern of hearing loss across the audible frequencies gives clues to the cause. Several alterations in the testing procedure can give additional information. For example, speech is perceived differently than pure tones. Adequate perception of sound, combined with inability to recognize words, indicates a brain problem rather than a sensory or conductive deficit. Loudness perception is distorted by disease in certain areas of the brain, but not in others. Acoustic neuromas often distort the perception of loudness.

Treatment

Conductive hearing loss can almost always be restored to some degree, if not completely.

• Matter in the ear canal can be easily removed. This results in a dramatic improvement in hearing. In cases of earwax blockage, wax may be removed by the physician, who may loosen it and drain the ear, scoop it out, or use a suction device to removed softened wax.
• Surfer's ear gradually regresses if cold water is avoided or a special ear plug is used. In advanced cases, excess bone can be ground away by surgeons.
• Middle ear infection with fluid is also relatively easy to treat. If medications do not work, surgical drainage of the ear is accomplished through the ear drum, which heals completely after treatment.

• Traumatically damaged ear drums can be repaired with a tiny skin graft.
• Surgical repair of otosclerosis through an operating microscope is one of the most intricate procedures available, and substitutes tiny, artificial parts for the original ossicles.

Sensory and neural hearing loss, on the other hand, cannot readily be cured. Fortunately, the loss is not often complete, so that hearing aids can fill the deficit.

In-the-ear hearing aids can boost the volume of sound by up to 70 dB. (Normal speech is about 60 dB.) Federal law now requires that they be dispensed only with a physician's prescription. For complete conduction hearing loss, there are now bone conduction hearing aids available, as well as devices that can be surgically implanted in the cochlea.

Tinnitus can sometimes be relieved by adding white noise (like the sound of wind or waves crashing on the shore) to the environment.

Decreased hearing is such a common problem that there are many organizations that provide assistance. Special language training, both in lip reading and signing, and special schools and camps for hearing-impaired children are all available in most regions of the United States.

Conductive hearing loss can be treated with alternative therapies that are specific to the particular condition. Sensory hearing loss may be helped by homeopathic therapies. Oral supplementation with essential fatty acids such as flax oil and omega-3 oil can help alleviate the accumulation of wax in the ear.

Prognosis

The prognosis for conductive hearing loss is quite good. Since there is no cure for sensory or neural hearing loss, the prognosis is poor.

Health care team roles

Hearing examinations are usually conducted by physicians. Audiologists are trained to evaluate hearing. Speech language specialists are trained to provide treatment and rehabilitation for persons with impaired hearing.

Prevention

Prompt treatment and attentive follow-up of middle ear infections in children will prevent this cause of conductive hearing loss. Control of infectious childhood diseases, such as measles, has greatly reduced sensory hearing loss as a complication of epidemic diseases. Laws that require protection from loud noise in the workplace have achieved substantial reduction in noise induced hearing loss. Wearing specially designed earmuffs that resemble earphones may be of use where the noise is still too loud. Surfers should use the right kind of ear plugs.

One should have his or her hearing tested on a regular basis if a noisy environment cannot be avoided. Early detection will enable one to take steps to prevent further hearing loss. Avoiding exposure to loud noise and using hearing protection are the best ways to prevent hearing loss and slow the onset of presbycusis.

KEY TERMS

Compression— Narrower than average distances between wave peaks.

Decibel— A unit of the intensity of sound, a measure of loudness.

Meniere's disease— The combination of vertigo and decreased hearing caused by abnormalities in the inner ear.

Multiple sclerosis— A progressive disease of brain and nerve tissue.

Otosclerosis— A disease that scars and limits the motion of the small conducting bones in the middle ear.

Rarefaction— Wider than average distances between wave peaks.

Stroke— A sudden loss of blood supply to part of the brain.

Resources

BOOKS

Axelsson, Alf, Hans M. Borchgrevnik, and Roger P. Hamernick. Scientific Basis of Noise-Induced Hearing Loss. New York: Thieme Medical Pub, 1996.

Myers, David G. A Quiet World: Living With Hearing Loss. New Haven, CT: Yale University Press, 2000.

Pappas, Dennis G. Diagnosis and Treatment of Hearing Impairment in Children. Albany, NY: Delmar Publishers, 1998.

Roland, Peter S., Bradley F. Marple, and William I. Myerhoff. Hearing Loss. New York: Thieme Medical Pub, 1997.

Turkington, Carol, and Allen E. Sussman. The Encyclopedia of Deafness and Hearing Disorders, 2nd ed. New York: Facts on File, Inc., 2000.

PERIODICALS

Hager, L. "The many faces of hearing loss prevention. Occupational Health and Safety 70 (2001): 80-82, 93.

"High-tech help for hearing loss." Johns Hopkins Medical Letter on Health After 50 13 (2001): 3.

Todd, N.W. and T.M. Jarmuz. "The newborn with hearing loss." Journal of the Medical Association of Georgia 90 (2001): 32-36.

ORGANIZATIONS

American Academy of Audiology. 8300 Greensboro Dr., Suite 750, McLean, VA 22102. (800) 222-2336 or (703) 790-8466, Fax: (703) 790-8631. 〈http://www.audiology.org,〉 [email protected].

American Academy of Otolaryngology, Head and Neck Surgery. One Prince Street, Alexandria, VA 22314-3357. (703) 836-4444. 〈http://www.entnet.org/〉. [email protected].

American Speech-Language Hearing Association. 10801 Rockville Pike, Rockville, MD 20852. (800) 638-8255. 〈http://www.asha.org〉. [email protected].

Center on Deafness. 1490 Lafayette, Suite 408, Denver, CO 80203. (303) 839-8022. Fax: (303) 839-8027. 〈http://www.centerondeafness.org/services.html〉. [email protected].

National Institute on Deafness and Other Communication Disorders. National Institutes of Health, 31 Center Drive, MSC 2320, Bethesda, MD 20892-2320. 〈http://www.nidcd.nih.gov〉.

Rochester Institute of Technology. 90 Lomb Memorial Dr. Rochester, NY 14623. (716) 475-2562. 〈http://wally.rit.edu/internet/subject/deafness.html〉. [email protected].

OTHER

American Academy of Audiology Web Search. 〈http://www.searchwave.com/search〉.

Baylor College of Medicine. 〈http://www.bcm.tmc.edu/oto/studs/innear.html〉.

MayoClinic Web Search. 〈http://www.mayoclinic.com/home?id=5.1.1.8.21〉.

National Academy of Science. 〈http://www4.nas.edu/beyond/beyonddiscovery.nsf/web/cochlear11?OpenDocument〉.

National Council on Aging: 〈http://www.ncoa.org/news/archives/hearing_loss.htm〉.

National Institute for Occupational Safety and Health. 〈http://www.cdc.gov/niosh/noise.html〉.

Hearing disorders

Definition

Hearing disorders range from a temporary, partial loss of hearing to the permanent loss of hearing known as deafness.

Description

The variety of hearing disorders includes a loss or decrease in the ability to discern certain frequencies of sound, a ringing or other noise that is unrelated to any actual external sound, damage due to physical trauma or infection, and genetically determined structural malformation.

Demographics

Hearing disorders occur worldwide in all races. The hearing loss that occurs with age is very common, affecting an estimated 30% of Americans over 60 years of age and 50% of those older than 75.

Tinnitus, a ringing or noisy sensation in the ears, is quite common with an estimated 20% of people affected worldwide. In the United States alone, some 36 million people experience tinnitus.

For hearing loss caused by otosclerosis, middle-aged Caucasian women are more prone than others, perhaps as a consequence of hormonal changes. In otosclerosis, abnormal bone development occurs in the middle ear, resulting in progressive hearing loss. Sudden hearing loss happens more often to people ages 30–60 for unknown reasons.

Causes and symptoms

Presbycusis

Presbycusis (or sensorineural hearing loss) is the loss of hearing that occurs with age. The condition results from the long-term assault on the ear structures, particularly on the inner ear, from a lifetime of noise, ear infections, or growths on bones of the outer or middle ear. The inner ear is where the vibrational sound waves are converted to electrical signals, courtesy of thousands of tiny hairs that are in a fluid-enclosed space called the cochlea. The hairs are connected to nerve cells, which send the electrical signals to the brain.

Most age-related hearing loss is due to damage to the cochlea. The tiny hairs can bend or even break, and the attached nerve cells can degenerate. The resulting less-efficient transmission of the electrical signal, particularly of higher-pitched tones, causes hearing loss.

Symptoms of presbycusis typically include increased difficulty in making out sounds of a certain volume or tone, especially when background sounds are present.

Conductive hearing loss

In conductive hearing loss, sound is not transmitted efficiently through the outer and middle ears. These regions house the eardrum, ear canal, and the trio of tiny bones (ossicles) in the middle ear that transmits sound energy to the inner ear. The hearing loss can be due to malformation of structures like the canal or the ossicles, dense buildup of ear wax, or fluid in the ear due to colds, allergies, or infections like otitis media. Symptoms include a decreased ability to detect fainter sounds and a general lowering of the sound level that can be detected.

Otitis media

Otitis media is an inflammation in the middle ear that is usually accompanied by fluid buildup. The condition may be transient in some children, but persistent in others to the point of requiring surgical correction. In developed countries, otitis media is second to the common cold as the most common health problem in preschool-aged children. Hearing loss occurs because of the fluid accumulation and the resulting suppression of sound waves moving to the inner ear.

Central auditory processing disorders

Central auditory processing disorders result in hearing loss when the areas of the brain involved in hearing are damaged. Sources of damage include disease, injury, and tumor growth. Consistent with the variety of causes, the symptoms of the disorders include the inability to hear certain sounds, inability to tell one sound from another, and the inability to recognize a pattern such as speech in sounds.

Congenital hearing loss

Congenital hearing loss is present from birth and is caused by a genetic defect or disturbance during fetal development. Genetic factors cause more than half of all such disorders. Depending on the nature of the genetic defect, the occurrence of the hearing loss may be common or rare. For example, if both parents have a genetically determined hearing deficiency, the chance of passing the trait to their children is high. In other cases, people who have normal hearing carry a second, defective copy of a crucial gene. The chance of passing on the hearing loss is 25%.

Hearing loss at birth can also be caused by pre-birth infections such as measles, cytomegalovirus, or herpes simplex virus.

Otosclerosis

The abnormal growth of the bone of the middle ear prevents the ossicles, particularly the last of the trio of bones (the stapes), from properly transmitting sound waves to the inner ear in otosclerosis. The cause(s) of otosclerosis are not clear, although observations that the disorder spans family generations make a genetic source likely.

The diminished hearing that occurs is not sudden. Rather, the change is gradual and is usually recognized when the person becomes aware that she or he can no longer hear a low-pitched sound such as a whisper.

Other genetically based hearing losses

Usher syndrome affects both the ears and eyes. The defective genes that are at the heart of the malady are passed from parents to children. Depending on the nature of the syndrome, children can be born with moderate to severe hearing loss, or can be totally deaf. Others begin life essentially normal, with hearing loss progressively worsening to deafness by the teenage years.

Waardenburg syndrome affects both the ears and the color of the skin, eyes, or hair. Eyes can be different colors and hair can have a patch of white or become prematurely gray. Hearing can range from normal to severely impaired. At least four genes can produce the syndrome when they undergo mutation.

Ménière's disease

Ménière's disease is a change in the volume of the inner ear that produces swelling, pressure, pain , intermittent hearing loss, dizziness , and tinnitus. Swelling may be so pronounced that membranes like the eardrum can rupture. As well, some people report that their voice sounds louder than normal. The disease may be caused by a viral or bacterial infection.

Tinnitus

Tinnitus is a ringing noise or other sound that occurs in the absence of an external source of sound. For some, tinnitus is an infrequent occurrence. Others are very inconvenienced by near-constant tinnitus. The noises experienced in tinnitus range in description and include electronic noise, hissing steam, chirping crickets, bells, breaking glass, buzzing, and even the noise of a chainsaw. The noises can be constant or may rise and fall in volume with head motion or with the planting of feet during running.

Tinnitus has various known triggers. Foods such as red wine, cheese, and chocolate have been implicated. Over-the-counter drugs such as ibuprofen and extra-strength aspirin, and prescribed drugs, including oral contraceptives and aminoglycoside antibiotics, can cause tinnitus. Drug-related tinnitus disappears when the dosage is reduced or the drug stopped. The growth of certain tumors can cause tinnitus.

The aging of the inner ear is also a factor in tinnitus. As nerve cells deteriorate and the many hairs in the cochlea that transmit sound waves to the nerves become damaged and broken with time, the signaling of sound impulses to the brain becomes faulty. Nerves may fire when there has been no stimulus. The brain interprets the signal as actual noise.

Sudden deafness or sudden sensorineural hearing loss

This rapid decrease or complete loss of hearing can occur within minutes or over the course of several days. The hearing loss typically affects one ear and often resolves with time. Sudden deafness is much more serious and should be treated as a medical emergency requiring immediate medical attention. Causes are unclear and may involve an infection, head injury, reaction to a drug, problems with circulation, and other disorders such as multiple sclerosis .

Deafness

The complete loss of hearing can be due to genetically determined developmental difficulties, a trauma such as a loud noise, physical damage to structures in the ear, nerves, or relevant areas of the brain, and infection during pregnancy (such as rubella). In a great many cases, deafness is permanent. Childhood deafness typically becomes apparent when a child appears inattentive and fails to meet language milestones.

Diagnosis

Presbycusis is usually first detected by a family physician. Diagnosis is subsequently made by a hearing specialist or an audiologist, and involves a hearing test in which sounds of differing frequencies and gradually decreasing volume are sent to one ear at a time.

Tinnitus is self-evident, as the ringing or other sensation is impossible to ignore. In contrast, otitis media can be difficult to diagnose, as it is often not accompanied by pain or a fever. Fluid in the ear can be a sign of otitis media. Also, changes in children's behavior such as playing the television louder, misunderstanding directions, and pulling at the ears can all be indicators of otitis media.

Imaging of the inside of the ear using the technique of magnetic resonance imaging (MRI) can be useful in diagnosing Ménière's disease. Usher syndrome is diagnosed by the simultaneous appearance of ear and eye problems.

Treatment team

The varied treatment can involve the family physician and more specialized doctors, including audiologists and otolaryngologists (specialists in ear, nose, and throat disorders). As well, speech-language pathologists can be involved in the treatment of hearing loss-related speech disorders in children.

Treatment

Treatment for presbycusis can be as simple as keeping the ear canals free from sound-muffling wax buildup. Another fairly common treatment for older people is the use of a hearing aid, which amplifies sound and directs the sound into the ear canal. About 20% of those with age-related hearing loss can benefit from an aid. More severe presbycusis can be treated using a cochlear implant. The device actually compensates for the nonworking parts of the inner ear. Conductive hearing loss can usually be fully corrected by medication or surgery. Similarly, when tinnitus is caused by overmedication, the condition is alleviated by modifying or eliminating the dosage of the drug.

Ménière's disease and Usher syndrome cannot be cured, however, the symptoms can be greatly relieved by release of the buildup of pressure in the inner ear and the use of hearing aids or implants, respectively. Coping strategies and increased knowledge of the conditions can then help a person lead an essentially normal life.

Otosclerosis that is more pronounced can be treated by a surgical procedure called a stapedectomy, in which the damaged portion of the middle ear, the stapes, one of the three bones of the middle ear, is bypassed by an implanted device that routes sound to the inner ear. Milder otosclerosis may be lessened by the use of a hearing aid.

Recovery and rehabilitation

Some conditions that can be addressed by surgery or the use of a hearing aid or an implant have varying levels of recovery. Other conditions involving permanent deafness cannot be cured.

Clinical trials

As of April 2004, at least eight clinical trials were active in the United States. Most focus on deafness, in particular the determination of the genetic factors that contribute to or cause deafness. Updated information on these studies can be found at the National Institutes of Health Web site for clinical trials at <http://www.clinicaltrials.gov>.

Prognosis

Age-related hearing loss can be partially or almost completely compensated for by a change in lifestyle and the development of coping skills (listening to the radio at higher volume, different conversational behavior in crowds, use of hearing aids or implants). Otitis media can cause delayed speech development, if undiagnosed, because of the child's impaired ability to hear. Sudden hearing loss usually resolves on its own within a few days to several weeks. However, in about 15% of cases, the condition worsens with time.

Special concerns

The various surgeries that can be performed all carry some risk, and the quality of sound that is provided by cochlear implants varies greatly among recipients.

Additionally, tinnitus can be caused by the buildup of cholesterol in arteries around the ear, high blood pressure, and by malformed arteries or veins. Tinnitus, therefore, may be an indication of a more serious health problem.

Resources

BOOKS

Dugan, Marcia B. Living with Hearing Loss. Baltimore: Gallaudet Press, 2003.

Schwartz, Sue. Choices in Deafness: A Parents'Guide to Communication Options. Bethesda, MD: Woodbine House, 2003.

PERIODICALS

DeJonckere, P. H., and G. G. de Surgeres. "Acute Tinnitus and Permanent Audiovestibular Damage after Hepatitis B Vaccination." International Tinnitus Journal (July 2001): 59–61.

Waddell, A., and R. Canter. "Tinnitus." American Family Physician (February 2004): 591–592.

OTHER

"Hearing Loss." MayoClinic.com. April 8, 2004 (May 30, 2004). <http://www.mayoclinic.com/invoke.cfm?id=DS00172>.

"Tinnitus." MayoClinic.com. April 8, 2004 (May 30, 2004). <http://www.mayoclinic.com/invoke.cfm?id=DS00365>.

ORGANIZATIONS

American Academy of Audiology. 8300 Greensboro Drive, Suite 750, McLean, VA 22102. (703) 790-8466 or (800) 222-2336; Fax: (703) 790-8631. [email protected]. <http://www.audiology.org>.

American Speech-Language-Hearing Association. 10801 Rockville Pike, Rockville, MD 20852. (301) 638-8255 or (800) 638-8255; Fax: (301) 571-0457. [email protected]. <http://www.asha.org>.

American Tinnitus Association. PO Box 5, Portland, OR 97207-0005. (503) 248-9985 or (800) 634-8978; Fax: (503) 248-0024. [email protected]. <http://www.ata.org>.

Deafness Research Foundation. 1050 17th Street NW, Suite 701, Washington, DC 20036. (202) 289-5850. <http://www.drf.org>.

National Center on Deafness. 18111 Nordhoff Street, Northridge, CA 91330-8267. (818) 677-2145; Fax: (818) 677-7693. [email protected]. <http://ncod.csun.edu>.

National Institute on Deafness and Other Communication Disorders, National Institutes of Health. 31 Center Drive, MSC 2320, Bethesda, MD 20892-2320. (301) 496-7243 or (800) 241-1044; Fax: (301) 402-0018. [email protected]. <http://www.nidcd.nih.gov>.

Brian Douglas Hoyle, PhD

Hearing loss

Definition

Hearing loss is any degree of impairment of the ability to comprehend sound.

Description

Sound can be accurately measured. The term decibel (dB) refers to an amount of energy moving sound from its source to the ears of one or more listeners or to a microphone. A decrease of more than 10 dB in the level of sound a person can hear is significant.

Sound travels through a medium, such as air or water, as waves of compression and rarefaction. These waves are collected by the external ear and cause the tympanic membrane (ear drum) to vibrate. The chain of ossicles connected to the ear drum—the incus, malleus, and stapes—carries the vibrations to the oval window, increasing their amplitude 20 times along the way. There, the energy creates a standing wave in the watery liquid (endolymph) inside the organ of Corti. (A standing wave is one that does not move. A vibrating cup of coffee will demonstrate standing waves.) The shape of the standing wave is determined by the frequency of the sound. Many thousands of tiny nerve fibers detect the highs and lows of the standing wave. Motions in the nerve endings are converted into electrical impulses. These are transmitted to the brain via a nerve. Specialized areas of the brain interpret the signals as sound.

To summarize, sound energy passes through the air of the external ear, the bones of the middle ear, and the liquid of the inner ear. It is then translated into nerve impulses, sent to the brain through the acoustic nerve, and understood there as sound. It follows that there are five steps in the hearing process:

• air conduction through the external ear to the ear drum
• bone conduction through the middle ear to the inner ear
• water conduction inside the organ of Corti
• nerve conduction into the brain
• interpretation by the brain

Causes and symptoms

Hearing can be interrupted in several ways at each of the five steps noted above.

The external ear canal can be blocked with ear wax (cerumen), foreign objects, infection , and tumors. Overgrowth of the bone, a condition that occurs when the ear canal has been flushed with cold water repeatedly for years, can also narrow the passageway, making blockage and infection more likely. This condition occurs often among northern Californian surfers and is aptly called "surfer's ear."

The ear drum is so thin that a physician can see through it, into the middle ear. Sharp objects, pressure from an infection in the middle ear, or even a firm cuffing or slapping of the ear, can rupture the ear drum. The eardrum is also susceptible to pressure changes, such as those that occur when one is scuba diving.

Several conditions can diminish the mobility of the ossicles (small bones) in the middle ear. Otitis media (an infection in the middle ear) occurs when fluid cannot escape into the throat because of blockage of the eustachian tube. The fluid that accumulates, whether it is pus or mucus, dampens the motions of the ossicles. A disease called otosclerosis can bind the stapes in the oval window, thereby cause deafness.

All of the problems and conditions that occur in the external and middle ear are causes of conductive hearing loss. The second category, sensory hearing loss, refers to damage to the organ of Corti, or the acoustic nerve. Prolonged exposure to loud noise is the leading cause of sensory hearing loss. More than a million people have been identified as having this condition. The cause is often believed to be prolonged exposure to loud music. Occupational noise exposure is the other leading cause of noise induced hearing loss (NIHL) and is an ample reason for wearing ear protection on the job. Jobs in construction and loud offices may contribute to ear damage, as may noises of recreation, such as loud music or the engine of a motorcycle. Both types of noises may lead to loss of hairs in one's inner ear. Thousands of these tiny hairs are attached to nerve cells in the cochlea (a snail-shaped structure in the inner ear). These tiny hairs aid the conversion of sound vibrations into electrical signals, which are then transmitted to the brain. When hairs become broken or bent, the transmission of the electric signals isn't as good, and sound may become muffled. Words may become difficult to distinguish against background noises.

One-third of people over 65 have presbycusis (gradual loss of hearing that occurs as one ages) and one-half of those older than age 75 have a hearing impairment. Both NIHL and presbycusis are primarily high frequency losses. The human speech frequencies are in relatively low ranges. People with presbycusis hear noise but cannot easily make sense of it. They have particular trouble distinguishing speech from background noise. Brain infections, such as meningitis , drugs such as the amino-glycoside antibiotics (e.g., streptomycin, kanamycin, tobramycin), and Menière's disease may also cause permanent sensory hearing loss. Menière's disease combines attacks of hearing loss with attacks of vertigo. The symptoms may occur together or separately. High doses of salicylates, like aspirin and quinine, can cause a temporary high-frequency loss. Prolonged high doses can lead to permanent deafness. There is an hereditary form of sensory deafness and a congenital form most often caused by rubella (German measles).

Sudden hearing loss—at least 30dB in less than three days—is most commonly caused by cochleitis, an inflammation of the cochlea. The source of this process is thought to be viral, but as of 2001, no causative virus has been identified.

The final category of hearing loss is neural. Damage to the acoustic nerve and the parts of the brain that integrate and interpret sounds are the most likely to produce permanent hearing loss. Strokes, multiple sclerosis , and acoustic neuromas are all possible causes of neural hearing loss.

Hearing can also be diminished by extra sounds generated by the ear, most of them from the same kinds of disorders that cause hearing loss. These sounds are referred to as tinnitus and can be ringing, blowing, clicking, or anything else that no one but the affected person hears.

Diagnosis

An examination of the ears and nose, combined with simple hearing tests that can be conducted in a physician's office, detect many common causes of hearing loss. Analysis of an audiogram often concludes the evaluation, since these simple imaging often enables a diagnosis. If the defect is in the brain or the acoustic nerve, further neurologic testing and imaging will be required.

An audiogram has many uses in diagnosing hearing deficits. The pattern of hearing loss across the audible frequencies gives clues to the cause. Several alterations in the testing procedure can give additional information. For example, speech is perceived differently than pure tones. Adequate perception of sound, combined with inability to recognize words, indicates a brain problem rather than a sensory or conductive deficit. Loudness perception is distorted by disease in certain areas of the brain, but not in others. Acoustic neuromas often distort the perception of loudness.

Treatment

Conductive hearing loss can almost always be restored to some degree, if not completely.

• Matter in the ear canal can be easily removed. This results in a dramatic improvement in hearing. In cases of earwax blockage, wax may be removed by the physician, who may loosen it and drain the ear, scoop it out, or use a suction device to removed softened wax.

• Surfer's ear gradually regresses if cold water is avoided or a special ear plug is used. In advanced cases, excess bone can be ground away by surgeons.
• Middle ear infection with fluid is also relatively easy to treat. If medications do not work, surgical drainage of the ear is accomplished through the ear drum, which heals completely after treatment.
• Traumatically damaged ear drums can be repaired with a tiny skin graft.
• Surgical repair of otosclerosis through an operating microscope is one of the most intricate procedures available, and substitutes tiny, artificial parts for the original ossicles.

Sensory and neural hearing loss, on the other hand, cannot readily be cured. Fortunately, the loss is not often complete, so that hearing aids can fill the deficit.

In-the-ear hearing aids can boost the volume of sound by up to 70 dB. (Normal speech is about 60 dB.) Federal law now requires that they be dispensed only with a physician's prescription. For complete conduction hearing loss, there are now bone conduction hearing aids available, as well as devices that can be surgically implanted in the cochlea.

Tinnitus can sometimes be relieved by adding white noise (like the sound of wind or waves crashing on the shore) to the environment.

Decreased hearing is such a common problem that there are many organizations that provide assistance. Special language training, both in lip reading and signing, and special schools and camps for hearing-impaired children are all available in most regions of the United States.

Conductive hearing loss can be treated with alternative therapies that are specific to the particular condition. Sensory hearing loss may be helped by homeopathic therapies. Oral supplementation with essential fatty acids such as flax oil and omega-3 oil can help alleviate the accumulation of wax in the ear.

Prognosis

The prognosis for conductive hearing loss is quite good. Since there is no cure for sensory or neural hearing loss, the prognosis is poor.

Health care team roles

Hearing examinations are usually conducted by physicians. Audiologists are trained to evaluate hearing. Speech language specialists are trained to provide treatment and rehabilitation for persons with impaired hearing.

Prevention

Prompt treatment and attentive follow-up of middle ear infections in children will prevent this cause of conductive hearing loss. Control of infectious childhood diseases, such as measles, has greatly reduced sensory hearing loss as a complication of epidemic diseases. Laws that require protection from loud noise in the workplace have achieved substantial reduction in noise induced hearing loss. Wearing specially designed earmuffs that resemble earphones may be of use where the noise is still too loud. Surfers should use the right kind of ear plugs.

One should have his or her hearing tested on a regular basis if a noisy environment cannot be avoided. Early detection will enable one to take steps to prevent further hearing loss. Avoiding exposure to loud noise and using hearing protection are the best ways to prevent hearing loss and slow the onset of presbycusis.

KEY TERMS

Compression —Narrower than average distances between wave peaks.

Decibel —A unit of the intensity of sound, a measure of loudness.

Meniere's disease —The combination of vertigo and decreased hearing caused by abnormalities in the inner ear.

Multiple sclerosis —A progressive disease of brain and nerve tissue.

Otosclerosis —A disease that scars and limits the motion of the small conducting bones in the middle ear.

Rarefaction —Wider than average distances between wave peaks.

Stroke —A sudden loss of blood supply to part of the brain.

Resources

BOOKS

Axelsson, Alf, Hans M. Borchgrevnik, and Roger P. Hamernick. Scientific Basis of Noise-Induced Hearing Loss. New York: Thieme Medical Pub, 1996.

Myers, David G. A Quiet World: Living With Hearing Loss. New Haven, CT: Yale University Press, 2000.

Pappas, Dennis G. Diagnosis and Treatment of Hearing Impairment in Children. Albany, NY: Delmar Publishers, 1998.

Roland, Peter S., Bradley F. Marple, and William I. Myerhoff. Hearing Loss. New York: Thieme Medical Pub, 1997.

Turkington, Carol, and Allen E. Sussman. The Encyclopedia of Deafness and Hearing Disorders, 2nd ed. New York: Facts on File, Inc., 2000.

PERIODICALS

Anonymous. "High-tech Help for Hearing Loss." Johns Hopkins Medical Letter on Health After 50 13 (2001): 3.

Hager L. "The Many Faces of Hearing Loss Prevention. Occupational Health and Safety 70 (2001): 80-82, 93.

Todd, N. W., and T. M. Jarmuz. "The Newborn with Hearing Loss." Journal of the Medical Association of Georgia 90(2001): 32-36.

ORGANIZATIONS

American Academy of Audiology. 8300 Greensboro Dr., Suite 750, McLean, Virginia 22102. (800) 222-2336. (703) 790-8466. Fax: (703) 790-8631. <http://www.audiology.org>. [email protected].

American Academy of Otolaryngology, Head and Neck Surgery. One Prince Street, Alexandria, VA 22314-3357.(703) 836-4444. <http://www.entnet.org/.> [email protected].

American Speech-Language Hearing Association. 10801 Rockville Pike, Rockville, MD 20852. (800) 638-8255. <http://www.asha.org>. [email protected].

Center on Deafness. 1490 Lafayette, Suite 408, Denver, CO 80203. (303) 839-8022. Fax: (303) 839-8027. <http://www.centerondeafness.org/services.html>. [email protected].

National Institute on Deafness and Other Communication Disorders, National Institutes of Health. 31 Center Drive, MSC 2320, Bethesda, MD 20892-2320. <http://www.nidcd.nih.gov>.

OTHER

American Academy of Audiology Web Search. <http://www.searchwave.com/search>.

Baylor College of Medicine. <http://www.bcm.tmc.edu/oto/studs/innear.html>.

MayoClinic. <http://www.mayoclinic.com/home?id=5.1.1.8.21>.

National Academy of Science. <http://www4.nas.edu/beyond/beyonddiscovery.nsf/web/cochlear11?OpenDocument>.

National Council on Aging. <http://www.ncoa.org/news/archives/hearing_loss.htm>.

National Institute for Occupational Safety and Health. <http://www.cdc.gov/niosh/noise.html>.

Rochester Institute of Technology. 90 Lomb Memorial Dr. Rochester, NY 14623. 716-475-2562. <http://wally.rit.edu/internet/subject/deafness.html>. [email protected].

L. Fleming Fallon Jr., M.D, Ph.D, Dr.PH