Hearing loss is the reduced ability to hear sound. Deafness is the complete inability to hear sound. Deafness and hearing loss have many causes and can occur at any age. People can go deaf suddenly as a complication of a virus, or lose their hearing over time because of disease, nerve damage, or injury caused by noise. About 1 to 2 in 1,000 babies are born with significant hearing loss, often because of genetic factors. Approximately 20% of adults in Canada have at least mild hearing loss, and almost half of Canadians over 60 years of age have hearing loss.
Hearing loss is a spectrum with minor hearing problems at one end and profound, complete deafness at the other. Conductive hearing loss occurs when something blocks sound waves from reaching the inner ear. Sensorineural hearing loss is caused by damage to the inner ear or to the nerves that send sound to the brain. Sensorineural hearing loss is more likely to be permanent and to cause deafness.
Sometimes a mixture of conductive and sensorineural hearing loss can occur.
Many different conditions lead to partial and total deafness. Ear infections, fluid buildup behind the eardrum, holes in the eardrum, and problems with the middle ear bones can cause deafness from conductive hearing loss. In rare cases, tumours can also cause conductive hearing loss – they block sound from getting into the inner ear. Birth defects and diseases passed on by genes can do this, too. Genetics is one cause of sensorineural hearing loss. Half of all cases of profound deafness in children have a genetic source.
Presbycusis, or age-associated hearing loss, also has a genetic component. It's a condition that makes someone deaf over time as they age due to the slow decay of sensitive hair cells lining the inner ear. Aside from aging, other causes of the decay include circulatory problems, diseases such as diabetes, and long-term exposure to noise. Without the hair cells, recognizing sounds becomes difficult or impossible.
Exposure to loud noise in certain occupations from sources such as construction machinery, heavy equipment, or amplified music can cause sensorineural hearing loss in people of all ages and is the most common cause of hearing loss. Other sources of excess noise include attendance at concerts and nightclubs, and use of music headphones, household power tools, or firearms. The louder the noise, and the longer a person is exposed to it, the greater their risk of this type of hearing loss. To prevent this type of hearing loss it is important to wear proper hearing protection and avoid exposure to loud noise whenever possible.
Some kinds of sensorineural hearing loss or deafness may be caused by infectious diseases, such as shingles, meningitis, and cytomegalovirus. In childhood, the auditory nerve can be damaged by mumps, meningitis, German measles (rubella), or inner ear infections.
More rarely, deafness or hearing loss can occur suddenly. This condition can be permanent or temporary, and usually affects only one ear. The cause is unknown but may be due to viral infections, or disorders of the circulatory or immune system. The loss is potentially reversible with corticosteroid medications; however, the likelihood of recovery is lower if the loss was severe initially. Treatment is more likely to have greater effect if it is started early – ideally within a week of the loss of hearing.
If a woman contracts German measles during pregnancy, her child may have a permanent hearing disability. Lack of oxygen at birth can also badly damage the ears and hearing.
Other causes of sensorineural hearing loss include diabetes and various brain and nerve disorders (such as a stroke). Tumours of the auditory nerve or brain are rare causes of hearing loss. High doses of acetylsalicylic acid* (ASA), quinine, some antibiotics, and diuretics used to treat high blood pressure may all permanently damage the inner ear. Nerve pathways in the brain that transmit sound impulses can be damaged by multiple sclerosis and other diseases attacking the coverings of nerves. Violent injury and physical blows to the ear may cause permanent deafness.
Symptoms and Complications
Profound deafness is easy to recognize, since people will notice such a large change in hearing. Milder hearing loss may not be noticed right away, since it often comes on gradually and people "get used to it." If you notice that you need to turn the volume up on the radio or television, have difficulty understanding conversations, or need to ask people to repeat what they say, you may have hearing loss.
Age-related hearing loss often starts at the high frequencies, meaning that people may have trouble understanding women and children (whose voices are higher pitched) or telling the difference between similar sounds such as "th" and "sh." Many people are alerted by friends or relatives. The problem is initially most apparent in noisy environments.
All infants and children should be screened for hearing loss, as early diagnosis and intervention can have a dramatic impact on the child's future development and educational needs. Signs of deafness in young children include not responding to noises, responding slowly, or not learning to speak by the expected age. A deaf child may also lag behind in developing motor skills and coordination, or in learning how to balance, crawl, or walk. Profoundly deaf children are usually diagnosed by the age of 2. The biggest obstacles to early diagnosis are typically a delay in a referral to a specialist (usually when the signs of hearing loss are not recognized), or a lack of access to appropriate infant hearing screening.
Making the Diagnosis
Using an otoscope (a little hand-held instrument with a light), your doctor will examine your ear to make sure the ear canal is not blocked and to check for an ear infection. Your doctor may use a tuning fork to help determine if hearing loss is conductive or sensorineural.
Your doctor may refer you to another doctor who specializes in hearing disorders (otologists or otolaryngologists). There are many tests to measure hearing loss or track down its cause.
Audiometry is a test that measures hearing loss with an electronic device. To find out whether babies and children have profound hearing loss, doctors use otoacoustic emissions testing (OAEs). If an infant or child fails otoacoustic emissions testing, auditory brain stem response (ABR) testing is performed.
Neurological tests including a magnetic resonance imaging (MRI) test or a computerized tomography (CT) scan may be performed to check for possible tumours involving the auditory (hearing) nerve, especially for people with hearing loss that is significantly worse in one ear.
Treatment and Prevention
Sensorineural hearing loss or deafness tends to be permanent because it involves damage to nerves or to the inner ear. The only method of treatment is a hearing aid worn in the ear, a device that amplifies the volume of sound electronically. Hearing aids are usually some variation of an in-the-ear or behind-the-ear device. Many are programmable to make them more effective for use in a variety of situations, such as noisy environments or talking on the phone.
The body aid, although rarely used now, is the most powerful kind of hearing aid for profound deafness, and is worn in a harness on the chest. A bone-conducting hearing aid may be used if someone was born without an ear canal (the opening leading to the inner ear). The aid conducts sound through the skull to the inner ear, and can be implanted surgically in the bone behind the ear.
Conductive hearing loss and deafness may at times be treatable by removing the cause of the blockage, for example, wax in the ear canal or fluid in the middle ear. Problems with the hearing bones (called otosclerosis) can be treated with surgery.
If a person can't hear sounds even with a hearing aid, they may benefit from a cochlear implant. Very thin wires are implanted in the inner ear. They connect the auditory nerve with a device that converts sound into electrical impulses. These stimulate the auditory nerve, which then sends the impulses to the brain. Many people with modern, multi-channel cochlear implants are able to understand speech without lip reading, including speech over the telephone. Other tools to help the profoundly deaf include light alerting systems (e.g., they flash if a doorbell is ringing) and telephone communication devices.
In order to communicate, many deaf people lip-read or use sign language. Deaf infants and older children need special language training that should begin as soon as deafness is identified. This involves the teaching of sign language and lip reading, as well as speech therapy.
Hearing problems can be prevented by reducing exposure to noise. Hearing protection should be used when using machinery or when exposed to loud noises of any sort. People should not listen to excessively loud music on headphones. It is important that children get all their vaccinations to lower the risk of infectious diseases that may lead to permanent hearing loss or deafness. Avoiding certain medications can prevent drug-induced ear damage. If complete avoidance is not possible, monitoring levels of these medications in the blood allows health professionals to keep them at safe levels in the body.
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