| Hearing loss | |
|---|---|
| Other names | Deaf or hard of hearing; anakusis or anacusis is total deafness[1] |
 | |
| Specialty | Otorhinolaryngology,audiology |
| Symptoms | Decreased ability to hear |
| Complications | Social isolation,[2]dementia |
| Types | Conductive,sensorineural, and mixed hearing loss,central auditory dysfunction[3] |
| Causes | Genetics,aging,exposure to noise, someinfections, birth complications, trauma to the ear, certain medications or toxins[2] |
| Diagnostic method | Hearing tests |
| Prevention | Immunization, proper care aroundpregnancy, avoiding loud noise, avoiding certain medications[2] |
| Treatment | Hearing aids,sign language,cochlear implants,closed captioning,subtitles[2] |
| Frequency | 1.33 billion / 18.5% (2015)[4] |
Hearing loss is a partial or total inability tohear.[5] Hearing loss may be present at birth or acquired at any time afterwards.[6][7] Hearing loss may occur in one or both ears.[2] In children, hearing problems can affect the ability toacquire spokenlanguage, and in adults it can create difficulties with social interaction and at work.[8] Hearing loss can be temporary or permanent.Hearing loss related to age usually affects both ears and is due tocochlear hair cell loss.[9] In some people, particularly older people, hearing loss can result in loneliness.[2]
Hearing loss may be caused by a number of factors, including:genetics,ageing,exposure to noise, someinfections, birth complications, trauma to the ear, and certain medications or toxins.[2] A common condition that results in hearing loss ischronic ear infections.[2] Certain infections during pregnancy, such ascytomegalovirus,syphilis andrubella, may also cause hearing loss in the child.[2][10] Hearing loss is diagnosed whenhearing testing finds that a person is unable to hear 25decibels in at least one ear.[2] Testing for poor hearing is recommended for all newborns.[8] Hearing loss can be categorized as mild (25 to 40dB), moderate (41 to 55 dB), moderate-severe (56 to 70 dB), severe (71 to 90 dB), or profound (greater than 90 dB).[2] There are three main types of hearing loss:conductive hearing loss,sensorineural hearing loss, and mixed hearing loss.[3]
About half of hearing loss globally is preventable through public health measures.[2] Such practices includeimmunization, proper care aroundpregnancy, avoiding loud noise, and avoiding certain medications.[2] TheWorld Health Organization recommends that young people limit exposure to loud sounds and the use ofpersonal audio players to an hour a day in an effort to limit exposure to noise.[11] Early identification and support are particularly important in children.[2] For many,hearing aids,sign language,cochlear implants andsubtitles are useful.[2]Lip reading is another useful skill some develop.[2] Access to hearing aids, however, is limited in many areas of the world.[2]
As of 2013 hearing loss affects about 1.1 billion people to some degree.[12] It causes disability in about 466 million people (5% of the global population), and moderate to severe disability in 124 million people.[2][13][14] Of those with moderate to severe disability 108 million live in low and middle income countries.[13] Of those with hearing loss, it began during childhood for 65 million.[15] Those who use sign language and are members ofDeaf culture may see themselves as having a difference rather than adisability.[16] Many members of Deaf culture oppose attempts to cure deafness[17][18][19] and some within this community view cochlear implants with concern as they have the potential to eliminate their culture.[20]
Use of the terms "hearing impaired", "deaf-mute", or "deaf and dumb" to describe deaf and hard of hearing people is discouraged by many in the deaf community as well as advocacy organizations, as they are offensive to many deaf and hard of hearing people.[23][24]
Human hearing extends in frequency from 20 to 20,000 Hz, and in intensity from 0 dB to 120 dB HL or more. 0 dB does not represent absence of sound, but rather the softest sound an average unimpaired human ear can hear; some people can hear down to −5 or even −10 dB. Sound is generally uncomfortably loud above 90 dB and 115 dB represents thethreshold of pain. The ear does not hear all frequencies equally well: hearing sensitivity peaks around 3,000 Hz. There are many qualities of human hearing besides frequency range and intensity that cannot easily be measured quantitatively. However, for many practical purposes, normal hearing is defined by a frequency versus intensity graph, or audiogram, charting sensitivity thresholds of hearing at defined frequencies. Because of the cumulative impact of age and exposure to noise and other acoustic insults, 'typical' hearing may not be normal.[25][26]
The presentation is as follows:[citation needed]
Hearing loss is sensory, but may have accompanying symptoms:[citation needed]
There may also be accompanying secondary symptoms:[citation needed]
Hearing loss is associated withAlzheimer's disease anddementia.[27] The risk increases with the hearing loss degree. Asystematic review andmeta analysis assessed the link between hearing loss and dementia subtypes. Hearing loss was linked to an increased risk of mild to severe cognitive problems, includingmild cognitive impairment and Alzheimer’s disease. Hearing loss was not linked to an increased risk ofvascular dementia.[28][29] There are several hypotheses including cognitive resources being redistributed to hearing and social isolation from hearing loss having a negative effect.[30] According to preliminary data,hearing aid usage can slow down the decline incognitive functions.[31]
Hearing loss is responsible for causingthalamocortical dysrthymia in the brain which is a cause for several neurological disorders includingtinnitus andvisual snow syndrome.[citation needed]
Hearing loss is an increasing concern especially in aging populations. The prevalence of hearing loss increases about two-fold for each decade increase in age after age 40.[32] While the secular trend might decrease individual level risk of developing hearing loss, the prevalence of hearing loss is expected to rise due to the aging population in the US. Another concern about aging process is cognitive decline, which may progress tomild cognitive impairment and eventually dementia.[33] The association between hearing loss and cognitive decline has been studied in various research settings. Despite the variability in study design and protocols, the majority of these studies have found consistent association between age-related hearing loss and cognitive decline, cognitive impairment, and dementia.[34] The association between age-related hearing loss and Alzheimer's disease was found to be nonsignificant, and this finding supports the hypothesis that hearing loss is associated with dementia independent of Alzheimer pathology.[34] There are several hypotheses about the underlying causal mechanism for age-related hearing loss and cognitive decline. One hypothesis is that this association can be explained by common etiology or shared neurobiological pathology with decline in other physiological system.[35] Another possible cognitive mechanism emphasize on individual'scognitive load. As people developing hearing loss in the process of aging, the cognitive load demanded by auditory perception increases, which may lead to change in brain structure and eventually to dementia.[36] One other hypothesis suggests that the association between hearing loss and cognitive decline is mediated through various psychosocial factors, such as decrease insocial contact and increase insocial isolation.[35] Findings on the association between hearing loss and dementia have significant public health implication, since about 9% of dementia cases are associated with hearing loss.[37]
People with hearing loss are at a higher risk of falling. There is also a potentialdose–response relationship between hearing loss and falls—greater severity of hearing loss is associated with increased difficulties in postural control and increased prevalence of falls.[38] The underlying causal link between the association of hearing loss and falls is yet to be elucidated. There are several hypotheses that indicate that there may be a common process between decline inauditory system and increase in incident falls, driven by physiological, cognitive, and behavioral factors.[38] This evidence suggests that treating hearing loss has potential to increasehealth-related quality of life in older adults.[38]Falls have important health implications, especially for an aging population where they can lead to significant morbidity and mortality. Elderly people are particularly vulnerable to the consequences of injuries caused by falls, since older individuals typically have greater bone fragility and poorer protective reflexes.[39] Fall-related injury can also lead to burdens on the financial and health care systems.[39] In literature, age-related hearing loss is found to be significantly associated with incident falls.[40]
Hearing loss can contribute to decrease in health-related quality of life, increase in social isolation and decline in social engagement, which are all risk factors for increased risk of developing depression symptoms.[41]Depression is one of the leading causes of morbidity and mortality worldwide. In older adults, the suicide rate is higher than it is for younger adults, and more suicide cases are attributable to depression.[42] Some chronic diseases are found to be significantly associated with risk of developing depression, such ascoronary heart disease,pulmonary disease,vision loss and hearing loss.[43]
Prelingual deafness is profound hearing loss that is sustained before the acquisition of language, which can occur due to acongenital condition or through hearing loss before birth or in early infancy. Prelingual deafness impairs an individual's ability to acquire aspoken language in children, but deaf children can acquire spoken language through support from cochlear implants (sometimes combined with hearing aids).[44][45] Non-signing (hearing) parents of deaf babies (90–95% of cases) usually go with oral approach without the support of sign language, as these families lack previous experience withsign language and cannot competently provide it to their children without learning it themselves. This may in some cases (late implantation or not sufficient benefit from cochlear implants) bring the risk oflanguage deprivation for the deaf baby[46] because the deaf baby would not have a sign language if the child is unable to acquire spoken language successfully. The 5–10% of cases of deaf babies born into signing families have the potential of age-appropriate development of language due to early exposure to asign language by sign-competent parents, thus they have the potential to meet language milestones, in sign language in lieu of spoken language.[47]
Post-lingual deafness is hearing loss that is sustained after theacquisition of language, which can occur due todisease,trauma, or as a side-effect of a medicine. Typically, hearing loss is gradual and often detected by family and friends of affected individuals long before the patients themselves will acknowledge the disability.[48] Post-lingual deafness is far more common than pre-lingual deafness. Those who lose their hearing later in life, such as in late adolescence or adulthood, face their own challenges, living with the adaptations that allow them to live independently.[citation needed]
Hearing loss has multiple causes, including ageing, genetics, perinatal problems and acquired causes like noise and disease. For some kinds of hearing loss the cause may be classified asof unknown cause.[citation needed]
There is a progressive loss of ability to hear high frequencies with aging known aspresbycusis. For men, this can start as early as 25 and women at 30. Although genetically variable, it is a normal concomitant of ageing and is distinct from hearing losses caused by noise exposure, toxins or disease agents.[49] Common conditions that can increase the risk of hearing loss in elderly people arehigh blood pressure,diabetes (hearing loss in diabetes),[50] or the use of certain medications harmful to the ear.[51][52] While everyone loses hearing with age, the amount and type of hearing loss is variable.[53]
Noise-induced hearing loss (NIHL), also known asacoustic trauma, typically manifests as elevated hearing thresholds (i.e. less sensitivity or muting). Noise exposure is the cause of approximately half of all cases of hearing loss, causing some degree of problems in 5% of the population globally.[54] The majority of hearing loss is not due to age, but due to noise exposure.[55] Various governmental, industry and standards organizations set noise standards.[56] Many people are unaware of the presence of environmental sound at damaging levels, or of the level at which sound becomes harmful. Common sources of damaging noise levels include car stereos, children's toys, motor vehicles, crowds, lawn and maintenance equipment, power tools, gun use, musical instruments, and even hair dryers. Noise damage is cumulative; all sources of damage must be considered to assess risk. In the US, 12.5% of children aged 6–19 years have permanent hearing damage from excessive noise exposure.[57] The World Health Organization estimates that half of those between 12 and 35 are at risk from usingpersonal audio devices that are too loud.[11] Hearing loss in adolescents may be caused by loud noise from toys, music by headphones, and concerts or events.[58][59]
Hearing loss can be inherited. Around 75–80% of all these cases are inherited byrecessive genes, 20–25% are inherited bydominant genes, 1–2% are inherited byX-linked patterns, and fewer than 1% are inherited bymitochondrial inheritance.[60] Syndromic deafness occurs when there are other signs or medical problems aside from deafness in an individual,[60] such asUsher syndrome,Stickler syndrome,Waardenburg syndrome,Alport's syndrome, andneurofibromatosis type 2.Nonsyndromic deafness occurs when there are no other signs or medical problems associated with the deafness in an individual.[60]
Fetal alcohol spectrum disorders are reported to cause hearing loss in up to 64% of infants born toalcoholic mothers, from the ototoxic effect on the developing fetus plus malnutrition during pregnancy from the excessalcohol intake.Premature birth can be associated with sensorineural hearing loss because of an increased risk ofhypoxia,hyperbilirubinaemia, ototoxic medication and infection as well as noise exposure in the neonatal units. Also, hearing loss in premature babies is often discovered far later than a similar hearing loss would be in a full-term baby because normally babies are given a hearing test within 48 hours of birth, but doctors must wait until the premature baby is medically stable before testing hearing, which can be months after birth.[61] The risk of hearing loss is greatest for those weighing less than 1500 g at birth.
Disorders responsible for hearing loss includeauditory neuropathy,[62][63]Down syndrome,[64]Charcot–Marie–Tooth disease variant 1E,[65]autoimmune disease,multiple sclerosis,meningitis,cholesteatoma,otosclerosis,perilymph fistula,Ménière's disease, recurring ear infections, strokes,superior semicircular canal dehiscence,Pierre Robin,Treacher-Collins,Usher Syndrome,Pendred Syndrome, andTurner syndrome,syphilis,vestibular schwannoma, andviral infections such asmeasles,mumps, congenitalrubella (also called German measles) syndrome, several varieties ofherpes viruses,[66][67]HIV/AIDS,[68] andWest Nile virus.
Some medications may reversibly or irreversibly affect hearing. These medications are consideredototoxic. This includesloop diuretics such as furosemide and bumetanide,non-steroidal anti-inflammatory drugs (NSAIDs) both over-the-counter (aspirin, ibuprofen, naproxen) as well as prescription (celecoxib, diclofenac, etc.), paracetamol,quinine, andmacrolide antibiotics.[69] Others may cause permanent hearing loss.[70] The most important group is theaminoglycosides (main membergentamicin) and platinum based chemotherapeutics such ascisplatin andcarboplatin.[71][72]
In addition to medications, hearing loss can also result from specific chemicals in the environment: metals, such aslead;solvents, such astoluene (found incrude oil,gasoline[73] andautomobile exhaust,[73] for example); andasphyxiants.[74] Combined with noise, these ototoxic chemicals have an additive effect on a person's hearing loss.[74] Hearing loss due to chemicals starts in the high frequency range and is irreversible. It damages thecochlea with lesions and degrades central portions of theauditory system.[74] For some ototoxic chemical exposures, particularly styrene,[75] the risk of hearing loss can be higher than being exposed tonoise alone. The effects is greatest when the combined exposure includeimpulse noise.[76][77] A 2018 informational bulletin by the USOccupational Safety and Health Administration (OSHA) and theNational Institute for Occupational Safety and Health (NIOSH) introduces the issue, provides examples of ototoxic chemicals, lists the industries and occupations at risk and provides prevention information.[78]
There can be damage either to the ear, whether the external or middle ear, to the cochlea, or to the brain centers that process the aural information conveyed by the ears. Damage to the middle ear may include fracture and discontinuity of the ossicular chain.[79][80] Damage to the inner ear (cochlea) may be caused bytemporal bone fracture. People who sustain head injury are especially vulnerable to hearing loss or tinnitus, either temporary or permanent.[81][82]
Sound waves reach the outer ear and are conducted down the ear canal to theeardrum, causing it to vibrate. The vibrations are transferred by the 3 tiny ear bones of themiddle ear to the fluid in the inner ear. The fluid moves hair cells (stereocilia), and their movement generates nerve impulses which are then taken to the brain by thecochlear nerve.[83][84] The auditory nerve takes the impulses to the brainstem, which sends the impulses to the midbrain. Finally, the signal goes to the auditory cortex of the temporal lobe to be interpreted as sound.[85]
Hearing loss is most commonly caused by long-term exposure to loud noises, from recreation or from work, that damage the hair cells, which do not grow back on their own.[86][87][9]
Older people may lose their hearing from long exposure to noise, changes in the inner ear, changes in the middle ear, or from changes along the nerves from the ear to the brain.[88]
Identification of a hearing loss is usually conducted by a general practitionermedical doctor,otolaryngologist, certified and licensedaudiologist, school or industrialaudiometrist, or other audiometric technician. Diagnosis of the cause of a hearing loss is carried out by a specialist physician (audiovestibular physician) orotorhinolaryngologist.
Hearing loss is generally measured by playing generated or recorded sounds, and determining whether the person can hear them. Hearing sensitivity varies according to thefrequency of sounds. To take this into account, hearing sensitivity can be measured for a range of frequencies and plotted on anaudiogram. Other method for quantifying hearing loss is ahearing test using a mobile application or hearing aid application, which includes a hearing test.[89][90] Hearing diagnosis using mobile application is similar to theaudiometry procedure.[89] Audiograms, obtained using mobile applications, can be used to adjust hearing aid applications.[90] Another method for quantifying hearing loss is a speech-in-noise test. which gives an indication of how well one can understand speech in a noisy environment.[91] Otoacoustic emissions test is an objective hearing test that may be administered to toddlers and children too young to cooperate in a conventional hearing test. Auditory brainstem response testing is an electrophysiological test used to test for hearing deficits caused by pathology within the ear, the cochlear nerve and also within the brainstem.
A case history (usually a written form, with questionnaire) can provide valuable information about the context of the hearing loss, and indicate what kind of diagnostic procedures to employ. Examinations includeotoscopy,tympanometry, and differential testing with theWeber,Rinne, Bing and Schwabach tests. In case of infection or inflammation, blood or other body fluids may be submitted for laboratory analysis. MRI and CT scans can be useful to identify the pathology of many causes of hearing loss.
Hearing loss is categorized by severity, type, and configuration. Furthermore, a hearing loss may exist in only one ear (unilateral) or in both ears (bilateral). Hearing loss can be temporary or permanent, sudden or progressive. Theseverity of a hearing loss is ranked according to ranges of nominal thresholds in which a sound must be so it can be detected by an individual. It is measured indecibels of hearing loss, or dB HL. There are three maintypes of hearing loss:conductive hearing loss,sensorineural hearing loss, and mixed hearing loss.[15] An additional problem which is increasingly recognised isauditory processing disorder which is not a hearing loss as such but a difficulty perceiving sound. The shape of an audiogram shows the relativeconfiguration of the hearing loss, such as aCarhart notch for otosclerosis, 'noise' notch for noise-induced damage, high frequency rolloff for presbycusis, or a flat audiogram for conductive hearing loss. In conjunction with speech audiometry, it may indicate central auditory processing disorder, or the presence of aschwannoma or other tumor.
People withunilateral hearing loss or single-sided deafness (SSD) have difficulty in hearing conversation on their impaired side, localizing sound, and understanding speech in the presence of background noise. One reason for the hearing problems these patients often experience is due to thehead shadow effect.[92]
Idiopathic sudden hearing loss is a condition where a person as an immediate decrease in the sensitivity of theirsensorineural hearing that does not have a known cause.[93] This type of loss is usually only on one side (unilateral) and the severity of the loss varies. A common threshold of a "loss of at least 30 dB in three connected frequencies within 72 hours" is sometimes used, however there is no universal definition or international consensus for diagnosing idiopathic sudden hearing loss.[93]
It is estimated that half of cases of hearing loss are preventable.[94] About 60% of hearing loss in children under the age of 15 can be avoided.[95][2] There are a number of effective preventative strategies, including: immunization againstrubella to preventcongenital rubella syndrome, immunization againstH. influenza andS. pneumoniae to reduce cases ofmeningitis, and avoiding or protecting against excessive noise exposure.[15] TheWorld Health Organization also recommends immunization againstmeasles,mumps, andmeningitis, efforts to preventpremature birth, and avoidance of certain medication as prevention.[96]World Hearing Day is a yearly event to promote actions to prevent hearing damage.
Avoiding exposure to loud noise can help prevent noise-induced hearing loss.[97] 18% of adults exposed to loud noise at work for five years or more report hearing loss in both ears as compared to 5.5% of adults who were not exposed to loud noise at work.[98] Different programs exist for specific populations such as school-age children, adolescents and workers.[99] But the HPD (without individual selection, training andfit testing) does not significantly reduce the risk of hearing loss.[100][101] The use ofantioxidants is being studied for the prevention of noise-induced hearing loss, particularly for scenarios in which noise exposure cannot be reduced, such as during military operations.[102]
Noise is widely recognized as anoccupational hazard. In the United States, theNational Institute for Occupational Safety and Health (NIOSH) and theOccupational Safety and Health Administration (OSHA) work together to provide standards and enforcement on workplace noise levels.[103][104] Thehierarchy of hazard controls demonstrates the different levels of controls to reduce or eliminate exposure to noise and prevent hearing loss, includingengineering controls andpersonal protective equipment (PPE).[105] Other programs and initiative have been created to prevent hearing loss in the workplace. For example, theSafe-in-Sound Award was created to recognize organizations that can demonstrate results of successful noise control and other interventions.[106] Additionally, theBuy Quiet program was created to encourage employers to purchase quieter machinery and tools.[107] By purchasing less noisy power tools like those found on theNIOSH Power Tools Database and limiting exposure to ototoxic chemicals, great strides can be made in preventing hearing loss.[108]
Companies can also provide personal hearing protector devices tailored to both the worker and type of employment. Some hearing protectors universally block out all noise, and some allow for certain noises to be heard. Workers are more likely to wear hearing protector devices when they are properly fitted.[109]
Often interventions to prevent noise-induced hearing loss have many components. A 2017 Cochrane review found that stricter legislation might reduce noise levels.[110] Providing workers with information on theirsound exposure levels was not shown to decrease exposure to noise. Ear protection, if used correctly, can reduce noise to safer levels, but often, providing them is not sufficient to prevent hearing loss. Engineering noise out and other solutions such as proper maintenance of equipment can lead to noise reduction, but further field studies on resulting noise exposures following such interventions are needed. Other possible solutions include improved enforcement of existing legislation and better implementation of well-designed prevention programmes, which have not yet been proven conclusively to be effective. The conclusion of the Cochrane Review was that further research could modify what is now regarding the effectiveness of the evaluated interventions.[110]
TheInstitute for Occupational Safety and Health of the German Social Accident Insurance has created a hearing impairment calculator based on the ISO 1999 model for studyingthreshold shift in relatively homogeneous groups of people, such as workers with the same type of job. The ISO 1999 model estimates how much hearing impairment in a group can be ascribed to age andnoise exposure. The result is calculated via analgebraic equation that uses the A-weighted sound exposure level, how many years the people were exposed to this noise, how old the people are, and their sex. The model's estimations are only useful for people without hearing loss due to non-job related exposure and can be used for prevention activities.[111]
TheUnited States Preventive Services Task Force recommendsneonatal hearing screening for all newborns, as the first three years of life are believed to be the most important for language development.[8][112] Universal neonatal hearing screenings have now been widely implemented across the U.S., with rates of newborn screening increasing from less than 3% in the early 1990s to 98% in 2009.[113][114] Newborns whose screening reveals a high index of suspicion of hearing loss are referred for additional diagnostic testing with the goal of providing early intervention and access to language.[115]
TheAmerican Academy of Pediatrics advises that children should have their hearing tested several times throughout their schooling:[57]
While the American College of Physicians indicated that there is not enough evidence to determine the utility of screening in adults over 50 years old who do not have any symptoms,[116] theAmerican Language, Speech Pathology and Hearing Association recommends that adults should be screened at least every decade through age 50 and at three-year intervals thereafter, to minimize the detrimental effects of the untreated condition on quality of life.[117] For the same reason, the US Office of Disease Prevention and Health Promotion included as one ofHealthy People 2020 objectives: to increase the proportion of persons who have had a hearing examination.[118]
Management depends on the specific cause if known as well as the extent, type and configuration of the hearing loss. Sudden hearing loss due to an underlying nerve problem may be treated withcorticosteroids.[119]
Most hearing loss, that result from age and noise, is progressive and irreversible, and there are currently no approved or recommended treatments. A few specific kinds of hearing loss are amenable to surgical treatment. In other cases, treatment is addressed to underlying pathologies, but any hearing loss incurred may be permanent. Some management options includehearing aids,cochlear implants,middle ear implants,assistive technology, andclosed captioning;[9] inmovie theaters, a Hearing Impaired (HI) audio track may be available via headphones to better hear dialog.[120]
This choice depends on the level of hearing loss, type of hearing loss, and personal preference. Hearing aid applications are one of the options for hearing loss management.[90][121] For people with bilateral hearing loss, it is not clear if bilateral hearing aids (hearing aids in both ears) are better than a unilateral hearing aid (hearing aid in one ear).[9]
For people with idiopathic sudden hearing loss, different treatment approaches have been suggested that are usually based on the suspected cause of the sudden hearing loss. Treatment approaches may include corticosteroid medications, rheological drugs, vasodilators, anesthetics, and other medications chosen based on the suspected underlying pathology that caused the sudden hearing loss.[93] The evidence supporting most treatment options for idiopathic sudden hearing loss is very weak and adverse effects of these different medications is a consideration when deciding on a treatment approach.[93]
_world_map_-_DALY_-_WHO2004.svg)
no data <250 250–295 295–340 340–385 385–430 430–475 | 475–520 520–565 565–610 610–655 655–700 >700 |
Globally, hearing loss affects about 10% of the population to some degree.[54] It caused moderate to severe disability in 124.2 million people as of 2004 (107.9 million of whom are in low and middle income countries).[13] Of these 65 million acquired the condition during childhood.[15] At birth ~3 per 1000 indeveloped countries and more than 6 per 1000 indeveloping countries have hearing problems.[15]
Hearing loss increases with age. In those between 20 and 35 rates of hearing loss are 3% while in those 44 to 55 it is 11% and in those 65 to 85 it is 43%.[8]
A 2017 report by the World Health Organization estimated the costs of unaddressed hearing loss and the cost-effectiveness of interventions, for the health-care sector, for the education sector and as broad societal costs.[122] Globally, the annual cost of unaddressed hearing loss was estimated to be in the range of $750–790 billioninternational dollars.
TheInternational Organization for Standardization (ISO) developed the ISO 1999 standards for the estimation of hearing thresholds and noise-induced hearing impairment.[123] They used data from two noise and hearing study databases, one presented by Burns and Robinson (Hearing and Noise in Industry, Her Majesty's Stationery Office, London, 1970) and by Passchier-Vermeer (1968).[124] As race are some of the factors that can affect the expected distribution of pure-tone hearing thresholds several other national or regional datasets exist, from Sweden,[125] Norway,[126] South Korea,[127] the United States[128] and Spain.[129]
In the United States hearing is one of the health outcomes measure by theNational Health and Nutrition Examination Survey (NHANES), asurveyresearch program conducted by theNational Center for Health Statistics. It examineshealth andnutritional status of adults and children in theUnited States. Data from the United States in 2011–2012 found that rates of hearing loss has declined among adults aged 20 to 69 years, when compared with the results from an earlier time period (1999–2004). It also found that adult hearing loss is associated with increasing age, sex, ethnicity, educational level, and noise exposure.[130] Nearly one in four adults had audiometric results suggesting noise-induced hearing loss. Almost one in four adults who reported excellent or good hearing had a similar pattern (5.5% on both sides and 18% on one side). Among people who reported exposure to loud noise at work, almost one third had such changes.[131]
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People with extreme hearing loss may communicate throughsign languages. Sign languages convey meaning through manual communication and body language instead of acoustically conveyed sound patterns. This involves the simultaneous combination of hand shapes, orientation and movement of the hands, arms or body, and facial expressions to express a speaker's thoughts. "Sign languages are based on the idea that vision is the most useful tool a deaf person has to communicate and receive information".[132]
Deaf culture refers to a tight-knitcultural group of people whoseprimary language is signed, and who practice social and cultural norms which are distinct from those of the surrounding hearing community. This community does not automatically include all those who are clinically or legally deaf, nor does it exclude every hearing person. According to Baker and Padden, it includes any person or persons who "identifies him/herself as a member of the Deaf community, and other members accept that person as a part of the community,"[133] an example beingchildren of deaf adults with normal hearing ability. It includes the set of social beliefs, behaviors, art, literary traditions, history, values, and shared institutions of communities that are influenced by deafness and which use sign languages as the main means of communication.[134][135] Members of the Deaf community tend to view deafness as a difference in human experience rather than adisability ordisease.[136][137] When used as a cultural label especially within the culture, the worddeaf is often written with a capitalD and referred to as "big D Deaf" in speech and sign. When used as a label for theaudiological condition, it is written with a lower cased.[134][135]
There also multiple educational institutions for both deaf and Deaf people, that usually use sign language as the main language of instruction. Famous institutions includeGallaudet University and theNational Technical Institute for the Deaf in the US,[138] and theNational University Corporation of Tsukuba University of Technology in Japan.[139]
A 2005 study achieved successfulregrowth of cochlea cells in guinea pigs.[140] However, the regrowth of cochlear hair cells does not imply the restoration of hearing sensitivity, as the sensory cells may or may not make connections with neurons that carry the signals from hair cells to the brain. A 2008 study has shown that gene therapy targetingAtoh1 can cause hair cell growth and attract neuronal processes in embryonic mice. Some hope that a similar treatment will one day ameliorate hearing loss in humans.[141]
Recent research reported in 2012 achieved growth of cochlear nerve cells resulting in hearing improvements in gerbils by using stem cells.[142] Also reported in 2013 was regrowth of hair cells in deaf adult mice using a drug intervention resulting in hearing improvement.[143] TheHearing Health Foundation in the US has embarked on a project called the Hearing Restoration Project.[144] Also Action on Hearing Loss in the UK is also aiming to restore hearing.[145]
Researchers reported in 2015 that genetically deaf mice which were treated withTMC1 gene therapy recovered some of their hearing.[146][147] In 2017, additional studies were performed to treatUsher syndrome[148] and here, a recombinant adeno-associated virus seemed to outperform the older vectors.[149][150]
Besides research studies seeking to improve hearing, such as the ones listed above, research studies on the deaf have also been carried out in order to understand more about audition. Pijil and Shwarz (2005) conducted their study on the deaf who lost their hearing later in life and, hence, used cochlear implants to hear. They discovered further evidence for rate coding of pitch, a system that codes for information for frequencies by the rate that neurons fire in the auditory system, especially for lower frequencies as they are coded by the frequencies that neurons fire from the basilar membrane in a synchronous manner. Their results showed that the subjects could identify different pitches that were proportional to the frequency stimulated by a single electrode. The lower frequencies were detected when the basilar membrane was stimulated, providing even further evidence for rate coding.[151]
Over 30% of childhood hearing loss is caused by diseases such as measles, mumps, rubella, meningitis and ear infections. These can be prevented through immunization and good hygiene practices. Another 17% of childhood hearing loss results from complications at birth, including prematurity, low birth weight, birth asphyxia and neonatal jaundice. Improved maternal and child health practices would help to prevent these complications. The use of ototoxic medicines in expectant mothers and newborns, which is responsible for 4% of childhood hearing loss, could potentially be avoided.
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