Hearing loss

Hearing loss, also known as hearing impairment, is a partial or total inability to hear. A deaf person has little to no hearing. Hearing loss may occur in one or both ears.] In children, hearing problems can affect the ability to learn spoken language and in adults it can create difficulties with social interaction and at work. In some people, particularly older people, hearing loss can result in loneliness. Hearing loss can be temporary or permanent.

Hearing loss may be caused by a number of factors, including: genetics, ageing, exposure to noise, some infections, birth complications, trauma to the ear, and certain medications or toxins. A common condition that results in hearing loss is chronic ear infections. Certain infections during pregnancy, such as syphilis and rubella, may also cause hearing loss in the child. Hearing loss is diagnosed when hearing testing finds that a person is unable to hear 25 decibels in at least one ear. Testing for poor hearing is recommended for all newborns. Hearing loss can be categorized as mild (25 to 40 dB), moderate (41 to 55 dB), moderate-severe (56 to 70 dB), severe (71 to 90 dB), or profound (greater than 90 dB). There are three main types of hearing loss: conductive hearing loss, sensorineural hearing loss, and mixed hearing loss.

About half of hearing loss globally is preventable through public health measures. Such practices include immunization, proper care around pregnancy, avoiding loud noise, and avoiding certain medications. The World Health Organization recommends that young people limit the use of personal audio players to an hour a day in an effort to limit exposure to noise. Early identification and support are particularly important in children. For many hearing aids, sign language, cochlear implants and subtitles are useful. Lip reading is another useful skill some develop. Access to hearing aids, however, is limited in many areas of the world.

As of 2013 hearing loss affects about 1.1 billion people to some degree. It causes disability in 5% (360 to 538 million) and moderate to severe disability in 124 million people. Of those with moderate to severe disability 108 million live in low and middle income countries. Of those with hearing loss, it began during childhood for 65 million. Those who use sign language and are members of Deaf culture see themselves as having a difference rather than an illness. Most members of Deaf culture oppose attempts to cure deafness and some within this community view cochlear implants with concern as they have the potential to eliminate their culture. The term hearing impairment is often viewed negatively as it emphasises what people cannot do.

Definition

  • Hearing loss exists when there is diminished acuity to sounds normally heard. The terms hearing impaired or hard of hearing are usually reserved for people who have relative inability to hear sound in the speech frequencies. The severity of a hearing loss is categorized according to the increase in volume above the usual level necessary before the listener can detect it.
  • Deafness is defined as a degree of loss such that a person is unable to understand speech even in the presence of amplification. In profound deafness, even the highest intensity sounds produced by an audiometer (an instrument used to measure hearing by producing pure tone sounds through a range of frequencies) may not be detected. In total deafness, no sounds at all, regardless of amplification or method of production, are heard.
  • Speech perception – Another aspect of hearing involves the perceived clarity of a word rather than the intensity of sound made by the word. In humans, that aspect is usually measured by tests of speech discrimination. These tests measure one’s ability to understand speech, not to merely detect sound. There are very rare types of hearing loss which affect speech discrimination alone. One example is auditory neuropathy, a variety of hearing loss in which the outer hair cells of the cochlea are intact and functioning, but sound information is not faithfully transmitted to the auditory nerve and brain properly.

Use of the terms “hearing impaired”, “deaf-mute”, or “deaf and dumb” to describe deaf and hard of hearing people is discouraged by advocacy organizations as they are offensive to many deaf and hard of hearing people.

Hearing standards

Human hearing extends in frequency from 20–20,000 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 the threshold of pain. The ear does not hear all frequencies equally well; hearing sensitivity peaks around 3000 Hz. There are many qualities of human hearing besides frequency range and intensity that cannot easily be measured quantitatively. But 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.

Signs and symptoms

  • difficulty using the telephone
  • loss of directionality of sound
  • difficulty understanding speech, especially of children and women whose voices are of a higher frequency.
  • difficulty understanding speech in the presence of background noise (cocktail party effect)
  • sounds or speech becoming dull, muffled or attenuated
  • need for increased volume on television, radio, music and other audio sources

Hearing loss is sensory, but may have accompanying symptoms:

  • pain or pressure in the ears
  • a blocked feeling

There may also be accompanying secondary symptoms:

  • hyperacusis, heightened sensitivity with accompanying auditory pain to certain intensities and frequencies of sound, sometimes defined as “auditory recruitment”
  • tinnitus, ringing, buzzing, hissing or other sounds in the ear when no external sound is present
  • vertigo and disequilibrium
  • tympanophonia, abnormal hearing of one’s own voice and respiratory sounds, usually as a result of a patulous (a constantly open) eustachian tube or dehiscent superior semicircular canals
  • disturbances of facial movement (indicating a possible tumour or stroke) or in persons with Bell’s Palsy

Causes

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 as of unknown cause.

Age

There is a progressive loss of ability to hear high frequencies with aging known as presbycusis. 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. Common conditions that can increase the risk of hearing loss in elderly people are high blood pressure, diabetes or the use of certain medications harmful to the ear. While everyone loses hearing with age, the amount and type of hearing loss is variable.

Noise

Hearing loss due to noise may be temporary, called a ‘temporary threshold shift’, a reduced sensitivity to sound over a wide frequency range resulting from exposure to a brief but very loud noise like a gunshot, firecracker, jet engine, jackhammer, etc. or to exposure to loud sound over a few hours such as during a pop concert or nightclub session. Recovery of hearing is usually within 24 hours, but may take up to a week. Both constant exposure to loud sounds (85 dB(A) or above) and one-time exposure to extremely loud sounds (120 dB(A) or above) may cause permanent hearing loss.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. The National Institute for Occupational Safety and Health(NIOSH) recognizes that the majority of hearing loss is not due to age, but due to noise exposure. By correcting for age in assessing hearing, one tends to overestimate the hearing loss due to noise for some and underestimate it for others.

Noise-induced hearing loss (NIHL) typically manifests as elevated hearing thresholds (i.e. less sensitivity or muting) between 3000 and 6000  Hz, centred at 4000  Hz. As noise damage progresses, damage spreads to affect lower and higher frequencies. On an audiogram, the resulting configuration has a distinctive notch, called a ‘noise’ notch. As ageing and other effects contribute to higher frequency loss (6–8 kHz on an audiogram), this notch may be obscured and entirely disappear.

Various governmental, industry and standards organizations set noise standards.

The U.S. Environmental Protection Agency has identified the level of 70 dB(A) (40% louder to twice as loud as normal conversation; typical level of TV, radio, stereo; city street noise) for 24‑hour exposure as the level necessary to protect the public from hearing loss and other disruptive effects from noise, such as sleep disturbance, stress-related problems, learning detriment, etc. Noise levels are typically in the 65 to 75 dB (A) range for those living near airports of freeways and may result in hearing damage if sufficient time is spent outdoors.[31]

Louder sounds cause damage in a shorter period of time. Estimation of a “safe” duration of exposure is possible using an exchange rate of 3 dB. As 3 dB represents a doubling of the intensity of sound, duration of exposure must be cut in half to maintain the same energy dose. For workplace noise regulation, the “safe” daily exposure amount at 85 dB A, known as an exposure action value, is 8 hours, while the “safe” exposure at 91 dB(A) is only 2 hours. Different standards use exposure action values between 80dBA and 90dBA. Note that for some people, sound may be damaging at even lower levels than 85 dB A. Exposures to other ototoxins (such as pesticides, some medications including chemotherapy agents, solvents, etc.) can lead to greater susceptibility to noise damage, as well as causing its own damage. This is called a synergistic interaction. Since noise damage is cumulative over long periods of time, persons who are exposed to non-workplace noise, like recreational activities or environmental noise, may have compounding damage from all sources.

Some national and international organizations and agencies use an exchange rate of 4 dB or 5 dB. While these exchange rates may indicate a wider zone of comfort or safety, they can significantly underestimate the damage caused by loud noise. For example, at 100 dB (nightclub music level), a 3 dB exchange rate would limit exposure to 15 minutes; the 5 dB exchange rate allows an hour.

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. If one is exposed to loud sound (including music) at high levels or for extended durations (85 dB A or greater), then hearing loss will occur. Sound intensity (sound energy, or propensity to cause damage to the ears) increases dramatically with proximity according to an inverse square law: halving the distance to the sound quadruples the sound intensity.

In the USA, 12.5% of children aged 6–19 years have permanent hearing damage from excessive noise exposure. The World Health Organization estimates that half of those between 12 and 35 are at risk from using personal audio devices that are too loud.

Hearing loss due to noise has been described as primarily a condition of modern society. In preindustrial times, humans had far less exposure to loud sounds. Studies of primitive peoples indicate that much of what has been attributed to age-related hearing loss may be long term cumulative damage from all sources, especially noise. People living in preindustrial societies have considerably less hearing loss than similar populations living in modern society. Among primitive people who have migrated into modern society, hearing loss is proportional to the number of years spent in modern society. Military service in World War II, the Korean War, and the Vietnam War, has likely also caused hearing loss in large numbers of men from those generations, though proving that hearing loss was a direct result of military service is problematic without entry and exit audiograms.

Hearing loss in adolescents may be caused by loud noise from toys, music by headphones, and concerts or events. In 2017, the Centers for Disease Control and Prevention brought their researchers together with experts from the World Health Organization and academia to examine the risk of hearing loss from excessive noise exposure in and outside the workplace in different age groups, as well as actions being taken to reduce the burden of the condition. A summary report was published in 2018.

Genetic

Hearing loss can be inherited. Around 75–80% of all these cases are inherited by recessive genes, 20–25% are inherited by dominant genes, 1–2% are inherited by X-linked patterns, and fewer than 1% are inherited by mitochondrial inheritance.

When looking at the genetics of deafness, there are 2 different forms, syndromic and nonsyndromic. Syndromic deafness occurs when there are other signs or medical problems aside from deafness in an individual. This accounts for around 30% of deaf individuals who are deaf from a genetic standpoint. Nonsyndromic deafness occurs when there are no other signs or medical problems associated with an individual other than deafness. From a genetic standpoint, this accounts for the other 70% of cases, and represents the majority of hereditary hearing loss. Syndromic cases occur with disorders such as Usher syndrome, Stickler syndrome, Waardenburg syndrome, Alport’s syndrome, and neurofibromatosis type 2. These are diseases that have deafness as one of the symptoms or as a common feature associated with it. Many of the genetic mutations giving rise to syndromic deafness have been identified. In nonsyndromic cases, where deafness is the only finding, it is more difficult to identify the genetic mutation although some have been discovered.

  • Gene mapping has identified the genetic locations for several nonsyndromic dominant (DFNA#) and recessive (DFNB#) forms of deafness. The first gene mapped for non-syndromic deafness, DFNA1, involves a splice site mutation in the formin related homolog diaphanous 1 (DIAPH1). A single base change in a large Costa Rican family was identified as causative in a rare form of low frequency onset progressive hearing loss with autosomal dominant inheritance exhibiting variable age of onset and complete penetrance by age 30. The most common type of congenital hearing loss in developed countries is DFNB1, also known as connexin 26 deafness or GJB2-related deafness.
  • The most common dominant syndromic forms of hearing loss include Stickler syndrome and Waardenburg syndrome.
  • The most common recessive syndromic forms of hearing loss are Pendred syndrome and Usher syndrome.
  • The congenital defect microtia, deformed or unformed outer ear, can be associated with partial or complete conductive deafness, depending upon the severity of the deformity and whether the middle ear is also affected. It can also be associated with abnormalities of the inner ear giving rise to an additional sensorineural component to the hearing loss (mixed deafness).
  • Dozens of additional genes for nonsyndromic deafness have been identified.

Perinatal problems

  • Fetal alcohol spectrum disorders are reported to cause hearing loss in up to 64% of infants born to alcoholic mothers, from the ototoxic effect on the developing fetus plus malnutrition during pregnancy from the excess alcohol intake.
  • Premature birth can be associated with sensorineural hearing loss because of an increased risk of hypoxia, hyperbilirubinaemia, ototoxic medication and infection as well as noise exposure in the neonatal units. The risk of hearing loss is greatest for those weighing less than 1500 g at birth.

Disorders

  • Auditory neuropathy a disorder of poor speech perception even though the tympanic membrane, middle ear structures, and cochlear nerve are intact. People with auditory neuropathy may have normal hearing or hearing loss ranging from mild to severe.
  • Inherited disorders
    • People with Down syndrome are more likely to have hearing loss. This is usually due to middle ear effusions in childhood but towards the end of the second decade they may develop a high frequency sensorineural hearing loss which can get progressively worse with time.
    • Charcot–Marie–Tooth disease variant 1E (CMT1E) is noted for demyelinating in addition to deafness.
    • Autoimmune disease is recognized as a cause for cochlear damage. Although rare, it is possible for autoimmune processes to target the cochlea specifically as a first presentation. Granulomatosis with polyangiitis is one of the autoimmune conditions that may precipitate hearing loss. Cogan’s syndrome commonly presents with hearing loss.
    • Multiple sclerosis can have an effect on hearing as well. Multiple sclerosis, or MS, is an autoimmune disease where the immune system attacks the myelin sheath, a covering that protects the nerves. If the auditory nerve becomes damaged, the affected person will become completely deaf in one or both ears. There is no cure for MS.
  • Meningitis may damage the auditory nerve or the cochlea.
  • Cholesteatoma is a (acquired or congenital) benign collection of squamous epithelial cells within the middle ear. Acquired cholesteatomas are commonly caused by repeated middle ear infections
  • Otosclerosis is a condition that can cause fixation of the stapes (or stirrup) in the middle ear preventing its movement and causing a conductive hearing loss.
  • Perilymph fistula – a microtear in either the round or oval window (membranes separating the middle and inner ear) of the cochlea causing perilymph to leak into the middle ear. This usually occurs as a consequence of trauma, including barotrauma, and can give rise to vertigo as well as hearing loss.
  • Ménière’s disease (endolymphatic hydrops) occurs when there is an elevated pressure in the endolymph in the cochlea. Its symptoms include fluctuating low frequency hearing loss, aural fullness, tinnitus, and dizziness lasting for hours
  • Recurring ear infections or concomitant secondary infections (such as bacterial infection subsequent to viral infection) can result in hearing loss
  • Strokes – Depending on what blood vessels are affected by the stroke, one of the symptoms can be deafness
  • Superior semicircular canal dehiscence, a gap in the bone cover above the inner ear, can lead to low-frequency conductive hearing loss, autophony and vertigo.
  • Syndromic hearing loss can be either conductive or sensorineural. It occurs with abnormalities in other parts of the bodies. Examples include Pierre Robin, Treacher-Collins, Retinitis Pigmentosa, Pedreds, and Turners syndrome, among others.
  • Syphilis is commonly transmitted from pregnant women to their fetuses, and about a third of infected children will eventually become deaf.
  • Vestibular schwannoma, erroneously known as Acoustic neuromas, and other types of brain tumors can cause hearing loss by infringement of the tumor on the vestibulocochlear nerve
  • Viral infections of the ear can cause sensorineural hearing loss usually as the consequence of a labyrinthitis. The person may be generally unwell at the time.
    • Measles may cause auditory nerve damage but usually gives rise to a chronic middle ear problem giving rise to a mixed hearing loss.
    • Mumps (Epidemic parotitis) may result in profound sensorineural hearing loss (90 dB or more), unilateral (one ear) or bilateral (both ears).
    • congenital rubella (also called German measles) syndrome, can cause deafness in newborns
    • several varieties of herpes viruses that cause other diseases can also infect the ear, and can result in hearing loss: congenital infection with cytomegalovirus is responsible for deafness in newborn children and also progressive sensorineural hearing loss in childhood; herpes simplex type 1, oral herpes associated with cold sores; Epstein Barr virus that causes mononucleosis; varicella zosteroticus that causes facial paralysis (Ramsay Hunt syndrome)
    • People with HIV/AIDS may develop hearing problems due to medications they take for the disease, the HIV virus, or due to an increased rate of other infections.
    • West Nile virus, which can cause a variety of neurological disorders, can also cause hearing loss by attacking the auditory nerve.
    • Medications

      Some medications may reversibly affect hearing. These medications are considered ototoxic. This includes loop 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, and macrolide antibiotics. The link between NSAIDs and hearing loss tends to be greater in women, especially those who take ibuprofen six or more times a week. Others may cause permanent hearing loss. The most important group is the aminoglycosides (main member gentamicin) and platinum based chemotherapeutics such as cisplatin and carboplatin.

      On October 18, 2007, the U.S. Food and Drug Administration (FDA) announced that a warning about possible sudden hearing loss would be added to drug labels of PDE5 inhibitors, which are used for erectile dysfunction.

      Audiologic monitoring for ototoxicity allows for the (1) early detection of changes to hearing status presumably attributed to a drug/treatment regime so that changes in the drug regimen may be considered, and (2) audiologic intervention when handicapping hearing impairment has occurred.

      Co-administration of anti-oxidants and ototoxic medications may limit the extent of the ototoxic damage

      Chemicals

      In addition to medications, hearing loss can also result from specific chemicals in the environment: metals, such as lead; solvents, such as toluene (found in crude oil, gasoline and automobile exhaust, for example); and asphyxiants. Combined with noise, these ototoxic chemicals have an additive effect on a person’s hearing loss

      Hearing loss due to chemicals starts in the high frequency range and is irreversible. It damages the cochlea with lesions and degrades central portions of the auditory system. For some ototoxic chemical exposures, particularly styrene, the risk of hearing loss can be higher than being exposed to noise alone. The effects is greatest when the combined exposure include impulse noise.

      • Solvents
        • toluene, styrene, xylene, n-hexane, ethyl benzene, white spirits/Stoddard, carbon disulfide, jet fuel, perchloroethylene, trichloroethylene, p-xylene
      • Asphyxiants
        • carbon monoxide, hydrogen cyanide
      • Heavy metals
        • lead, mercury, cadmium, arsenic, tin-hydrocarbon compounds (trimethyltin)
      • Pesticides and herbicides – The evidence is weak regarding association between herbicides and hearing loss; hearing loss in such circumstances may be due to concommitant exposure to insecticides.
        • paraquat, organophosphates

      A 2018 informational bulletin by the US Occupational Safety and Health Administration (OSHA) and the National 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.

      Physical trauma

      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. Damage to the inner ear (cochlea) may be caused by temporal bone fracture. People who sustain head injury are especially vulnerable to hearing loss or tinnitus, either temporary or permanent.

      Pathophysiology

      Sound waves reach the outer ear and are conducted down the ear canal to the eardrum, causing it to vibrate. The vibrations are transferred by the 3 tiny ear bones of the middle 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 the cochlear nerve. 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.

      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.

      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.

      Diagnosis

      a female medical professional is seated in front of a special sound-proof booth with a glass window, controlling diagnostic test equipment. Inside the booth a middle aged man can be seen wearing headphones and is looking straight ahead of himself, not at the audiologist, and appears to be concentrating on hearing something

      An audiologist conducting an audiometric hearing test in a sound-proof testing booth

      Identification of a hearing loss is usually conducted by a general practitioner medical doctor, otolaryngologist, certified and licensed audiologist, school or industrial audiometrist, or other audiometric technician. Diagnosis of the cause of a hearing loss is carried out by a specialist physician (audiovestibular physician) or otorhinolaryngologist.

      Case history

      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. Case history will include such items as:

      • major concern
      • birth and pregnancy information
      • medical history
      • development history
      • family history
      • workplace environment
      • home environment

      Examination

      • otoscopy, visual examination of the outer ear, ear canal, eardrum, and middle ear (through the translucent eardrum) using an optical instrument inserted into the ear canal called an otoscope
      • tympanometry
      • differential testing – the Weber, Rinne, Bing and Schwabach tests are simple manual tests of auditory function conducted with a low frequency (usually 512 Hz) tuning fork that can provide a quick indication of type of hearing loss: unilateral/bilateral, conductive, or other

      Laboratory testing

      In case of infection or inflammation, blood or other body fluids may be submitted for laboratory analysis.

      Hearing tests

      Hearing loss is generally measured by playing generated or recorded sounds, and determining whether the person can hear them. Hearing sensitivity varies according to the frequency of sounds. To take this into account, hearing sensitivity can be measured for a range of frequencies and plotted on an audiogram.

      Another method for quantifying hearing loss is a speech-in-noise test. As the name implies, a speech-in-noise test gives an indication of how well one can understand speech in a noisy environment. A person with a hearing loss will often be less able to understand speech, especially in noisy conditions. This is especially true for people who have a sensorineural loss – which is by far the most common type of hearing loss. As such, speech-in-noise tests can provide valuable information about a person’s hearing ability, and can be used to detect the presence of a sensorineural hearing loss. A recently developed digit-triple speech-in-noise test may be a more efficient screening test.

      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. The test is also useful in older children and adults and is an important measure in diagnosing auditory neuropathy described above.

      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. This test can be used to identify delay in the conduction of neural impulses due to tumours or inflammation but can also be an objective test of hearing thresholds. Other electrophysiological tests, such as cortical evoked responses, can look at the hearing pathway up to the level of the auditory cortex.

      Scans

      MRI and CT scans can be useful to identify the pathology of many causes of hearing loss. They are only needed in selected cases.

      Classification

      Hearing loss is categorized by type, severity, 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.

      Severity

      The severity 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 in decibels of hearing loss, or dB HL. The measurement of hearing loss in an individual is conducted over several frequencies, mostly 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz. The hearing loss of the individual is the average of the hearing loss values over the different frequencies. Hearing loss can be ranked differently according to different organisations; and so, in different countries different systems are in use.

      Hearing loss may be ranked as slight, mild, moderate, moderately severe, severe or profound as defined below:

      • Slight: between 16 and 25 dB HL
      • Mild:
        • for adults: between 26 and 40 dB HL
        • for children: between 20 and 40 dB HL
      • Moderate: between 41 and 54 dB HL
      • Moderately severe: between 55 and 70 dB HL
      • Severe: between 71 and 90 dB HL
      • Profound: 91 dB HL or greater
      • Totally deaf: Have no hearing at all. This is called anacusis.

      The ‘Audiometric Classifications of Hearing Impairment’ according to the International Bureau Audiophonology (BIAP) in Belgium is as follows:

      • Normal or subnormal hearing: average tone loss is equal or below 20 dB HL
      • Mild hearing loss: average tone loss between 21 and 40 dB HL
      • Moderate hearing loss
        • First degree: average tone loss between 41 and 55 dB HL
        • Second degree: average tone loss between 56 and 70 dB HL
      • Severe hearing loss
        • First degree: average tone loss between 71 and 80 dB HL
        • Second degree: average tone loss between 81 and 90 dB HL
      • Very severe hearing loss
        • First degree: average tone loss between 91 and 100 dB HL
        • Second degree: average tone loss between 101 and 110 dB HL
        • Third degree: average tone loss between 111 and 119 dB HL
      • Total hearing loss or Cophosis: average tone loss is equal or more than 120 dB HL

      Hearing loss may affect one or both ears. If both ears are affected, then one ear may be more affected than the other. Thus it is possible, for example, to have normal hearing in one ear and none at all in the other, or to have mild hearing loss in one ear and moderate hearing loss in the other.

      For certain legal purposes such as insurance claims, hearing loss is described in terms of percentages. Given that hearing loss can vary by frequency and that audiograms are plotted with a logarithmic scale, the idea of a percentage of hearing loss is somewhat arbitrary, but where decibels of loss are converted via a legally recognized formula, it is possible to calculate a standardized “percentage of hearing loss”, which is suitable for legal purposes only.

      Type

      There are three main types of hearing loss, conductive hearing loss, sensorineural hearing loss. Combinations of conductive and sensorineural hearing losses are called a mixed hearing loss. An additional problem which is increasingly recognised is auditory processing disorder which is not a hearing loss as such but a difficulty perceiving sound.

      • Conductive hearing loss

      Conductive hearing loss is present when the sound is not reaching the inner ear, the cochlea. This can be due to external ear canal malformation, dysfunction of the eardrum or malfunction of the bones of the middle ear. The eardrum may show defects from small to total resulting in hearing loss of different degree. Scar tissue after ear infections may also make the eardrum dysfunction as well as when it is retracted and adherent to the medial part of the middle ear.

      Dysfunction of the three small bones of the middle ear – malleus, incus, and stapes – may cause conductive hearing loss. The mobility of the ossicles may be impaired for different reasons including a boney disorder of the ossicles called otosclerosis and disruption of the ossicular chain due to trauma, infection or ankylosis may also cause hearing loss.

      • Sensorineural hearing loss

      Sensorineural hearing loss is one caused by dysfunction of the inner ear, the cochlea or the nerve that transmits the impulses from the cochlea to the hearing centre in the brain. The most common reason for sensorineural hearing loss is damage to the hair cells in the cochlea. Depending on the definition it could be estimated that more than 50% of the population over the age of 70 has impaired hearing.

      • Central deafness

      Damage to the brain can lead to a central deafness. The peripheral ear and the auditory nerve may function well but the central connections are damaged by tumour, trauma or other disease and the patient is unable to process speech information.

      • Mixed hearing loss

      Mixed hearing loss is a combination of conductive and sensorineural hearing loss. Chronic ear infection (a fairly common diagnosis) can cause a defective ear drum or middle-ear ossicle damages, or both. In addition to the conductive loss, a sensory component may be present.

      • Central auditory processing disorder

      This is not an actual hearing loss but gives rise to significant difficulties in hearing. One kind of auditory processing disorder is King-Kopetzky syndrome, which is characterized by an inability to process out background noise in noisy environments despite normal performance on traditional hearing tests. An auditory processing disorders is sometimes linked to language disorders in persons of all ages.

      Configuration

      The shape of an audiogram shows the relative configuration of the hearing loss, such as a Carhart 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 a schwannoma or other tumor. There are four general configurations of hearing loss:

      1. Flat: thresholds essentially equal across test frequencies.

      2. Sloping: lower (better) thresholds in low-frequency regions and higher (poorer) thresholds in high-frequency regions.

      3. Rising: higher (poorer) thresholds in low-frequency regions and lower (better) thresholds in higher-frequency regions.

      4. Trough-shaped (“cookie-bite” or “U” shaped): greatest hearing loss in the mid-frequency range, with lower (better) thresholds in low- and high-frequency regions.

      Unilateral and bilateral

      People with unilateral hearing loss or single-sided deafness (SSD) have difficulty in:

      • hearing conversation on their impaired side
      • localizing sound
      • understanding speech in the presence of background noise.

      In quiet conditions, speech discrimination is approximately the same for normal hearing and those with unilateral deafness; however, in noisy environments speech discrimination varies individually and ranges from mild to severe.

      One reason for the hearing problems these patients often experience is due to the head shadow effect. Newborn children with no hearing on one side but one normal ear could still have problems. Speech development could be delayed and difficulties to concentrate in school are common. More children with unilateral hearing loss have to repeat classes than their peers. Taking part in social activities could be a problem. Early aiding is therefore of utmost importance.

      Prevention

      It is estimated that half of cases of hearing loss are preventable. About 60% of hearing loss in children under the age of 15 can be avoided. A number of preventative strategies are effective including: immunization against rubella to prevent congenital rubella syndrome, immunization against H. influenza and S. pneumoniae to reduce cases of meningitis, and avoiding or protecting against excessive noise exposure. The World Health Organization also recommends immunization against measles, mumps, and meningitis, efforts to prevent premature birth, and avoidance of certain medication as prevention.

      Noise exposure is the most significant risk factor for noise-induced hearing loss that can be prevented. Different programs exist for specific populations such as school-age children, adolescents and workers. Education regarding noise exposure increases the use of hearing protectors. The use of antioxidants 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.

      Workplace noise regulation

      Noise is widely recognized as an occupational hazard. In the United States, the National Institute for Occupational Safety and Health (NIOSH) and the Occupational Safety and Health Administration (OSHA) work together to provide standards and enforcement on workplace noise levels. The hierarchy of hazard controls demonstrates the different levels of controls to reduce or eliminate exposure to noise and prevent hearing loss, including engineering controls and personal protective equipment (PPE). Other programs and initiative have been created to prevent hearing loss in the workplace. For example, the Safe-in-Sound Award was created to recognize organizations that can demonstrate results of successful noise control and other interventions. Additionally, the Buy Quiet program was created to encourage employers to purchase quieter machinery and tools. By purchasing less noisy power tools like those found on the NIOSH Power Tools Database and limiting exposure to ototoxic chemicals, great strides can be made in preventing hearing loss.

      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.

      Often interventions to prevent noise-induced hearing loss have many components. A 2017 Cochrane review found that stricter legislation might reduce noise levels. Providing workers with information on their noise 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.

      Screening

      The United States Preventive Services Task Force recommends screening for all newborns.

      The American Academy of Pediatrics advises that children should have their hearing tested several times throughout their schooling:

      • When they enter school
      • At ages 6, 8, and 10
      • At least once during middle school
      • At least once during high school

      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, the American Language, Speech Pathology and Hearing Association recommends that adults should be screened at least every decade through age 50 and at 3-year intervals thereafter, to minimize the detrimental effects of the untreated condition on quality of life. For the same reason, the US Office of Disease Prevention and Health Promotion included as one of Healthy People 2020 objectives: to increase the proportion of persons who have had a hearing examination.

      Treatment

      Treatment depends on the specific cause if known as well as the extent, type and configuration of the hearing loss. Most hearing loss, that resulting from age and noise, is progressive and irreversible, and there are currently no approved or recommended treatments; management is by hearing aid. 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.

      There are a number of devices that can improve hearing in those who are deaf or hard of hearing or allow people with these conditions to manage better in their lives.

      Hearing aids

      Hearing aids are devices that work to improve the hearing and speech comprehension of those with hearing loss. They work by magnifying the sound vibrations in the ear so that one can understand what is being said around them. Hearing aids have been shown to have a large beneficial effect in helping adults with mild to moderate hearing loss take part in everyday situations, and a smaller beneficial effect in improving physical, social, emotional and mental well-being in these people. Some people feel as if they cannot live without one because they say it is the only thing that keeps them engaged with the public. Conversely, there are many people who choose not to wear their hearing aids for a multitude of reasons. Up to 40% of adults with hearing aids for hearing loss fail to use them, or do not use them to their full effect. There are a number of reasons for this, stemming from factors such as: the aid amplifying background noises instead of the sounds they intended to hear; issues with comfort, care, or maintenance of the device; aesthetic factors; financial factors; and personal preference for quietness.

      There is little evidence that interventions to encourage the regular use of hearing aids, (e.g. improving the information given to people about how to use hearing aids), increase daily hours of hearing aid use, and there is currently no agreed set of outcome measures for assessing this type of intervention.

      Assistive devices

      Many deaf and hard of hearing individuals use assistive devices in their daily lives:

      • Individuals can communicate by telephone using telephone typewriters (TTY). Other common names are textphone, minicom and telecommunications device for the deaf (TDD). These devices look like typewriters or word processors and transmit typed text over regular telephone lines. This allows communication through visual messaging. TTYs can transmit messages to individuals who don’t have TTY by using the National Relay service which is an operator that acts as a messenger to each caller. For mobile phones, software apps are available to provide TDD/textphone functionality on some carriers/models to provide 2-way communications.
      • There are several new telecommunications relay service technologies including IP Relay and captioned telephone technologies. A deaf or hard of hearing person can communicate over the phone with a hearing person via a human translator. Phone captioning is a service in which a hearing person’s speech is captioned by a third party, enabling a deaf or hard of hearing person to conduct a conversation with a hearing person over the phone. Wireless, Internet and mobile phone/SMS text messaging are beginning to take over the role of the TDD.
      • Real-time text technologies, involving streaming text that is continuously transmitted as it is typed or otherwise composed. This allows conversational use of text. Software programs are now available that automatically generate a closed-captioning of conversations. Examples include discussions in conference rooms, teleconference calls, classroom lectures, and/or religious services.
      • Instant messaging software.
      • Videophones and similar video technologies can be used for distance communication using sign language. Video conferencing technologies permit signed conversations as well as permitting a sign language–English interpreter to voice and sign conversations between a deaf or hard of hearing person and that person’s hearing party, negating the use of a TTY device or computer keyboard.
      • Video relay service and video remote interpreting (VRI) services also use a third-party telecommunication service to allow a deaf or hard-of-hearing person to communicate quickly and conveniently with a hearing person, through a sign language interpreter.
      • Hearing dogs are a specific type of assistance dog specifically selected and trained to assist the deaf and hard of hearing by alerting their handler to important sounds, such as doorbells, smoke alarms, ringing telephones, or alarm clocks.
      • The advent of the Internet’s World Wide Web and closed captioning has given the deaf and hard of hearing unprecedented access to information. Electronic mail and online chat have reduced the need for deaf and hard-of-hearing people to use a third-party Telecommunications Relay Service to communicate with the hearing and other deaf people.
      • A person with hearing loss cannot always hear the phone or distinguish their own ringtone from another. A signaling transmitter can be attached to a phone that will cause a light or a vibration device to activate. Transmitters can also be used to activate visual cues to represent fire alarms.
      • Individuals with hearing loss require phones with amplifiers that have a higher power of amplification when compared to a regular phone. The Hearing Aid Telephone Interconnect System is a hands free amplification system which allows people to amplify sound when using telephones, cell phones, computer and pay phones by way of the attachment of a portable unit.

      Wireless hearing aids

      A wireless device has two main components: a transmitter and a receiver. The transmitter broadcasts the captured sound, and the receiver detects the broadcast audio and enables the incoming audio stream to be connected to accommodations such as hearing aids or captioning systems.

      Three types of wireless systems are commonly used: FM, audio induction loop, and InfraRed. Each system has advantages and benefits for particular uses. FM systems can be battery operated or plugged into an electrical outlet. FM system produce an analog audio signal, meaning they have extremely high fidelity. Many FM systems are very small in size, allowing them to be used in mobile situations. The audio induction loop permits the listener with hearing loss to be free of wearing a receiver provided that the listener has a hearing aid or cochlear implant processor with an accessory called a “telecoil”. If the listener does not have a telecoil, then he or she must carry a receiver with an earpiece. As with FM systems, the infrared (IR) system also requires a receiver to be worn or carried by the listener. An advantage of IR wireless systems is that people in adjoining rooms cannot listen in on conversations, making it useful for situations where privacy and confidentiality are required. Another way to achieve confidentiality is to use a hardwired amplifier, which contains or is connected to a microphone and transmits no signal beyond the earpiece plugged directly into it.

      Surgical

      Illustration of a cochlear implant

      There is no treatment, surgical or otherwise, for sensorineural hearing loss due to the most common causes (age, noise, and genetic defects). For a few specific conditions, surgical intervention can provide a remedy:

      • surgical correction of superior canal dehiscence
      • myringotomy, surgical insertion of drainage ventilation tubes in the tympanic membrane. Such placement is usually temporary until the underlying pathology (infection or other inflammation) can be resolved.
      • radiotherapy or surgical excision of vestibular schwannoma or acoustic neuroma, though, in most cases, it is unlikely that hearing will be preserved
      • Stapedectomy and stapedotomy for otosclerosis – replacement or reshaping of the stapes bone of the middle ear can restore hearing in cases of conductive hearing loss

      Surgical and implantable hearing aids are an alternative to conventional external hearing aids. If the ear is dry and not infected, an air conduction aid could be tried; if the ear is draining, a direct bone conduction hearing aid is often the best solution. If the conductive part of the hearing loss is more than 30–35 dB, an air conduction device could have problems overcoming this gap. A bone-anchored hearing aid could, in this situation, be a good option. The active bone conduction hearing implant Bonebridge (a product of MED-EL corporation) is also an option. This implant is invisible under the intact skin and therefore minimises the risk of skin irritations.

      Cochlear implants improve outcomes in people with hearing loss in either one or both ears. They work by artificial stimulation of the cochlear nerve by providing an electric impulse substitution for the firing of hair cells. They are expensive, and require programming along with extensive training for effectiveness.

      Cochlear implants as well as bone conduction implants can help with single sided deafness. Middle ear implants or bone conduction implants can help with conductive hearing loss.

      People with cochlear implants are at a higher risk for bacterial meningitis. Thus, meningitis vaccination is recommended. People who have hearing loss, especially those who develop a hearing problem in childhood or old age, may need support and technical adaptations as part of the rehabilitation process. Recent research shows variations in efficacy but some studies show that if implanted at a very young age, some profoundly impaired children can acquire effective hearing and speech, particularly if supported by appropriate rehabilitation.

      Classroom

      For a classroom setting, children with hearing loss often benefit from direct instruction and communication. Optimally children with hearing loss will be mainstreamed in a typical classroom and receive supportive services. One such is to sit as close to the teacher as possible improves the student’s ability to hear the teacher’s voice and to more easily read the teacher’s lips. When lecturing, teachers can help the student by facing them and by limiting unnecessary noise in the classroom. In particular, the teacher can avoid talking when their back is turned to the classroom, such as while writing on a whiteboard.

      Some other approaches for classroom accommodations include pairing deaf or hard of hearing students with hearing students. This allows the deaf or hard of hearing student to ask the hearing student questions about concepts that they have not understood. The use of CART (Communication Access Real Time) systems, where an individual types a captioning of what the teacher is saying, is also beneficial. The student views this captioning on their computer. Automated captioning systems are also becoming a popular option. In an automated system, software, instead of a person, is used to generate the captioning. Unlike CART systems, automated systems generally do not require an Internet connection and thus they can be used anywhere and anytime. Another advantage of automated systems over CART is that they are much lower in cost. However, automated systems are generally designed to only transcribe what the teacher is saying and to not transcribe what other students say. An automated system works best for situations where just the teacher is speaking, whereas a CART system will be preferred for situations where there is a lot of classroom discussion.

      For those students who are completely deaf, one of the most common interventions is having the child communicate with others through an interpreter using sign language.

      Epidemiology

      Disability-adjusted life year for hearing loss (adult onset) per 100,000 inhabitants in 2004.

      Globally, hearing loss affects about 10% of the population to some degree. 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). Of these 65 million acquired the condition during childhood. At birth ~3 per 1000 in developed countries and more than 6 per 1000 in developing countries have hearing problems.

      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%.

      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. Globally, the annual cost of unaddressed hearing loss was estimated to be in the range of $750–790 billion.

  • reference:

 

https://en.wikipedia.org/wiki/Hearing_losshttps://en.wikipedia.org/wiki/Hearing_loss

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