Hearing loss

Hearing loss is a partial or total inability to hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to acquire spoken language. In adults, it can create difficulties with social interaction and at work. Hearing loss can be temporary or permanent. Hearing loss related to age usually affects both ears and is due to cochlear hair cell loss. In some people, particularly older people, hearing loss can result in isolation and loneliness.
Hearing loss may be caused by a number of factors, including: genetics, ageing, exposure to noise, some infections, birth complications, trauma to the ear or brain, and certain medications or toxins. A common condition that results in hearing loss is chronic ear infections. Certain infections during pregnancy, such as cytomegalovirus, 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 minimal/slight, mild, moderate, moderate-severe, severe, or profound. 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 exposure to loud sounds and the use of personal audio players to an hour a day to limit noise exposure. 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.

Access and affordability

Access to hearing aids and hearing care varies widely by country, with affordability often cited as a major barrier to treatment. In New Zealand, public funding schemes provide partial or full subsidies for hearing aids depending on eligibility criteria, such as age, severity of hearing loss, and financial need.
To further improve access, some providers in New Zealand, such as Resonate Health, have introduced subscription-based hearing aid models. These typically bundle device costs, servicing, and follow-up care into a monthly fee, reducing the upfront cost of treatment.
As of 2013, hearing loss affects about 1.1 billion people to some degree. It causes disability in about 466 million people, 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 may see themselves as having a difference rather than a disability. Many members of Deaf culture reject cochlear implants and some within this community view them with concern as they have the potential to eliminate their culture.

Definition

Hearing loss is defined as diminished acuity to sounds which would otherwise be heard normally. The terms hearing impaired or hard of hearing are usually reserved for people who have a relative inability to hear sound in the speech frequencies. Hearing loss occurs when sound waves enter the ears and damage the sensitive tissues The severity of hearing loss is categorized according to the increase in intensity of sound above the usual level required for the listener to 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 may not be detected. In total deafness, no sounds at all, regardless of amplification or method of production, can be heard.
Speech perception is another aspect of hearing which involves the perceived clarity of a word rather than the intensity of sound made by the word. In humans, this is usually measured with speech discrimination tests, which measure not only the ability to detect sound, but also the ability to understand speech. There are very rare types of hearing loss that 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 by the auditory nerve to the brain.

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.

Hearing standards

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 the 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 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. Due to the cumulative impact of age and exposure to noise and other acoustic insults, 'typical' hearing may not be normal.

Signs and symptoms

The presentation is as follows:

difficulty using the telephone
loss of sound localization
difficulty understanding speech, especially of children and women whose voices are of a higher frequency.
difficulty understanding speech in the presence of background noise
sounds or speech sounding 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, also known as autophonia, abnormal hearing of one's own voice and respiratory sounds, usually as a result of a patulous eustachian tube or dehiscent superior semicircular canals
disturbances of facial movement or in persons with Bell's palsy
Complications

Hearing loss is associated with Alzheimer's disease and dementia. The risk increases with the degree of hearing loss. A systematic review and meta analysis assessed the link between hearing loss and dementia subtypes. Hearing loss was linked to an increased risk of mild to severe cognitive problems, including mild cognitive impairment and Alzheimer's disease. Hearing loss was not linked to an increased risk of vascular dementia. There are several hypotheses, including cognitive resources being redistributed to hearing and social isolation from hearing loss, having a negative effect. According to preliminary data, hearing aid usage can slow down the decline in cognitive functions.
Hearing loss is responsible for causing thalamocortical dysrhythmia in the brain, which is a cause for several neurological disorders, including tinnitus and visual snow syndrome.

Cognitive decline

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. 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 the aging process is cognitive decline, which may progress to mild cognitive impairment and eventually dementia. 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 a consistent association between age-related hearing loss and cognitive decline, cognitive impairment, and dementia. The association between age-related hearing loss and Alzheimer's disease was found to be nonsignificant. This finding supports the hypothesis that hearing loss is associated with dementia independent of Alzheimer's pathology. 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. Another possible cognitive mechanism emphasize on individual's cognitive load. As people develop hearing loss with aging, the cognitive load demanded by auditory perception increases, which may lead to changes in brain structure and eventually to dementia. One other hypothesis suggests that the association between hearing loss and cognitive decline is mediated through various psychosocial factors, such as decrease in social contact and increase in social isolation. Findings on the association between hearing loss and dementia have significant public health implications, since about 9% of dementia cases are associated with hearing loss.