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.
Genetics, aging, exposure to noise, some infections, birth complications, trauma to the ear, certain medications or toxins.
Conductive, sensorineural, and mixed hearing loss, central auditory dysfunction
Signs and symptoms
Here are some signs and symptoms of deafness.
- 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, also known as autophonia, 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.
Let’s take a look at some of the major causes of deafness. We should learn one or two lessons:
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 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.
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.
Note that for some people, sound may be damaging at even lower levels than 85 dB A.
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.
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 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.
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.
Here are chemicals that could damage your hearing according to three classification; solvents, asphyxiants and heavy metals
toluene, styrene, xylene, n-hexane, ethyl benzene, white spirits/Stoddard, carbon disulfide, jet fuel, perchloroethylene, trichloroethylene, p-xylene
carbon monoxide, hydrogen cyanide
lead, mercury, cadmium, arsenic, tin-hydrocarbon compounds (trimethyltin)
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.