How your ears work
The outer ear
Sound waves are captured by the shape of your ear and transmits them to the eardrum via the ear canal.
The middle ear
Three tiny bones and the eardrum make up the middle ear. Sound waves cause the eardrum to vibrate. The three bones or ossicles, called malleus, incus, and stapes, pass the vibration on to the inner ear.
The inner ear
Sound waves are transformed into electrical impulses. The cochlea is filled with fluid, sound waves cause this fluid to move and the movement is picked up by the sensory cells which send the electrical impulses to your brain.
Once impulses are sent to the brain, it processes the data so that we can select what is relevant to the situation and follow it.
Common causes of hearing loss
Conductive hearing loss
Conductive hearing loss can be caused by any pathology in the external ear, tympanic membrane (ear drum), middle ear, or ossicles (three bones in either middle ear ). These are all structures that help to conduct or transmit sound waves to the cochlea.
Ear wax and foreign bodies blocking the ear canal.
Inflammation of the outer ear known as otitis externa or more commonly called swimmer’s ear.
Middle ear diseases known collectively as otitis media may be referred to as an ear infection.
Tympanic membrane perforation, or a hole in your eardrum.
Cholesteatoma which is an abnormal, noncancerous skin growth that can develop in the middle ear, behind the eardrum.
Temporal bone trauma (resulting in haemotympanum or ossicular disruption).
Hereditary abnormal bone growth in the middle ear known as otosclerosis.
In many cases conductive hearing loss will resolve itself or can be treated with medicine or surgery.
Sensorineural hearing loss
Sensorineural hearing loss (SNHL) is caused by abnormalities of the cochlea, auditory nerve, or other structures that translate neural impulses to the brain. This is the most common type of permanent hearing loss. Most of the time SNHL cannot be completely resolved be medicine or surgery. Hearing aids may assist with reducing the severity and symptoms of SNHL. There are many causes of SNHL
Presbycusis which is the cumulative result of the normal ageing process on your ears.
Noise induced hearing loss caused by listening to damaging loud noises for a prolonged period, or a one-off exposure to an intensely loud sound.
Ototoxic chemicals or medications that are ‘toxic’ to the cochlea or auditory nerve, and sometimes the vestibular system.
Hearing loss that runs in the family that can start at birth or later on in life.
Injuries or operation traumas to the head.
A problem in the way the inner ear is formed.
Mixed Hearing Loss
Mixed hearing loss occurs when both conductive hearing loss and sensorineural hearing loss are present. The sensorineural component is permanent, while the conductive component can either be permanent or temporary. For example, a mixed hearing loss can occur when someone with presbycusis also has an ear infection.
Severity of hearing loss
Hearing loss is measured in decibels (dB).
The degrees of hearing loss include:
mild (26 – 40 dB) – soft sounds may be difficult to distinguish;
moderate (41 – 55 dB) – conversational speech is hard to hear, especially if there is background noise (such as a television or radio);
moderately severe (56 – 70 dB) – it is very difficult to hear ordinary speech;
severe (71 – 90 dB) – conversational speech cannot be heard; and
profound (91+ dB) – almost all sounds are inaudible.
After you have a full diagnostic hearing test your Audiologist will be able to inform you of the degree of your hearing loss. The longer your hearing loss remains unresolved, the greater the consequences are for your overall health and well being.
Do you know how healthy your hearing is?
Book a free hearing health check to find out.
Both the amount of noise and the length of time you are exposed to the noise determine its ability to damage your hearing. Noise levels are measured in decibels (dB). Sounds louder than 80 dB are considered potentially hazardous.
The World Health Organization states there is growing concern about the increasing levels of exposure to loud sounds in recreational settings such as nightclubs, discotheques, pubs, bars, cinemas, concerts, sporting events and even fitness classes.
The rising popularity of devices such as music players and smart phones, often listened to at unsafe volumes, and for prolonged periods of time, poses a serious problem of irreversible hearing loss.
Use the safe listening chart pictured as a guide to help you protect your hearing health.
What is the relationship between hearing health and dementia?
Hearing in patients with dementia is a focus of growing clinical interest. Recent evidence suggests that hearing loss may predict or accelerate cognitive decline.
Research has shown that hearing loss may decrease quality of life through social isolation, feelings of loneliness and depression, and a loss of independence. These factors in turn may increase the risk of developing dementia. Alternatively, hearing loss may place an increased load on the mental resources of your brain, as it works harder to decode and process sound if you have difficulty hearing.
Professor Gill Livingston and her colleagues from University College London published a 2017 article in The Lancet summarising 13 studies that investigated the link between hearing loss and risk of cognitive decline and dementia.
They reported hearing loss is a big but possibly modifiable risk factor for dementia and said that management of hearing loss might help ease or prevent the onset of dementia.
The research also suggests hearing is impaired in people with dementia and poor hearing is known to worsen the effects of cognitive problems.
“Communication impairments caused by hearing loss can lead to social isolation and loneliness in older adults, and epidemiologic and neuroanatomic studies have demonstrated associations between loneliness and cognitive decline or dementia,” note the researchers.
Furthermore, “studies demonstrating that under conditions where auditory perception is difficult (i.e. in the case of hearing loss), greater cognitive resources are dedicated to auditory perceptual processing, to the detriment of other cognitive processes such as working memory.”
Another researcher, Frank R. Lin, M.D., Ph.D., of The Johns Hopkins Center on Aging and Health, Baltimore, studied 1,984 older adults (with an average aged of 77 years) enrolled in a long-term observational study that began in 1997-98.
“Our results demonstrate that hearing loss is independently associated with accelerated cognitive decline and incident cognitive impairment in community-dwelling older adults,” the authors comment.
Compared to individuals with normal hearing, those individuals with a mild, moderate, and severe hearing impairment, respectively, had a 2-, 3-, and 5-fold increased risk of incident all-cause dementia over >10 years of follow-up.
It is important to remember however, that hearing loss is a modifiable risk factor, and having any form of hearing loss does not guarantee that a person will develop dementia.
More research needs to be done on the link between hearing loss and cognitive deterioration. Nonetheless, it seems very sound advice to manage your hearing loss to maintain a “healthy brain”.
Lin, Frank R. et al. “Hearing Loss and Incident Dementia.” Archives of Neurology, Volume 68.2, 2011, Pages 214–220.
Livingston, G. et al. “Dementia prevention, intervention, and care.” The Lancet, Volume 390, Issue 10113, 2017, Pages 2673-2734.
Balance and hearing
One of the most significant studies conducted to determine the connection between untreated hearing loss and falls utilised data from the 2001–2004 cycles of the National Health and Nutrition Examination Survey.
This survey has regularly collected health data from thousands of Americans since 1971. More than 2,000 survey participants between the ages of 40 to 69 had their hearing tested and responded to the question: “Have you fallen during the past year?” Researchers also tested participants’ vestibular function in order to determine if their balance was being affected by their hearing loss.
The lead researchers reported that people with mild hearing loss (25 decibels) were nearly three times as likely to have a history of falling. Every additional 10 dB of hearing loss increased the likelihood of falling by 1.4. Even after other factors (age, sex, race, cardiovascular disease and vestibular function) were considered, the findings held true.
Hearing and your heart
Poor heart health causes inadequate blood flow and blood vessel trauma to the inner ear. The inner ear is so sensitive to blood flow that disorders such as hearing loss, particularly at the lower frequencies, may be an early warning sign of cardiovascular disease.
The two-part Framingham Study^ hypothesised that low-frequency hearing loss was associated with cardiovascular disease.
Results indicated a significant association between low-frequency hearing loss and cardiovascular disease risk factors. When controlling for age, hypertension, diabetes, smoking, and hyperlipidemia, low-frequency hearing loss was significantly associated with multiple cardio and cerebrovascular disorders.
^Since 1948 this ongoing cardiovascular study has been conducted on residents of Framingham, Massachusetts, USA
Researchers have discovered a higher rate of hearing loss in people with diabetes. Using tests that measure participants’ ability to hear at the low, mid, and high-frequencies in both ears, the results indicated a link between diabetes and hearing loss at all frequencies, with a somewhat stronger association in the high-frequency range. Mild or worse hearing of low- or mid-frequency sounds was about 21 percent in 399 adults with diabetes compared to about nine percent in 4,741 adults without. Mild or greater hearing impairment at high frequencies was 54 percent in those with diabetes compared to 32 percent in those without.
Another significant study examined hearing data from participants in the National Health and Nutrition Examination Survey between 1999 and 2004 in the United States. Of the more than 5,000 individuals who took part, hearing loss appeared in 15% of those without diabetes and more than 30% in those diagnosed with diabetes. The research team’s report concluded that screening for hearing loss would allow for early medical intervention that could improve hearing for adults with diabetes.
Diabetics are 2.15 times as likely as people without the disease to have hearing loss. Broken down by age, people under 60 had 2.61 times the risk while people over 60 had 1.58 times higher risk.
Evidence exists that diabetes may lead to sensorineural hearing loss. Post-mortem studies of diabetic patients have shown evidence diabetes may lead to sensorineural hearing loss by damaging the nerves and blood vessels of the inner ear due to the pathologic changes that are associated with the condition.
Sclerosis of the internal auditory artery.
Thickened capillaries of the stria vascularis.
Atrophy of the spiral ganglion.
Demyelination of the eighth cranial nerve.
It appears the damage is more common in patients with Type 2 diabetes.
Annals of Internal Medicine. NIH Public Access. Diabetes and Hearing Impairment in the United States: Audiometric Evidence from the National Health and Nutrition Examination Surveys, 1999-2004. Kathleen E. Bainbridge, PhD, et al. 2008.
Hendricks, J. et al (2006). Progressive sensorineural hearing impairment in maternally inherited diabetes mellitus and deafness (MIDD). Otology Neurotology.27 , 6, 802-808.