Hearing impairment, deafness, or hearing loss refers to the inability to hear things, either totally or partially. Symptoms may be mild, moderate, severe or profound. A patient with mild hearing impairment may have problems understanding speech, especially if there is a lot of noise around, while those with moderate deafness may need a hearing aid. Some people are severely deaf and depend on lip-reading when communicating with others.
People who are profoundly deaf can hear nothing at all. In order to communicate spontaneously and rapidly with people, they are totally reliant on lip-reading and/or sign language. People who are born deaf find lip-reading much harder to learn compared to those who became hearing impaired after their had learnt to communicate orally (with sounds).
Some diseases or circumstances can cause deafness, including:
Sickle cell disease
AIDS - offspring of mothers who had AIDS during pregnancy have a much higher risk of being deaf by the age of 16 years
Diabetes - studies have shown that up to 40% of diabetes patients suffer from some kind of hearing loss
Tuberculosis (TB), experts believe that the medication, streptomycin, used to treat TB may be the key risk factor
Hypothyroidism - and underactive thyroid gland
Second hand smoke exposure can increase hearing loss risk in teenagers
Many people globally have untreated hearing loss. It is estimated that 23 million Americans live with untreated impaired hearing.
What is the difference between hearing loss and deafness?
Hearing loss refers to a diminished ability to hear sounds like other people do, while deafness refers to the inability to understand speech through hearing even when sound is amplified. Profound deafness means the person cannot hear anything at all; they are unable to detect sound, even at the highest volume possible.
Degree of hearing impairment - a person's severity of hearing impairment is categorized by how much louder than 'usual levels' sound volumes need to be set at before they can detect a sound.
Degree of deafness - any degree of deafness means the person cannot understand speech through hearing at any level of amplification. If a person is profoundly deaf, they cannot detect sounds at any volume. Some people define profoundly deaf and totally deaf in the same way, while others say totally deaf is the end of the hearing spectrum.
According to Medilexicon's medical dictionary:
'A general term for inability to hear.'
Hearing impairment is:
'A reduction in the ability to perceive sound; may range from slight inability to complete deafness.'
How do we hear things?
Sound waves enter the ear, go down the ear canal (auditory), and hit the eardrum, which vibrates. The vibrations from the eardrum pass to the three ossicles (bones called the malleus (hammer), incus (anvil) and stapes) in the middle ear. These occicles amplify the vibrations, which are then picked up by small hair-like cells in the cochlea; they move as the vibrations hit them, the movement data is sent through the auditory never to the brain. The brain processes the data, which we interpret as sound.
Three types of hearing loss
Conductive hearing loss - this means that the vibrations are not passing through from the outer ear to the inner ear, specifically the cochlea. It can be due to an excessive build-up of earwax, glue ear, an ear infection with inflammation and fluid buildup, a perforated eardrum, or a malfunction of the ossicles (bones in the middle ear). Also, the eardrum may be defective.
Ear infections can leave scar tissue which damages the functioning of the ear drum.
The ossicles may be impaired due to infection, trauma, or their fusing together (ankylosis).
Sensorineural hearing loss - hearing loss is caused by dysfunction of the inner ear, the cochlea, auditory nerve, or brain damage. Usually, this kind of hearing loss is due to damage of the hair cells in the cochlea. As humans get older, the hair cells lose some of their function, and our hearing gets worse. In Western Europe and North America it is estimated that over half of all people over 70 years of age have hearing impairment caused by degenerated hair cells in the cochlea.
Long-term exposure to loud noises, especially high frequency sounds, is another common reason for hair cell damage. Damaged hair cells cannot be replaced. Currently, research is looking into using stem cells to grow new ones.
Sensorineural total deafness may be due to birth defects, inner ear infections, or head trauma. If the ear drum and middle ear are functioning properly, patients may benefit from a cochlear implant - a thin electrode is inserted in the cochlea, it stimulates electricity through a tiny microprocessor which is placed under behind the ear, under the skin.
Mixed hearing loss - this is a combination of conductive and sensorineural hearing loss. Long-term ear infections can damage both the ear drum as well as the ossicles. Sometimes, surgical intervention may restore hearing, but it does not always work.
What is prelingual deafness?
Prelingual deafness refers to the inability to hear properly or at all before the patient learnt how to utter or understand speech. In such cases the individual was born with a congenital condition or lost their hearing very early in life, during infancy. People with prelingual deafness have never acquired speech with sound.
In the majority of cases, people with prelingual deafness have hearing parents and siblings, and were born into families who did not know sign language. Consequently, they also tend to have slow language development. The very few who were born into signing families tend not to have delays in language development.
If cochlear implants are placed in prelingual deaf children before they are four years old, they will usually acquire oral language successfully.
Oral language and the ability to use social cues are very closely interrelated. That is why children with hearing loss, especially those with severe symptoms, may not only experience delayed language development, but their social development will take longer too. Consequently, prelingual deaf children can become socially isolated, unless they attend a school with other prelingual deaf children which has a well run special needs department.
Children who identify with a 'Deaf sub-culture', or those who learnt how to use sign language, may not feel isolated. However, some kids might if their parents have not learnt sign language.
A prelingual deaf child whose parents and other family members encourage them to the learn social skills acquired and used by hearing children are less likely to experience social isolation.
There are cases of profoundly deaf children who find themselves in no-man's land. They are on the outer fringes of their hearing peers' social circles, while at the same time are not fully accepted by totally deaf peers because they are not fluent in sign language.
What is post-lingual deafness?
Most people with some kind of hearing loss have post-lingual deafness. They had acquired spoken language before their hearing was diminished. Losing their sense of hearing may have been caused by a medication side-effect, trauma, infection, or a disease.
In most cases, the person lost their hearing gradually; household members, friends and teachers may have noticed something was wrong before they themselves acknowledged the disability. Depending on the severity of hearing loss, the patient may have had to use hearing aids, had a cochlear implant inserted, or learnt how to lip-read.
People who experience hearing loss face different challenges, depending on when it occurred and how long it took to develop. They have to become familiar with new equipment, perhaps undergo surgery, learn sign language and lip reading, and use various communication devices. A feeling of isolation is a common problem, which can sometimes lead to depression and loneliness; add to that the process of coming to terms with a disability. It is also a challenge for household members, loved ones and close friends, who have to adapt to the person's hearing loss.
Miscommunication can place a strain on relationships, a strain not only for the person with the hearing impairment, but also people around them. If the hearing loss is gradual and has not yet been diagnosed, family members may mistakenly believe that the patient is becoming more distant.
What is unilateral and bilateral deafness?
Unilateral deafness (single-sided deafness or SDD) refers to just one ear, while bilateral means a hearing impairment in both.
People with unilateral hearing impairment may find it hard to carry on a conversation if the other person is on their 'deaf' side. Pinpointing where a sound is coming from may be more difficult, compared to those who can hear well with both ears. Understanding what others are saying when there is a lot of noise about may be hard.
When there is no background noise, or very little, a person with unilateral deafness has virtually the same aural communicative abilities as somebody with normal hearing in both ears.
Babies born with unilateral deafness tend to have speech developmental delays. They may find it harder to concentrate when they go to school. Social activities may be more challenging than it is for children with no hearing problems.
What are the signs and symptoms of hearing impairment?
A symptom is something only the patient can feel, and describes to a doctor, nurse or somebody else, such as a pain, dizziness, ringing in the ears, or fatigue. A sign is something the doctor, nurse or somebody else might detect, apart from the sufferer, examples include a rash, swelling, bleeding, or bruising.
The symptoms associated with hearing impairment depend on its cause; some people are born without being able to hear, others suddenly become deaf due to an accident or illness. A buildup of earwax can cause sudden hearing loss.. We all lose a certain amount of hearing during late-middle and old age. In most cases, deafness symptoms progress gradually over time.
Some conditions may have hearing loss as one of a number of symptoms, such as tinnitus or stroke.
Hearing impairment in babies - the following signs may indicate a hearing problem (but not always):
Before the age of four months, the baby does not turn his/her head towards a noise
By the age of 12 months, the baby still does not utter a single word
The baby does not appear to be startled by a loud noise
The baby responds to you when he/she can see you, but much less so (or not at all) when you are out of sight and call out their name
The baby seems to be aware of some sounds only
Hearing impairment in toddlers and children
The child is behind the others of his/her age in oral communication
The child keeps saying 'What?' or 'Pardon?'
The child talks in a very loud voice, and tends to produce louder-than-normal noises
When the child speaks, his/her utterances are not clear
There are four levels of deafness (possibly 5 in some countries), they are:
Mild deafness or mild hearing impairment - the patient can only detect sounds from between 25 to 29 decibels (dB). They may find it hard to understand everything other people are saying, especially if there is a lot of background noise.
Moderate deafness or moderate hearing impairment - the patient can only detect sounds from between 40dB and 69dB. Following a conversation just from hearing is very difficult without using a hearing aid.
Severe deafness - the person only hears sounds above 70db to 89dB. A severely deaf person must either lip-read or use sign language in order to communicate, even if they have a hearing aid.
Profound deafness - anybody who cannot hear a sound below 90dB is profoundly deaf; some profoundly deaf people cannot hear anything at all, at any level of decibels. Communication is done with sign language and/or lip-reading.
Obviously, if the hearing impaired deaf person can read and write, they may also communicate by reading and writing.
How is deafness diagnosed?
Patients who suspect something is wrong with their hearing will usually go and see their GP (general practitioner, primary care physician) initially. The doctor will talk to the patient and ask several questions regarding the symptoms, when they started, whether or not they have gotten worse, whether there is any pain, etc.
A physical examination - the doctor will look into the patient's ear using an otoscope (auriscope); an instrument with a light at the end. The following may be detected during the examination:
A blockage caused by a foreign object
A collapsed ear drum
An accumulation of earwax
An infection in the ear canal
An infection in the middle ear (if the ear drum bulges)
Cholesteatoma - skin growth behind the eardrum, in the middle ear
Fluid in the ear canal
There is a hole in the ear drum (perforated ear drum)
Doctors may ask questions regarding the patients hearing, which will probably be similar to the ones below:
Do you often find yourself asking people to repeat what they said?
Do you find it hard to understand people on the telephone?
Does the doorbell ring and you did not hear it? If so, does this happen frequently?
When you chat to people face-to-face, do you have to focus carefully?
Has anybody ever mentioned to you that you might have a problem with your hearing?
Do you find more people mumble today than they used to?
When you hear a sound, do you often find it hard to determine where it is coming from
When several people are talking, do you find it hard to understand what one of them is telling you?
Are you often told that the TV, radio or any sound-producing device is too loud?
Do you find the speech of men easier to understand than women's or children's?
Are you in a noisy environment for a good proportion of each day?
Have you often found yourself misunderstanding what other people say to you?
Do you hear rushing, hissing or ringing sounds?
Do you avoid group conversations?
Anybody who answers 'yes' to most of the above questions should see their doctor and have their hearing checked.
General Screening test - the GP may ask the patient to cover one ear and describe how well they hear words uttered at different volumes, as well as checking sensitivity to other sounds.
If your primary care physician suspects the patient has a hearing problem, they will probably be referred to a specialist, either an ENT (ear, nose and throat) specialist (otolaryngologist) or an audiologist.
Further tests will be carried out, including:
A tuning fork test, also known as The Rinne test. This test may have been done by the GP. A tuning fork is a metal instrument with two prongs that produces a sound when it is truck. Simple tuning fork tests may help the doctor detect whether there is any hearing loss, and where the problem is.
A tuning fork is vibrated (512 Hz) and placed against the mastoid bone. The patient is asked to indicate when he/she no longer hears any sound. The fork, which is still vibrating is then place 1 to 2 cm from the auditory canal; the patient is asked whether he/she can hear the fork. As air conduction is greater than bone conduction, the patient should say 'yes'. If they say 'no' at this point, it means that their bone conduction is superior to their air conduction, meaning there is a problem with sound waves getting to the cochlea via the ear canal.
A Rinnie test uses a tuning fork to determine where the hearing problem is located
Audiometer tests - the patient wears earphones, sounds are directed into each ear at a time. A range of sounds at various tones are presented to the patient who has to signal each time a sound is heard. Each tone is presented at various volumes so that the audiologist can determine at which point the sound at that tone is no longer detected. The same is done with words, the audiologists presents words at various tones and decibel levels.
Bone oscillator test - used to find out how well vibrations are passed through the ossicles, the three bones in the inner ear. A bone oscillator is placed against the mastoid (bone behind the year). The aim is ultimately to see how well the auditory nerve is working.
Routine screening of children - the American Academy of Pediatrics recommends that children have their hearing tests when they start school, then at 6, 8, and 10 years of age, at least once when they are in middle school and once during high school.
Testing newborns - he Otoacoustic Emissions (OAE) test involves inserting a small probe into the outer year; it is usually done while the baby is asleep. The probe emits sounds and checks for 'echo' sounds bouncing back from the ear (otoacoustic emission).
A saliva test can detect the presence of CMV (cytomegalovirus) infection in babies. CMV can cause hearing loss in infants.
If there is no echo the baby might not necessarily have a hearing problem, but doctors will need to carry out further tests to make sure and to find out why. In the United Kingdom, health authorities say approximately 1 in every 8 tested infants requires further testing, and between 1 and 2 infants in every 1,000 are born with hearing loss in either one or both ears.
What are the treatment options for people with a hearing impairment?
There is help for patients with all types of hearing loss. Treatment depends on why the deafness exists and how severe it is.
Sensorineural hearing loss is incurable. When the hair cells in the cochlea are damaged, they cannot be repaired. However, various treatments and strategies can help improve the patient's quality of life.
Scientists from the University of California, San Francisco, reported in July 2012 that congenital hearing loss can be reversed in a mouse model. They hope their research will eventual lead to gene therapy for humans.
Hearing aids - these are devices that help in hearing. There are several types of hearing aids; they come in a range of sizes, circuitries and levels of power. They do not cure deafness, but amplify the sound that enters the ear so that the listener can hear things more clearly.
Hearing aids consist of a battery, loudspeaker, amplifier and microphone. Today they are very small, discreet and can be fitted inside the ear. Many of the modern ones can distinguish background noise from foreground sounds, such as speech.
For a person with profound deafness, a hearing aid is not suitable.
The audiologist takes an impression of the patient's ear to make sure the device fits well. It will be adjusted to the patients auditory requirements.
Five common types of hearing aids
Examples of hearing aids include:
Behind-the-ear (BTE) hearing aids - these consist of a dome (earmold) and a case, with a connection from one to the other. The case is behind the pinna (outer ear, the part that sticks out); the connection to the dome comes down the front of the ear. The sound from the device is routed to the ear either electrically or acoustically.
BTE hearing aids tend to last longer than other devices because the electrical components are located outside the ear (less moisture and earwax damage). These devices are more popular with children who need a sturdy and easy-to-use device.
In-the-canal (ITC) hearing aids - these fill the outer part of the ear canal and can be seen, but only just. Soft ear inserts, usually made of silicone, are used to position the loudspeaker inside the ear. These devices fit most patients straight away, and have better sound quality.
Completely-in-the canal (CIC) hearing aids - these are tiny devices, but are not recommended for people with severe hearing loss.
Bone conduction hearing aids - for patients with conductive hearing loss, as well as those unable to wear conventional type hearing aids. The vibrating part of the device is held against the mastoid with a headband. The vibrations go through the mastoid bone, to the cochlea. These devices can be painful or uncomfortable if worn for too long.
Cochlear implants - inserted to help patients whose hearing impairment is caused by hair cell damage in the cochlea. The implants usually help most people understand speech better. The latest cochlear implants have new technology which helps patients enjoy music, understand speech better even with background noise about, and use their processors while they are swimming.
The external parts of a left-ear cochlear implant (internal part below)
According to the National Institutes of Health, about 42,600 adults and 28,400 children had cochlear implants in the USA in 2010. The World Health Organization says approximately 219,000 people globally are recipients, most of them in industrial countries. A cochlear implant consists of:
- A microphone that gathers sound from the environment (may be more than one)
- A speech processor which prioritizes sounds that matter more to the patient, such as speech. The electrical sound signals are split into channels and sent through a very thin wire to the transmitter
- A transmitter. This is a coil which is secured with a magnet. It is located behind the outer hear. It transmits the processed sound signals to the internal implanted device
- A surgeon secures a receiver and stimulator in the bone beneath the skin. The signals are converted into electric impulses and sent through internal wires to the electrodes
- Up to 22 electrodes are wound through the cochlea. The impulses are sent to the nerves in the scala tympani, and then directly to the brain. The number of electrodes depends on which company makes the implant.
The internal part of the cochlear implant
Children will usually have cochlear implants in both ears, while adults tend to have one in just one ear.
Sign language and lip-reading
Some people with hearing impairment may have speech problems, as well as difficulties in understanding what other people say. A high percentage of people with hearing impairment can learn other ways of communicating. Lip reading and sign language can replace or complement oral communication.
Lip reading (lipreading) - also known as speechreading is a method for understanding spoken language by watching the speakers lip, facial and tongue movements, as well as extrapolating from the data provided by the context and any residual hearing the patient might have.
People who became hearing impaired after they learnt to speak can pick up lip reading rapidly; this is not the case for those who are born hearing-impaired.
Sign language - this is a language that uses signs made with the hands, facial expressions and body postures, but no sounds - it is used mainly by those who are deaf. There are several different types of sign languages. British sign language is much more different from American sign language than British and American spoken English. British sign language uses a two-handed alphabet, unlike American sign language.
Some countries use the sign language introduced by missionaries from faraway - Norwegian sign language is used in Madagascar.
Sign language is completely different from the spoken form, word order (syntax) and grammar in British sign language is not the same as it is in spoken English. American sign language is more grammatically similar to spoken Japanese than spoken English.
Can hearing impairment be prevented?
There is nothing we can do to prevent congenital deafness (when you are born with the condition), or hearing impairments due to illnesses or accidents. However, some measures can be taken to reduce the risk of losing some of your sense of hearing.
The structures in our ears can be damaged in several different ways. Long term exposure to very loud noise - above 85dB can eventually cause hearing loss. A typical lawn mower emits about 85dB.
The following measures may help protect your hearing:
TV, radio, music players and toys - do not set the volume too high. Children especially are very sensitive to the damaging effects of loud music. Researchers found that noisy toys put children's hearing at risk.
Headphones - focus on isolating what you want to hear; block out all outside noise as much as possible, instead of drowning it out with high volume.
The workplace - if you work in a noisy environment, wear ear plugs or ear muffs. Even in discos, nightclubs, and pubs - ear plugs are discreet and hardly noticeable.
Leisure venues - if you go to pop concerts, motor racing, drag racing and other noisy events, wear ear plugs.
Cotton swabs (UK cotton buds) - do not prod them into your or your children's ears. The same applies for cotton or tissues.