Page last reviewed: 13/07/2011
Hearing impairment, or deafness, is when your hearing is affected by a disease, disorder or injury.
The structure of the ear
The ear consists of three parts:
- the outer ear
- the middle ear
- the inner ear
The outer ear
The outer ear is made up of a number of parts, including:
- the visible part of the ear on the side of your head (the pinna)
- the ear canals that go into your head
- the eardrum - a thin layer of tissue that separates the outer ear from the middle ear.
The middle ear
The middle ear is located directly behind the eardrum. It is made up of three tiny bones called ossicles, which are also known as the:
- stapes - a stirrup-shaped bone that transmits sound vibrations from the incus to the inner ear
- incus - an anvil-shaped bone that transmits sound vibrations from the malleus to the stapes
- malleus - a hammer-shaped bone that transmits sound vibrations from the eardrum to the incus.
The inner ear
The inner ear is made up of the:
- cochlea - a coiled, spiral tube that contains two fluid-filled chambers
- auditory nerve - the nerve that transmits sounds to the brain.
How does hearing work?
Sound waves enter your ear and make your eardrum vibrate. The vibrations pass on to the three small bones (the ossicles) inside your middle ear. The ossicles amplify (intensify) the vibrations and pass them on to your inner ear.
The cochlea, inside your inner ear, contains many tiny hair cells, which move in response to the vibrations passed from the middle ear. The movement of the hair cells generates an electrical signal that is transmitted to your brain through the auditory nerve.
Types of hearing loss
There are two main types of hearing loss:
- conductive hearing loss - sounds are unable to pass from your outer ear to your inner ear, often as the result of a blockage, such as earwax or a build-up of fluid
- sensorineural hearing loss - the sensitive hair cells inside the cochlea, or the auditory nerve, are damaged, either naturally through ageing, or as the result of an injury.
Sometimes, both types of hearing loss may occur at the same time. This is known as mixed hearing loss. See the Hearing impairment - causes section for more about conductive and sensorineural hearing loss.
Hearing impairment is a common condition. It is estimated that in Ireland 17% of the population have some sort of hearing loss.
Data from the UK indicate that approximately 28% of people who are hearing impaired are between 16-60 years old, and 72% are over 60 years old.
Each year in Ireland, around 100 babies are born with a significant hearing impairment.
Page last reviewed: 13/07/2011
Hearing impairment can be present at birth, or it can develop at a later stage during childhood or adulthood.
The symptoms of hearing impairment will vary depending on what is causing the condition. Some people experience a sudden, profound loss of hearing, perhaps as a result of a viral infection, or an injury to their head or ears. In other cases, a person's hearing will gradually get worse over a long period of time (age-related hearing loss).
Some hearing-related conditions can have symptoms other than hearing loss. For example, tinnitus is a condition where the hearing nerves in the cochlea (the coiled, spiral tube inside the inner ear) become damaged. This can cause symptoms such as:
- continuous or intermittent ringing
- hissing, whistling, roaring or buzzing noises
Levels of hearing impairment
There are four different levels of hearing impairment, which are defined by the quietest sound that you are able to hear, measured in decibels (dB). These are described below.
If you are mildly deaf, the quietest sound that you can hear is between 25-39dB. Mild deafness can sometimes make following speech difficult, particularly in noisy situations.
If you are moderately deaf, the quietest sound that you can hear is between 40-69dB. People with moderate deafness may have difficulty following speech without a hearing aid.
If you are severely deaf, the quietest sound that you are able to hear is between 70-94dB. People with severe deafness will have difficulty listening in background noise, and will rely heavily on the use of hearing aids or a cochlear implant and will usually need to lip-read.
If you are profoundly deaf, the quietest sound that you can hear is 95dB, or more. People with profound deafness usually need to lip-read or use sign language and may benefit from a cochlear implant.
Page last reviewed: 13/07/2011
Age-related hearing loss
Age is the biggest single cause of hearing impairment. Hearing impairment that develops as a result of age is often known as age-related hearing loss, or presbycusis.
Most people begin to lose a small amount of their hearing when they are 30-40 years old. This hearing loss increases as you get older. By age 80, most people will have significant hearing impairment.
Age-related hearing loss occurs when the sensitive hair cells inside the cochlea (the coiled, spiral tube inside the inner ear) gradually become damaged or die.
As your hearing starts to get worse, high-frequency sounds, such as female or children's voices, may become difficult to hear. It may also be harder to hear consonants, such as the letters s, t, k, p and f.
Another common cause of hearing loss is damage to the ear from loud noises. This is known as acoustic trauma, and it can occur when part of the delicate inner structure of the ear becomes damaged. After prolonged exposure to loud noises, the cells inside the spiral part of the cochlea become inflamed.
The loudness of the noise and the length of time that you are exposed to it are important factors in acoustic trauma. If you are exposed to loud noises over a long period of time, you are more likely to develop acoustic trauma. People who are at risk from acoustic trauma include:
- those who work with noisy equipment, such as pneumatic drills or compressed-air hammers
- those who work in environments where there is loud music, such as nightclub staff
- those who listen to music at a high volume through headphones
Conductive hearing loss
Conductive hearing loss occurs when sounds are unable to pass into the inner ear. This is usually due to a blockage in the outer or inner ear, such as having too much ear wax, or from a build-up of fluid caused by conditions such as glue ear, or an ear infection (otitis media).
However, conductive hearing loss can also be caused by:
- a ruptured (burst) eardrum
- otosclerosis - an abnormal growth of bone in the middle ear.
Sensorineural hearing loss
Sensorineural hearing loss occurs following damage to the sensitive hair cells inside the cochlea, or as a result of damage to the auditory nerve. In some cases, both may be damaged.
There are many different causes of sensorineural hearing loss, including:
- age-related hearing loss (presbycusis),
- damage to the inner ear from prolonged exposure to loud noises (acoustic trauma)
- viral infections of the inner ear, such as mumps or measles
- viral infections of the auditory nerve, such as mumps or rubella
- Ménière's disease - a condition that affects a part of the inner ear known as the labyrinth
- acoustic neuroma - a non-cancerous (benign) growth on or near the auditory nerve
- meningitis - an infection of the meninges, which are protective membranes that surround the brain and spinal cord
- encephalitis - inflammation (swelling) of the brain
- multiple sclerosis - a neurological condition that affects the central nervous system (the brain and spinal cord)
Cytotoxic medication, such as that which is used to treat cancer, can damage the cochlea or the auditory nerve, leading to sensorineural hearing loss.
Sometimes, hearing impairment can have both conductive and sensorineural causes.
Page last reviewed: 13/07/2011
Newborn Hearing Screening Programme (NHSP)
It is not easy to identify hearing loss in young babies because they are too young to know that something is wrong. Screening a baby's hearing soon after they are born means that any hearing loss can be identified early.
The HSE Newborn Hearing Screening Programme has started in some areas of the country. After your baby is born, they will be given a number of routine health checks.If your baby is born in Cork, Kerry, Wexford, Waterford or Dublin they will be offered a hearing test soon after birth as part of the new screening programme.
A commonly used test for a baby's hearing is the otoacoustic emissions (OAE) test. If possible, the test will be carried out while your baby is asleep. It involves inserting a tiny probe into the baby's ear.
The probe emits small sounds and checks for a corresponding 'echo' from the ear, which is known as an otoacoustic emission. If there is no response, it does not necessarily mean that your child has a hearing impairment, although further tests will be needed to determine the cause.
Adult hearing tests
Visit your GP if you are having problems with your hearing. A simple way to find out whether you need to seek medical advice is by answering the questions listed below.
- Do you have difficulty hearing over the telephone?
- Do you have difficulty listening when more than one person in the room is talking?
- Do other people complain about the volume of your music or television?
- Do you have to concentrate quite hard to understand the other person when you are having a conversation?
- Do you often miss the sound of the doorbell or the phone ringing?
- Do you often get confused about the direction a sound is coming from?
- Do you regularly have to ask people to repeat themselves?
- Do the voices of women and children seem harder to understand?
- Do you work in a noisy environment?
- Does it seem as though everyone is mumbling?
- Do you often misunderstand what people are saying?
- Can you sometimes hear a hissing, rushing or ringing sound?
- Has someone close to you suggested that you may have a hearing impairment?
If you answer yes to most of these questions, see your GP. They will examine your ear and they may carry out some simple hearing tests.
During an ear examination, an instrument with a light at the end, known as an auriscope (or otoscope), is used to look for anything abnormal, including:
- a discharge - fluid coming out of the ear
- a bulging ear drum - indicating that there is fluid inside the inner ear
- a perforated ear drum - a hole in the eardrum
- a blockage caused by fluid or an object.
Your GP will ask you about your symptoms, including whether you have any pain in your ear, and when you first noticed the hearing loss.
Referral to a specialist
Your GP may refer you to an ear, nose and throat (ENT) specialist, or an audiologist (a hearing specialist). The specialist can carry out further tests to determine what is causing your hearing loss, and they can recommend the best course of treatment.
Some of the hearing tests that you may have include:
- a tuning fork test
- an audiometry test
- a bone oscillator test
These tests are described below.
Tuning fork test
A tuning fork is a Y-shaped, metallic object. When tapped, it produces sound waves at a fixed pitch. It is usually used for tuning instruments. The hearing specialist will tap the tuning fork on their elbow or knee to make it vibrate, then hold it next to your ear. This will indicate whether you can hear sounds that are transmitted through air vibrations.
The specialist conducting the test may also hold the tuning fork against the bone behind your ear (mastoid). This will help them to determine your level of hearing when the sound waves are transmitted to your inner ear through the bone.
During an audiometry test, you will wear earphones that are attached to a machine. Sounds of different tones and volumes will be played through the earphones. You will be asked to indicate whether you have heard them by raising your hand or pressing a button.
The audiologist may also check how well you hear words that are spoken at different volumes. After listening to words that are spoken at different volumes, you will be asked to repeat what you have heard.
Bone oscillator test
The bone oscillator test determines how well you can hear sounds that are transmitted through the bone rather than the air. It is similar to the tuning fork test, but instead of a tuning fork, an instrument called a bone oscillator is placed against the bone behind your ear (mastoid) to determine your level of hearing through the bone.
- Audiometry is any testing that checks hearing.
Page last reviewed: 13/07/2011
The treatment of hearing impairment will depend on the underlying cause of the condition. For people with sensorineural hearing loss, the condition is permanent.
This is because once the sensitive hair cells in the cochlea (the coiled, spiral tube located in the inner ear) are damaged, they cannot be repaired, so they remain damaged for the rest of a person's life.
However, if your hearing is impaired, a number of treatment methods can improve your quality of life. Some of these are described below.
If you have a hearing impairment, you may be able to wear a hearing aid. A hearing aid does not cure a hearing impairment, but it increases the volume of sound entering your ear so that you can hear things more clearly.
A hearing aid is an electronic device that consists of:
- a microphone
- an amplifier
- a loudspeaker
- a battery
Modern hearing aids are very small and discreet, and can be worn inside or behind your ear. The microphone picks up sound, which is made louder by the amplifier. Hearing aids are fitted with devices that can distinguish between background noise, such as traffic, and foreground noise, such as conversation.
Hearing aids are not suitable for everyone. For example, they may not be effective if you have profound hearing impairment. Your GP or audiologist (hearing specialist) will be able to advise you about whether a hearing aid is suitable for you.
If a hearing aid is recommended for you, an audiologist will take an impression of your ear so that the hearing aid will fit you perfectly. The hearing aid will be adjusted to suit your level of hearing impairment. You will also be shown how to use it and care for it. After your hearing aid has been fitted, you will be invited to return for a follow-up appointment in three months time.
Digital Hearing aids
Instead of having moving parts, digital hearing aids contain a very small computer that processes sounds. This enables the hearing aid to be programmed to suit different environments, such as a small quiet room or a large, noisy workshop.
Behind-the-ear (BTE) hearing aids
Behind-the-ear (BTE) hearing aids usually have an earmould which sits inside your ear. The rest of the hearing aid is connected to the earmould and lies behind your outer ear.
Some types of BTE hearing aids have two microphones that enable you to listen to sounds in the general vicinity, or to switch to focus on sounds that are coming from a specific direction. This can be particularly useful in noisy environments.
In-the-ear (ITE) hearing aids
In-the-ear (ITE) hearing aids sit completely inside your ear. The working parts of the hearing aid are either located in a small compartment that is attached to the earmould, or inside the earmould itself.
Completely in-the-canal (CIC) hearing aids
Completely in-the-canal (CIC) hearing aids are even smaller and less visible than ITE hearing aids. However, they may not be recommended if your hearing loss is severe.
Bone conduction hearing aids
Bone conduction hearing aids are recommended for people with conductive hearing loss, or those who cannot wear a more conventional type of hearing aid. Bone conduction hearing aids vibrate in response to the sounds going into the microphone.
The part of the hearing aid that vibrates is held against the bone behind the ear (mastoid) by a headband. The vibrations pass through the mastoid bone to the cochlea, then they are converted into sound in the usual way. Sometimes the ENT surgeon or audiologist will recommend a Bone Anchored Hearing Aid which involves an operation to anchor the bone vibrator into the skull bones
CROS hearing aids are recommended for people who only have hearing in one ear. They work by picking up sounds from the side that does not have hearing, which are then transmitted to the ear that is able to hear.
BiCROS hearing aids work in a similar way to CROS hearing aids and may be useful for people who do not have any hearing in one ear, and have limited hearing in the other ear. The hearing aids also make sounds louder.
Disposable hearing aids
Disposable hearing aids are sometimes recommended for people who have mild to moderate hearing loss. The battery inside a disposable hearing aid usually lasts for about 10 weeks, after which time the hearing aid is thrown away and replaced. Disposable hearing aids cost around £26 a month and are usually only available privately.
Cochlear implants are small hearing devices that are fitted inside your ear during surgery. They have an external sound processor and internal electrodes. The processor converts sound to signals that are then transmitted to the auditory nerve by the electrodes. This means that cochlear implants are only suitable for people whose hearing nerves are functioning normally.
A cochlear implant is sometimes recommended in one ear for children and adults with severe to profound deafness, who do not benefit enough from hearing aids after trying them for three months.
Cochlear implants may also be recommended in both ears for people who have severe to profound deafness in both ears, who do not get enough benefit from hearing aids after trying them for three months. In this case, they may be recommended for:
- adults who are blind or have other disabilities which mean that they depend on hearing sounds for spatial awareness (being aware of your immediate surroundings)
Before a cochlear implant is recommended, you will be assessed to find out whether it will help improve your hearing. During the assessment, any disabilities or communication problems that you have will be taken into consideration, which may mean that the usual hearing tests are not suitable.
If, following your assessment, a cochlear implant or implants are recommended, it/they will be inserted into your ear/s during an operation, and will be switched on a couple of weeks later.
Irish Sign Language (ISL)
Sometimes, hearing impairment can affect your speech as well as your ability to understand other people. Many people with a hearing impairment learn to communicate in other ways instead of, or as well as, using spoken English.
For people who experience hearing loss after they have learnt to talk, lip reading can be a very useful skill. Lip reading is where you watch a person's mouth movements while they are speaking in order to understand what they are saying.
For people who are born with a hearing impairment, lip reading is much more difficult. Those who are born with a hearing impairment often learn a sign language, such as Irish Sign Language (ISL), which is a form of communication that uses hand movements and facial expressions to convey meaning.ISL is completely different from spoken English and has its own grammar and syntax (word order).
Page last reviewed: 13/07/2011
The ears are fragile structures that can be damaged in many ways. It is not always possible to prevent many of the health conditions that affect a person's hearing, but by following the advice below it is possible to reduce your risk of acoustic trauma (hearing loss from loud noise).
- Do not have your television, radio or music on too loud. This is particularly important if you have young children in the house because their ears are more delicate than those of an adult. If you cannot have a comfortable conversation with someone who is two metres away from you (about 6.5ft), turn the volume down.
- Use headphones that block out more outside noise, rather turning up the volume. You can buy add-ons for your existing headphones that block out more outside noise.
- Use ear protection equipment if you work in a noisy environment, such as a pub, nightclub, a garage workshop or on a building site.
- Use ear-protection equipment at loud concerts and at other events where there are high noise levels, such as motor races.
- Do not insert objects into your ears or your children's ears. This includes fingers, cotton buds, cotton wool and tissue.
- Be aware of the symptoms of common causes of hearing loss, such as ear infections (otitis media) and Ménière's disease.
If you or your child are having hearing problems, make an appointment to see your GP as soon as possible.