Understanding deafness

This is a guide to the ear and how it works, different types of deafness and the hearing tests that are carried out.

Our aim with this page is to give families basic information about deafness. It explains the different types and levels of deafness and includes information on the variety of hearing tests that can be carried out to check a child’s hearing. It explains about the ear and how it works, different types of deafness, the different types of hearing aids, and audiograms.

Students who are doing research about childhood deafness may also find this booklet useful.

We produce a wide range of free publications on childhood deafness. For more information or to order other publications, phone the NDCS Freephone Helpline on 0808 800 8880 or email helpline@ndcs.org.uk.

The ear has two main functions.

    * It receives sound and converts it into signals that the brain can understand.

    * It helps us to balance.

The two functions are closely related.  

The ear is the first part of the hearing system. The pinna (the outside part of the ear) catches sound waves and directs them down the ear canal. The waves then cause the eardrum to vibrate. These vibrations are passed across the middle ear by three tiny bones, the malleus, incus and stapes (sometimes known as the hammer, anvil and stirrup, known together as the ossicles). The bones increase the strength of the vibrations before they pass through the oval window into the cochlea.

The cochlea looks like a snail’s shell. It is filled with fluid and contains thousands of tiny soundsensitive cells. These cells are known as hair cells. The vibrations entering the cochlea cause the fluid and hair cells to move, much like the movement of seaweed on the seabed when waves pass over it.

As the hair cells move, they create a small electrical charge or signal. The auditory nerve carries these signals to the brain where they are understood as sound.

For an ear to work fully and allow us pick up sound, all of these parts must work well. Deafness happens when one or more parts of the system is not working effectively.

There are many reasons why a child can be born deaf or become deaf early in life. It is not always possible to identify the reason, but you may be offered further tests to try and establish the cause of your child’s deafness.

Causes before birth (pre-natal causes)

Around half the deaf children born in the UK every year are deaf because of a genetic (inherited) reason. Deafness can be passed down in families, even though there appears to be no family history of deafness. For about 70% of these deaf children, no other problems will occur. For the other 30%, the gene involved may cause other disabilities or health problems.

Deafness can also be caused by complications during pregnancy. Infections such as rubella, cytomegalovirus (CMV), toxoplasmosis and herpes can cause a child to be born deaf. There are also a range of medicines, known as ototoxic drugs, which can damage a baby’s hearing system before birth.

Causes in early childhood (post-natal causes)

Being born prematurely can increase the risk of a child being deaf or becoming deaf. Premature babies are often more prone to infections that can cause deafness. Severe jaundice or a lack of oxygen at some point can also cause deafness. Infections during early childhood, such as meningitis, measles and mumps, can be responsible for a child becoming deaf.

Occasionally, a head injury or exposure to loud noise can damage the hearing system.

For more information about the tests used to find out the cause of deafness, read our factsheet Why does my child have a hearing loss? (2005) Finding out about my child's deafness
 

Thanks to Contact a Family for letting us reproduce this information from their leaflet Finding Medical Information on the Internet. You can find the full guidelines at  www.judgehealth.org.uk

The internet can be a very useful source of information for families, but the number and types of websites can cause confusion. The aim of this section is to help you decide whether a website provides relevant, good-quality information.

What to look for on support group websites

Support groups’ websites allow you to get in touch with other people.

Consider the following:

• Can you find clear contact details for the organisation that set up the website?
• If there are e-mail lists, bulletin boards and chat rooms, you are likely to be in touch with people who are genuine. But remember, some may have extreme views.
• Check that your personal information will be kept secure and not shared with others.
• See if your personal details are being recorded when you visit the website.
• Can you contact the website manager to report technical problems and provide comments about the site?

The NDCS has an online discussion group called Parent Place, where parents and other family members share information and practical advice.

How reliable is the medical information?

Consider the following:

• Check the author’s name, job title, workplace, and any formal or professional qualifications.
• Check the date the information was put on the site. Medical information can become out of date very quickly.
• Is the information aimed at getting you to buy something?
• Does the information acknowledge that specific conditions affect people in different ways, ranging from mild to severe.
• Check whether the information is based on a person’s own experiences. How the condition affects your child may differ from other people’s experiences.
• Does the information sound extreme?
  

Who is the website for?

Websites are aimed at different groups of people (for example, professionals, academics, members of the public). Detailed pieces of academic research can be confusing, and may not be helpful. Think about who the website is aimed at and how useful the information will be.

Who produced the website?

Websites can be set up by anybody, from respected organisations and experts to people with extreme views and companies trying to sell you something.

Consider the following:

• Look for the name, address and contact details of the organisation. 
• Does the organisation have a registered charity number (if relevant)? What are the aims and purpose of the organisation?
• Check the names and qualifications of any professionals contributing to the website. Is there an Advisory Panel or Review Group?
• Websites should state clearly if the information is based on people’s personal experiences.
• Websites sponsored by commercial organisations may be biased towards certain treatments or products. Adverts that appear on a website might also reflect this.

Websites from outside the UK can be useful, but may refer to medicines using different names from those used here, or ones not licensed for use in this country. There may be different medical practice and treatments in other countries.

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