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, and
- 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, and
- 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 that 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, and
- 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 - where 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, and
- sensorineural hearing loss - where the sensitive hair cells inside the cochlea, or the auditory nerve, are damaged, either naturally through aging, or as the result of an injury.
Sometimes, both types of hearing loss may be present at the same time. This is known as mixed hearing loss. See the causes section for more information about conductive and sensorineural hearing loss.
Facts
In the UK, hearing impairment is a common condition. The Royal National Institute for Deaf People (RNID) estimates that in the UK there are almost nine million hearing impaired people.
Approximately 28% of people who are hearing impaired are between 16-60 years of age, and 72% are over 60 years of age.
In terms of age-related hearing loss, about 71% of people who are hearing impaired are over 70 years of age. The severity of hearing impairment among this age group is as follows:
- mild - 38%,
- moderate - 52%, and
- severe - 10%.
Approximately 42% of people who are over 50 years of age have some kind of hearing impairment. The severity of hearing impairment among this age group is as follows:
- mild - 52%,
- moderate - 41%, and
- severe - 7%.
In the UK, each year, around 840 babies are born with a significant hearing impairment. About 1 in 1,000 children are deaf at three years of age.
Approximately 20,000 children between 0-15 years of age are moderately to severely deaf, and there are about 12,000 children between this age range who were born deaf.
