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 on the HSE website for more about conductive and sensorineural hearing loss.

Facts

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.