Hearing

Causes of hearing loss

There are two types of hearing problem - 'conductive', when sound is not able to pass through the outer or middle ear, and 'sensorineural', when the inner chamber of the ear (cochlea) or the auditory nerve that transmits the sound signals to the brain are affected.

The sensorineural kind of hearing loss becomes more common as we get older, usually due to a condition called presbyacusis.

Conductive hearing problems can include:

• middle ear infections
• collection of fluid in the middle ear (known as "glue ear" in children)
• blockage of the outer ear by wax
• damage to the eardrum by infection or an injury
• otosclerosis, a condition in which the tiny bones of the middle ear (the ossicles) which normally move to transmit sound become immobile
• arthritis can also affect the movement of the ossicles.

Sensorineural hearing problems can include:

• age-related hearing loss – known as presbyacusis
• injury to the inner ear caused by loud noise (acoustic trauma)
• infections caused by viruses – these can include mumps, measles or rubella (German measles)
• abnormal pressure in the inner ear – known as Ménière's disease
• the effects of certain antibiotics and also aspirin and quinine, which can affect the hair cells
• non-cancerous growths that affect the auditory nerve

Presbyacusis

Presbyacusis tends to develop from around the age of 40. It progresses gradually and affects both ears equally, although you may not notice it for quite a few years.
The first symptom is problems hearing the high frequency sounds 'sh', 'k', 'p' and 'f' in everyday speech. Children and women's voices tend to be higher pitched and so they may be the ones that initially become more difficult to understand. As presbyacusis progresses it is harder to tell the difference between similar sounds.

Noises in the ears known as tinnitus can be linked to presbyacusis

What causes it?

Miniscule hair cells line the spiral walls of the cochlea. Sound waves travel through the outer sections of the ear to the cochlea, and the hair cells bend when they hit them. This movement produces chemical signals, which are sent via a nerve straight to the brain. The brain interprets the chemical signals as sounds and that is how we hear.

Presbyacusis is caused by the loss of these tiny hair cells from the inner chamber of the ear. We have about 16,000 hair cells in each cochlea, and they play a vital part of the chain of events that enables us to hear.

Unfortunately, we tend to lose about 40 per cent of them by the time we are 65. We cannot regenerate them once they are damaged.

Will everyone get it?

Most of us will lose some of our hearing as we get older because of presbyacusis. The main cause is wear and tear to delicate hair cells over time, but the following factors can play a part:

• regular exposure to loud noise
• history of middle ear disease
• if other people in your family have presbyacusis
• a high-fat diet – impairs the blood flow to your ears

Checklist of common hearing loss symptoms

• People seem to mumble or speak unclearly and you have difficulty understanding them – particularly when there is background noise.
• It is hard to hear people on the telephone.
• You're the only one in a group who is having difficulty keeping up with the conversation.
• Other people think that you play music too loudly or turn the TV up too high.
• You find conversations tiring because you have to concentrate hard on what people are saying.

For more information about hearing loss visit:
www.actiononhearingloss.org.uk