Sound enters the ear canal as a pressure wave of varying frequency (pitch) and amplitude (volume). These pressure waves pass down the ear canal and beat upon the eardrum causing the eardrum to vibrate. The ear canal (up to the ear drum) and the Pinna (the ear itself) form the 'outer ear'.

The eardrum connects to 3 small ossicles (bones) know as the Malleus (the hammer), the Incus (the anvil) and the Stapes (the stirrup - the smallest bone in the human body!). The Malleus is connected to the eardrum and links to the Stapes via the Incus. The stapes is attached to a small oval window at the entrance to the cochlea (the nerve centre or 'inner ear'). The beating eardrum sends sympathetic vibrations through the middle ear bones into the cochlea. The eardrum and the 3 bones form the 'middle ear'.

The cochlea is a tiny cavity (4mm long) formed within the cranium shaped like a snail shell, filled with a thick fluid and lined inside with thousands of microscopic hair cells / nerve endings. The travelling wave stimulates specific hair cells along the cochlea according to the exact frequency and amplitude of the continuous stream of sound signals, and triggers an electrical impulse that is sent to the brain via the auditory cortex.

We thus perceive sound as electrical impulses!

Damage or obstruction to any of the components between the outer ear and the auditory cortex can therefore cause a hearing loss.


What are the different types of hearing loss?

Presbyacusis (hearing associated with advancing age)

The most common general form of hearing loss resulting in a slow progressive deterioration of the hearing. Although there are varying types of pathology that can result in presbyacusis, the most common cause is hair cell degeneration within the cochlea leading to less electrical impulse signals being sent to the brain. This degeneration is commonly caused by noise exposure, but can also be bought on by vascular, dietary and stress related problems amongst others.

Presbyacusis is permanent and can only be treated with hearing aids.

Being a slow progressive deterioration, presbyacusis normally takes a few years before a person will recognise or even admit they have a problem. A classic indication of someone suffering from presbyacusis is that they will often complain that people mumble. Why???

Speech can be split into low and high frequency. The low frequency content is made up of the vowels, deeper resonating elements that give off volume, and the high frequency content is made up of the consonants, the quieter T's, and S's etc that start and end words, and defines clarity. As presbyacusis has more impact on the higher frequencies a sufferer may hear the volume of speech (the vowel content) but will inevitably miss the clarity (the consonant content). Thus a sufferer will generally cope much better 1 to 1 where the brain can fill in the gaps they are missing, than when background noise is present and the brain cannot fill in the gaps so readily, or between rooms where lip reading is not possible. Background noise is generally low frequency.

Digital hearing aids were developed for this type of loss and have now reached such a level so as to restore a much better quality of life for most sufferers, even in noisy environments.

Noise induced hearing loss

Noise induced hearing loss can be caused by long duration exposure (such as factory machinery) or sudden high intensity exposure (such as bomb damage or gun fire).

The resulting damage is the same as for presbyacusis but may result in slightly different test results. Sudden high intensity exposure can often cause severe high frequency damage whilst very minimal low frequency damage. This means that such a sufferer may hear low frequency volume of speech just as ably as a teenager, but may miss the high frequency clarity completely. As such, these sufferers can be in denial for longer periods and are less partial to wearing aids, as they hear many sounds loud enough.

Open-fit (OTE) hearing aids have been developed to overcome this type of loss, restoring clarity, whilst providing a comfortable, discreet solution.

Perforated Eardrums

May result from violent changes in pressure (a slap or explosion etc), direct trauma (from a cotton bud, hairclip etc), excessive pressure build up within the middle ear (from blocked Eustachian tubes), and very rarely from careless syringing.

Patients suffering from perforated eardrums should seek medical attention prior to being fitted with hearing aids as some perforations can heal spontaneously. Permanent perforations can normally be easily treated with modern hearing aids, but wearers should give extra attention to cleaning and maintenance of the hearing aids so as to avoid infection setting in. Some doctors may advise against the use of aids for this reason.

Otosclerosis

A growth of extra spongy-type bone that forms on the middle ear bones that gradually hardens preventing transmission of the sound signal to pass from the stapes bone to the cochlea.

This is a hereditary disease affecting 1 in 200 of the population, with the onset occurring usually between the ages of 20 and 30 years.

Patients with otosclerosis should seek medical assistance as surgery may be offered to cure the problem, normally in the form of a stapedectomy.

Surgery is the treatment of choice but eventually the bony outgrowth may form back. There are contra-indications to surgery for some clients, and it should be noted that surgery is not always successful, which can in the worst cases lead to complete deafness. See www.stapedectomy.co.uk for more information.

Hearing aids are usually very successful in overcoming this type of hearing loss.

Infections and Ototoxic drugs

Infections and drugs within the bloodstream can cause damage to the inner ear. These normally result in more rapid and severe losses and can also be congenital, being passed from mother to unborn child. These losses can often be successfully treated with hearing aids.

Many more causes of loss can occur and our dispensers will be happy to discuss any concerns you may have.