What is Hearing Loss?
Hearing loss is common and can affect people of all ages. About 15-20% of adults in the UK have some degree of hearing loss, ranging from mild to severe, with the figure rising to over half of those over the age of 75. Children are also commonly affected, although in this age group the cause is usually due to fluid build up or infection in the middle ear, congenital problems or childhood viral illness rather than an age-related hearing loss more typical in the older age range. Hearing loss can be quite debilitating as it interferes with normal communication with other people in most day to day activities.
How does sound reach the brain?
Sounds first enter the ear canal after being concentrated or funnelled by the outer part of the ear. They then reach and subsequently cause vibrations in the eardrum, which itself results in movements of the three little bones within the middle ear. These are called ossicles, and they bridge the gap between the eardrum and the cochlea (part of the inner ear). The vibrations within the fluid of the cochlea are then translated into electrical signals within the auditory cranial nerve, which transmits these signals directly to the brain stem and auditory nuclei.
Types of deafness
The causes of deafness can be broadly grouped according to which part of the ear is affected by the problem. The objective of hearing is to get the sound waves from the air into the inner ear and auditory nerve. There are therefore two main categories of hearing loss. In the first, sound is prevented from being conducted through the ear canal/eardrum/middle ear ossicles, i.e. it never gets a chance to reach the inner ear. This is called aconductive type deafness. Secondly, the sound may be conducted perfectly adequately through to the inner ear but once it gets there, either the cochlea or auditory nerve fails to transmit the signal efficiently through to the brain. This is known as a sensorineural type hearing loss.
A conductive hearing loss occurs when there is a failure of the conversion of sound waves within the air into movements of the ossicles and subsequently motion of the fluid within the inner ear cochlea. This can occur either because the sound waves are not reaching the eardrum, such as due to wax blocking the ear canal, or because the vibrating mechanisms of the eardrum or ossicles are not working properly, such as because of recurrent or previous infections or scarring.
There are many other causes of conductive hearing loss including a collection of fluid, trauma or fixation of the ossicles in the middle ear (which is called otosclerosis), a build up of skin cells deep in the ear drum (cholesteatoma) or more rarely growths or tumours of the middle or external ears. Fortunately, most of these conditions are readily treated and the hearing loss often reversible, although this is not always the case.
A sensorineural hearing loss is caused by a problem either of the inner ear or of the auditory nerve. By far the most common cause is an age-related hearing loss called presbyacusis. This usually affects both ears to a similar degree, is gradually progressive over many months or years and can be associated with noises in the ear (tinnitus). Other common conditions include inner ear infections (usually viral), trauma, side effects of certain ototoxic medicines (such as gentamicin or high dose aspirin), congenital causes or more rarely a growth or tumour of the auditory nerve. In contrast to conductive problems, the hearing loss associated with a sensorineural abnormality is generally thought to be permanent.
The main difficulty with sensorineural hearing loss is a difficulty in hearing adequately in conversations, especially in the presence of background noise. This is because in a sensorineural hearing loss, it is usually the high pitched sounds which deteriorate preferentially compared with the low pitched sounds. As the human voice is composed principally of relatively high pitched frequencies and background noise of lower pitched sounds, many people find it increasingly difficult to decipher the human voice from the background hubbub. Often people describe the situation that they can hear that something is being said but they cannot easily discriminate what the precise words are.
What are the factors that can make a hearing loss worse?
- Recurrent infections
- Trauma to the ear: This can either be a conductive hearing loss, such as a cotton bud injury directly to the ear drum, or a sensorineural hearing loss such as after a more severe head injury which causes a fracture through the bone of the inner ear
- Ototoxicity: That is, inner ear damage caused by certain medications such as gentamicin
- Barotrauma: In other words, air or water pressure changes such as that experienced whilst flying or scuba diving
- Noise induced damage: This is either a very loud noise for a short duration, such as a bomb blast or clay pigeon shooting, or a not-so-loud noise experienced over many years, such as factory work without ear protection
- Family history of premature hearing loss
When should I get help for my hearing loss?
You should arrange to see your doctor urgently if you have a sudden hearing loss developing over a few hours or days. This is because early treatment of a sudden deafness is associated with better outcomes and should ideally be started with 48-72 hours of onset.
If you think that your hearing loss is mainly or only affecting one ear, you should see your GP, who will probably refer you on to an ENT specialist for further review and possible investigations. There may well be an easily identifiable reason for this but a number of possible diagnoses need to be considered. This is not quite so urgent but nevertheless needs to be addressed.
If you become aware of a more gradual deterioration of your hearing, you should consult your GP in the first instance. He or she will advise as to the most appropriate course of action, which may involve some initial treatment (such as wax drops or antibiotics) and/or initial investigations such as a hearing test. A referral to an ENT specialist may also be necessary.
What is the treatment for hearing loss?
The treatment for a conductive hearing loss very much depends on the precise cause. Wax blocking the ear canal needs to be removed, either with ear drops, syringing or microsuction clearance by a specialist. A hole in the eardrum may need to be repaired surgically (myringoplasty), whilst a cholesteatoma will need to be carefully removed (mastoid surgery). A disruption or fixation of the ossicles can often be repaired and reconstructed.
Whilst there is no absolute cure for a sensorineural hearing loss, the main form of treatment rests with hearing aids which help to amplify or increase the sounds that are transmitted to the inner ear. Unfortunately, background sounds also tend to get louder as well, although hearing aid technology is continually improving and advances are allowing greater degrees of signal to noise discrimination.
What is a hearing aid?
The aim of a hearing aid is to increase the intensity or loudness of the sound reaching the ear. They are made up of three main components: a microphone, an amplifier and a loudspeaker, all powered by a battery.
Hearing aids come in many different shapes, sizes and types, as below:
- Ear level hearing aids
– Behind the ear: The vast majority are of this type
– In the ear: Being smaller does not necessarily mean that it will not be seen as the outer component is still visible. Also it is not suitable for severe deafness owing to the smaller amplifier
– In the canal: These are even smaller than even the in-the-ear ones, so consequently they are only suitable for mild deafness and in patients with reasonable manual dexterity as the buttons and dials are tiny
- Bone conduction hearing aids: These are aids placed directly on the bone behind the ear, held in place by a headband or alice band. They are used in patients with a conductive hearing loss whose ears may be infected or wet and who cannot wear a conventional aid. They can sometimes cause discomfort or sores over the pressure point
- Bone anchored hearing aids (BAHA): Similar to a bone conducting device, only that an operation is performed to secure the hearing aid surgically to the bone behind the ear. Better if a long term option is required or if a bone conducting device does not suit the patient (e.g. in males) or is not well tolerated
- Body worn hearing aids: Suitable for patients with very severe hearing loss where the amplifier within the device is too large to fit into a behind-the-ear aid. Less used nowadays
- CROS aids: These are good for patients with single sided deafness. The microphone is placed on the same side of the head as the deafness, and the sound is routed via a wire round to the good ear, which interprets the sound and thereby allows for better directional sound appreciation and localisation
- Cochlea implants: These are for patients with severe to profound sensorineural hearing loss who gain little or no benefit from conventional aids
How do I choose between an analogue and digital hearing aid?
This discussion is rarely taking place anymore as the majority of hearing aids issued by the NHS and private sectors are part-digital or digital. Digital aids tend to be more selective in filtering out irritating background noise compared with analogue aids, and they can be programmed to preferentially amplify certain sounds, however there is no hearing aid on the market which can perfectly amplify only the key sounds you want to hear.
How can I get a hearing aid?
Most hearing aids are available free of charge through the NHS. Your GP will need to refer you either directly to the hospital’s hearing aid department or to the local ear, nose and throat surgeon.
You can also purchase hearing aids privately. In this case you will have a much wider range of choices and types of aids, although they are quite expensive and do require ongoing maintenance and review to maintain their function. It is worth going to a reputable dealer who offers a trial period in case it is not suitable for you.