Hearing Loss
Hearing loss affects more than half of adults aged 60 and over in the UK. If untreated, it can have a detrimental impact on your quality of life, emotional and physical well-being, and can even lead to psychological and social problems. More specifically, hearing loss can:
- impair individuals’ ability to hear loved ones;
- reduce clarity when listening to the TV and radio;
- create moments of uncertainty and indecision when following conversation in group situations and background noise;
- pose challenges when trying to judge the distance and direction of sounds such as oncoming traffic when crossing the road;
- lead to experiences of tiredness, fatigue and social withdrawal.
Age-related hearing loss (presbyacusis) develops gradually over many years. This gradual deterioration in hearing can make people inclined to believe that it is others who are ‘mumbling’ and not speaking clearly, rather than it being due to them no longer hearing as well as they once did.
Hearing loss can be described as either: Mild, Moderate, Severe or Profound. The severity of hearing loss you have depends on how loud in decibels (dB) a sound needed to be in order for you to detect it. The severity of hearing loss is likely to be different at different frequencies of sound. You can compare your audiogram (hearing test graph) results to the dB levels associated with the different levels of hearing loss below:
| Normal | Mild | Moderate | Severe | Profound |
|---|---|---|---|---|
| <20 dB HL | 20-40 dB HL | 40-70 dB HL | 70-90 dB HL | >90 dB HL |
If hearing loss has gone unnoticed or left untreated for too long it can lead to ‘auditory deprivation’. Auditory deprivation is when your ears and brain are starved of hearing sounds for a prolonged period of time to the extent they begin to lose their ability to function effectively. It is not known whether the effects of auditory deprivation in adults are permanent or reversible/semi-reversible through late intervention (i.e. wearing of hearing aids).
There are two main types of hearing loss which occur in different regions of the human hearing pathway:
- Conductive hearing loss – due to a blockage or loss of tranmission of sound in the ‘outer’ and/or ‘middle’ ear
- Sensorineural hearing loss – due to permanent damage to the organ of hearing (cochlea) and/or hearing (auditory) nerve located in the ‘inner’ ear
Outer Ear
Sounds are collected by the external part of the ear (pinna) and travel through the ear canal (external auditory meatus). If sounds cannot travel through the outer ear it can cause a conductive hearing loss.
Some outer ear conditions that can cause a conductive hearing loss are:
Cerumen (Ear wax) – this is a yellow/brown substance secreted by the layer of skin lining the external auditory meatus. It serves to lubricate the ear canal preventing it from drying out, reduce the likelihood of fungi and bacterial infections by creating a slightly acidic environment within the ear, capture dead skin cells (keratin) and small foreign bodies (e.g. insects), as well as collecting any dust or dirt roaming the environment. For most people, ear wax naturally migrates out of the ear and so there is no need to clean the ears. However, ear wax can get impacted and trapped in those people who use cotton buds or have narrow ear canals.
Foreign bodies – any object that appears in the ear canal that should not be there is referred to as a foreign body. Examples of foreign bodies are cotton wool, insects and small toys such as marbles (usually placed into the ear canal by children themselves!).
Otitis externa – this is an inflammation of the outer ear skin due to an infection or an eczema type problem. This can cause irritation/itchiness, earache (otalgia) and sometimes even discharge (otorrhea) to weep out of the outer ear.
Exotosis – also known as ‘surfer’s ear’, this is an abnormal growth(s) or lump(s) of the bony portion of the ear canal (near to the eardrum) that can cause it to constrict and narrow. It is caused usually through regular exposure to cold winds and water, hence why it is most prevalent amongst surfer’s.
Stenosis – a gradual narrowing of the external auditory meatus usually as a result of repetitive (chronic) ear canal infections. People with stenosis are more susceptible to developing cholesteotoma.
Cholesteotoma – this is a rare condition caused through the collection of dead skin cells inside your ear. Usually dead skin cells migrate out of the ear but sometimes they can collect inside the ear canal, especially if you have stenosis or an inwards buckled (retracted) eardrum. If left untreated, the cholesteotoma can develop and begin to erode the middle and inner ear structures. It can also grow upwards towards the brain.
Middle Ear
Sounds then arrive at the eardrum (tympanic membrane) causing it to vibrate. The vibrations are transmitted through the three middle ear bones (ossicles). These are known as the ‘malleus’, ‘incus’, and ‘stapes’. If vibrations are not transmitted through the middle ear it can again cause a conductive hearing loss.
Some middle ear conditions that can cause a conductive hearing loss are:
Tympanosclerosis – this is a stiffening, thickening and visible scarring of the eardrum.
Otosclerosis – this is a stiffening of the three middle ear bones due to an abnormal spongy bone growth that normally develops where the stapes connects to the organ of hearing (cochlea).This region is known as the ‘stapes footplate’
Ossicular discontinuity – this is a disconnection (disarticulation) of the three middle ear bones meaning they are loosely or no longer connected together.
Eustachian tube dysfunction – the Eustachian tube is a narrow passage connecting the back of the nose to the air-filled middle ear. Its function is to equalise the air pressure in the middle ear to the air pressure in the atmosphere (i.e. either side of the eardrum). This is because the eardrum is at its most mobile and efficient when the air pressure is equalised on either side. It also allows fluid that builds-up in the middle ear to drain away. Normally, the Eustachian tube is closed and it only opens during moments of yawning, swallowing and chewing. However, if the Eustachian tube becomes blocked and does not open when it should, air in the middle ear gets absorbed to create a ‘vacuum’ and negative middle ear pressure. As a result, the eardrum buckles inwards (retraction).
Middle ear effusion (MEE) – this is a build-up of fluid in the middle ear which normally occurs secondary to Eustachian tube dysfunction because fluid can no longer drain away.
Acute Otitis media – also known as ‘glue ear’, it normally develops from MEE. Over time, the build-up of fluid becomes thick and sticky (viscous) leading to the middle ear becoming infected.
Perforation – this is a hole (rupture) of your eardrum that can be caused through exposure to extremely loud sounds (acoustic trauma), physical damage (physical trauma), extreme and/or sudden atmospheric air pressure changes (barotrauma), middle ear infections (acute otitis media) or surgery (grommets). A small rupture is known as a ‘pin-hole’ perforation and a large/complete rupture is known as a ‘sub-total’ perforation.
Inner Ear
The vibrations transmitted through the middle ear lead to the movement of fluid that fills the organ of hearing (cochlea). As a result, tiny hair cells in the cochlea begin to ‘sway’ generating electrical impulses that travel up the hearing nerve to the brain. The brain recognises these as sound. If there is damage to the inner ear it can cause a permanent sensorineural hearing loss. It is possible to have both a conductive and sensorineural hearing loss. This is known as a mixed hearing loss.
Some inner ear conditions that can cause a sensorineural hearing loss are:
Presbyacusis – this is age-related hearing loss that gradually and progressively deteriorates due to the ageing process. First and foremost, it affects the higher frequencies leading to difficulties hearing speech clearly especially in the presence of background noise. This is because the nerve fibres that code for high frequency sounds are situated near the entrance (apex) of the organ of hearing (cochlea) meaning they are more susceptible to general wear and tear over the years.
Noise exposure – this can either be in response to extremely loud impulse sounds (e.g. firework, gunshot etc.) or an accumulative affect following prolonged exposure to medium to loud sounds over many years (e.g. industrial deafness).
Head trauma – fractures, haemorrhages and tearing of thin membranes in the inner ear (e.g. perilymph fistula) following injuries to the head can cause hearing loss.
Ototoxicity – any drug that can cause hearing loss is referred to as being ‘ototoxic’. Examples of ototoxic drugs are chemotherapy drugs (cisplatin), antibiotics drugs ending in either –micin or –mycin (e.g. gentamicin, erythromycin), diuretics to promote urine production (furesomide), the anti-malarial drug called quinine (also prescribed for leg cramps), and salicylates (including aspirin). Most ototoxic drugs affect the higher frequencies.
Labyrinthitis – this is the spread of infection from the middle ear (and sometimes from infections in the skull/brain lining) to the inner ear structures that can cause vertigo and permanent sensorineural hearing loss.
Meniere’s disease – this is also known as ‘endolymphatic hydrops’. It is believed to be as a direct result of excess inner ear fluid (endolymph) either through over-production (hyperactive endolymphatic sac) or an inability for it to drain out of the inner ear (blocked endolymphatic duct). Excess endolymph causes a swelling in the inner ear which can lead to vertigo, tinnitus, feeling of pressure and hearing loss.
Acoustic Neuroma – this is also known as ‘vestibular schwannoma’. It is a benign tumour that usually develops on the balance nerve that intertwines with the hearing nerve to form the VIII nerve. The tumour can grow and compress against the hearing nerve affecting the electrical signals created by the swaying of hair cells being transmitted to the brain. It is usually accompanied by tinnitus and causes high frequency hearing loss since the nerve fibers that code for high frequency sounds are more exposed.
