When hearing goes wrong
"I am imagination. I can see what the eyes cannot see. I can hear what the ears cannot hear. I can feel what the heart cannot feel." Peter Nivio Zarlenga
Often deafness and hearing loss are described using words like ‘normal’, ‘mild’, ‘moderate’, ‘severe’, and ‘profound’. These are terms used by doctors and other medical professionals such as audiologists who are medically qualified people who specialise in the ears and hearing – but what do they mean?
Deafness and hearing loss are measured in units called dBHL – dB stands for decibels and HL stands for ‘hearing level’.
A hearing test finds the quietest sounds a person can hear – their thresholds – across a range of frequencies (pitches of sounds). The higher the threshold level, i.e. the louder a sound has to be before the person can hear it, in dBHL, the greater the hearing loss. High frequency hearing loss means hearing is poorest for high pitched sounds. Low frequency hearing loss means hearing is poorest for low pitch sounds. A flat hearing loss means a similar hearing loss across all frequencies.
Normal hearing
Someone with thresholds between 0 and 20 dBHL across all the frequencies is said to have ‘normal’ hearing.
Mild hearing loss
The quietest sounds people with mild deafness can hear is between 21 and 39dBHL. They may have difficulty following speech in noisy situations.
Moderate hearing loss
The quietest sounds people with moderate deafness can hear is between 40 and 69 dBHL. People with moderate deafness will have difficulty following speech without a hearing aid.
Severe hearing loss
The quietest sounds people with severe deafness can hear is between 70 and 94 dBHL. They rely on lip reading a lot, even with a hearing aid. They often use British Sign Language (BSL) as their preferred way to communicate.
Profound hearing loss
The quietest sounds profoundly deaf people can hear is 95dBHL. BSL is often their first language, especially those born deaf or who lost their hearing at an early age. Severely or profoundly deaf adults, those who have lost their hearing later in life tend not to use BSL so much, and often rely on lip reading.
Ear problems and causes of deafness
Hearing is a complex process and it isn't always known precisely what causes deafness in an individual, however, often through hearing and other tests, doctors can work out the cause of the hearing loss. Once hearing is lost, however, there is usually little that can be done to restore it.
Blockages in the ear canal may affect the hearing, and are usually caused by wax, which is the body's way of keeping the ears clean. Wax usually comes out of the ear on its own, but if it gets too hard it may need to be removed by a doctor or a nurse. Cotton buds etc. should not be used to try and get wax out of the ears as they can push the wax onto the eardrum, which can cause infection, pain and deafness. Once the wax is removed hearing will return to normal.
Otitis externa is where the skin of the ear canal becomes inflamed, for example if you have scratched your ear or you have eczema. It may be painful and give you a watery discharge from your ears but it doesn't usually cause hearing loss. Ear drops from your doctor may help.
Otitis media is an infection or inflammation of the middle ear caused by a viral or bacterial infection. This can cause the Eustachian tube to become blocked, preventing air from reaching the middle ear and the middle ear fills up with fluid that becomes thick, like glue, and is known as glue ear. This causes reduced movement of the eardrum and ossicles and reduces hearing. The changes in pressure due to the Eustachian tubes being blocked can cause pain. Children are more likely than adults to get glue ear. In most cases it gets better without treatment and hearing returns to normal. If it doesn't get better on its own an operation called a myringotomy where a tiny ventilation tube called a grommet is inserted temporarily into the eardrum.
Otosclerosis runs in families and often begins around the age of 30. It tends to affect more women than men. Otosclerosis is caused by a bony overgrowth of the stapes, one of the chain of ossicles in the middle ear. This link in the chain becomes more rigid and sound vibrations can't pass through it and hearing will gradually become worse. Hearing aids can be useful for people with otosclerosis unless hearing loss is severe. Often, an operation called a stapesectomy can be performed, where a tiny ‘peg’ replaces the stapes.
Damaged ossicles can be caused by serious infections and head injuries. Sometimes malformed ossicles are present from birth. They can be repaired or replaced by an operation called an ossiculoplasty.
Perforated eardrums can be caused by untreated otitis media and other infections, head injuries, explosions, or poking things in your ear. Normally they heal naturally and any hearing loss is temporary. If the damage is more serious and operation called a myringoplasty can be performed, where a tissue graft is used to patch the hole.
These types of problems, which sometimes can affect hearing all happen in the outer or middle ear and cause problems with the conduction of sound to the inner ear, so this type of hearing loss is called conductive hearing loss. Hearing loss that is caused by problems in the inner ear is called sensorineural hearing loss.
Sensorineural hearing loss
Hearing loss which is caused by factors within the inner ear is called sensorineural hearing loss. This word though actually describes two types of hearing loss, sensory hearing loss, and neural hearing loss. Sensory hearing loss is due to problems in the cochlea, whereas neural hearing loss involves the auditory (8th cranial) nerve. It may be difficult to differentiate between sensory and neural hearing loss, but specialised hearing tests can pinpoint the difference.
Sensorineural hearing loss is often the result of damage to the tiny hair cells in the cochlea. Unlike with disorders that affect the outer and middle ear, in which hearing loss is usually temporary and treated, sensorineural hearing loss due to damage to the hairs in the cochlea is permanent as the hair cells can't be replaced.
There are many causes of sensorineural hearing loss. Some people have conductive and sensorineural hearing loss, mixed hearing loss. Some of these are explored below.
Some of the causes of sensorineural hearing loss are:
Disease
Some illnesses and diseases can cause damage to the inner ear, including mumps or meningitis and some neurological conditions. Though quite rare, tumours on the 8th cranial (auditory) nerve can also cause deafness. Specialised hearing tests and investigations may be needed to find the cause of sensorineural hearing loss.
Drugs
Some strong drugs have side effects that affect the hairs of the cochlea. These are called ototoxic drugs. In particular, platinum–based chemotherapy drugs and antibiotics called aminoglycosides, such as streptomycin and gentamicin can damage hearing. Many drugs have ototoxic side effects if taken in high doses or for prolonged periods of time. Sometimes the ototoxic effects are temporary and hearing may improve when you stop taking the drug. With others, hearing loss may be permanent. If you are prescribed drugs which are ototoxic, your doctor should warn you about the potential side effects and risks, and there may be alternative drugs you could take instead.
Noise
Noise induced hearing loss is caused by exposure to excessive or loud noise. Exposure to loud noise can cause temporary or permanent hearing loss. Hearing loss is likely to become permanent if exposure to noise is prolonged or repeated.
Temporary threshold shift is a temporary hearing loss which is usually a temporary dullness in hearing after you've been exposed to loud noise. Hearing usually returns to normal within 48 hours, but this varies on the loudness of the noise, and how long you were exposed to it.
Permanent threshold shift is when hearing doesn't return to normal within 48 hours. This type of permanent hearing loss can be due to noise, or acoustic trauma.
Noise induced hearing loss happens when you have been exposed to loud noise over a long period of time, and is usually worst in the high frequencies. Speech sounds with the highest frequencies are consonant sounds such as "s", "sh", "t" and "p". The hearing loss will be similar in both ears and will get worse if you continue to be exposed to loud noise. The effect on hearing may not be noticed until years after you were exposed to the noise.
Acoustic trauma occurs when you are exposed to a very loud noise for a short period of time, for example, if you're close to an explosion or gunfire. This can cause a sudden hearing loss that is worst in the ear closest to the sound. It is usually a sensorineural hearing loss, though in some cases a very intense sound can perforate your eardrum.
What types of noise can cause noise induced hearing loss?
Any loud noise can cause temporary or permanent hearing loss. Some of the situations where exposure to loud noise can cause hearing loss can include:
- working with or near to loud machinery or other equipment (though employers have a legal duty to protect their employees from damaging levels of noise)
- working with or pursuing leisure activities involving explosives or guns
- musicians and those who regularly attend concerts
- working in or regularly going to pubs, bars and nightclubs with very loud music
- listening to music at a high volume through headphones
Head injury
A serious head injury with a skull fracture can sometimes cause hearing loss.
Anti natal factors
Sometimes deafness can be congenital (present from birth). Deafness can run in families and is thought to have a genetic cause. Although doctors know about more than 50 genes for hearing, only a few are routinely tested for as many genes are too large to be tested, or they cause deafness in only a few people and accurate testing has not been developed for these genes. Where deafness is due to a genetic cause it is thought that genes that produce proteins that are essential for hearing are faulty. In some cases the genes which are faulty are passed down the mitochondrial DNA. Most of our genes are located on chromosomes, but some are found in structures called mitochondria in the cells of our bodies. Mitochondrial are only inherited from our mothers. This means that if deafness is caused by a mutation in a mitochondrial gene, only women can pass on deafness to their children, though both men and women can have this type of deafness. Congenital deafness can also be caused by factors during pregnancy, for example a mother contracting German Measles (rubella), which can cause deafness in the unborn child, or to a baby following a premature birth or difficult labour.
Ageing
Deafness is often a result of natural ageing. Over 50% of people over 60 have some degree of hearing loss. This is a condition called presbyacusis. Presbyacusis is due to the loss of specialised cells that are needed for the cochlea to work properly. This is a natural process, and while nothing can be done to reverse the effects of presbyacusis, hearing aids and other equipment can help people with a hearing loss in their daily lives.
Our articles Do I have a hearing loss? and Coping with hearing loss look at signs of hearing loss and the equipment and support that is available to people with a hearing loss to help them in their daily lives.
(Adapted from material from the RNID – www.rnid.org.uk↗)
