Hearing Loss

Hearing loss - What is hearing loss?

Hearing loss, impairment or deafness may be of two major types:

  • one that develops some time in life
  • one that a baby is born with – or congenital deafness

Most commonly, hearing loss is seen with age or is caused by exposure to loud noises.

How many people does hearing loss affect?

More than 10 million people in the United Kingdom have some form of hearing loss. Of these about 688,000 are severely or profoundly deaf.

Each year nearly 840 babies are born with significant deafness in the UK. Around 1 in a 1000 is deaf at the age of three and nearly 20,000 children aged up to 15 are moderately to profoundly deaf. 1-6

Normal hearing mechanism

The ear consists of a narrow canal or tube that lets in the sound waves. These waves enter the ear canal and strike the ear drum.

The ear drum or the tympanic membrane is a membrane that vibrates as the sound waves hit it. These vibrations are passed to the three small bones (ossicles) inside the middle ear. These are shaped like a tiny hammer, anvil and a stirrup and are called malleus, incus and stapes bones respectively.

The ossicles amplify the vibrations and pass them on to the inner ear. The inner ear contains a shell shaped organ called the cochlea. Within the cochlea are tiny hair cells all along the inner walls. These move in response to the vibrations and send a signal through the auditory nerve to the brain. 

Types of hearing loss

Hearing loss is of two major types. Some people may get conductive hearing loss. This occurs when any of the passages of the sound waves is blocked and the sound waves cannot be transmitted to the ear. The most common causes are:

  • blockage of the ear canal by ear wax
  • perforation of the ear drum
  • build-up of fluid due to an ear infection called glue ear

Another type of hearing loss is sensorineural hearing loss where the auditory nerve and other nerves that carry the information from the sounds heard to the brain are damaged due to age or injury. When people get both types together, the condition is termed mixed type of hearing loss.

Who is affected by hearing loss?

The most common cause of hearing loss is ageing, and three-quarters of people who are deaf are aged over 60. Above the age of 40 more men than women become hard of hearing.

Among those over 80 more women than men are deaf or hard of hearing. This could be because women tend to live longer and there are more of them.

Symptoms and diagnosis of hearing loss

Hearing loss may be mild, moderate, severe or profound. The degree of hearing loss is detected by hearing test called the whisper test. It detects the quietest sound which that person can hear.

The normal hearing range is 0-20 decibels (dB). Around 30 dB are for whispers, 50 dB for average home noises and 60 dB for conversational speech. Sounds like jet engine noises are over 140 dB and are painful.

Hearing loss is measured in decibels hearing loss (dB HL).

  • 25-39 dB HL means mild hearing loss (cannot hear whispers)
  • 40-69 dB HL means moderate (cannot hear conversational speech)
  • 70-94 dB HL is severe (cannot hear shouting)
  • more than 95 dB HL is profound (cannot hear sounds that would be painful for a hearing person)

Some patients have additional symptoms along with hearing loss like tinnitus (buzzing or ringing of the ears), dizziness and fullness of one or both ears.

Diagnosis involves examination of the ear canal for wax, ear drug for perforations etc. An Audiometry is recommended to determine the extent of hearing loss.

Treatment of hearing loss

Type of hearing loss is determinant of the method of therapy. In cases where there is sensorineural damage the patient is recommended:

  • digital hearing aids
  • surgically implanted hearing aids within the middle ear
  • cochlear implants
  • learning a sign language for communication

For those with conductive hearing loss a Bone Anchored Hearing Aid (BAHA) is often suggested. Causes like ear wax can be corrected easily by removal. A perforated ear drum may also be repaired.

Hearing loss due to diseases and age cannot be prevented but reduction of exposure to repeated loud noises can reduce the risk of hearing loss from loud, consistent noise.

Not having music or the television on at a very loud volume and wearing ear protective gear when exposed to noise work environment helps prevents hearing loss.

Types of hearing loss

Hearing loss of hearing impairment may be of two major types - conductive hearing loss and sensorineural hearing loss. A third type is a mixed type that has underlying symptoms of both these types of deafness of hearing loss. 1-6

Normal ear anatomy

The normal ear consists of a narrow canal that lets in the sound waves. This is called the external ear or the ear canal. These waves enter the ear canal and strike the ear drum.

The ear drum (called the tympanic membrane) is a membrane that vibrates as the sound waves hit it. These vibrations are passed to the three small bones (ossicles) inside the middle ear. These are called malleus, incus and stapes bones.

The ossicles move to amplify the vibrations and pass them on to the inner ear. The inner ear contains a shell shaped organ called the cochlea. Within the cochlea are tiny hair cells all along the inner walls. These move in response to the vibrations and send a signal through the auditory nerve to the brain. 

Decibels hearing loss

The normal hearing range is 0-20 decibels (dB). Around 30 dB are for whispers, 50 dB for average home noises and 60 dB for conversational speech. Sounds like jet engine noises are over 140 dB and are painful.

Hearing loss is measured in decibels hearing loss (dB HL).

  • 25-39 dB HL means mild hearing loss (cannot hear whispers)
  • 40-69 dB HL means moderate (cannot hear conversational speech)
  • 70-94 dB HL is severe (cannot hear shouting)
  • more than 95 dB HL is profound (cannot hear sounds that would be painful for a hearing person)

Types of hearing loss

Types of hearing loss include conductive hearing loss, sensorineural hearing loss and mixed type.

Conductive hearing loss

In this the sound waves are unable to pass from the external ear into the inner ear resulting in a hearing loss. The most common reasons are due to:

  • blockage of the ear canal by ear wax
  • perforation of the ear drum
  • build-up of fluid due to an ear infection called glue ear

Sensorineural hearing loss

This occurs where the auditory nerve and other nerves that carry the information from the sounds heard to the brain are damaged due to age or injury.

Hearing loss due to aging is called presbyacusis. After the age of 30 to 40, many people start to lose their hearing in tiny amounts. This increases with age and by 80 many people may have significant hearing impairment.

Presbuacusis occurs when the sensitive hair cells inside the cochlea gradually become damaged or die. The initial symptoms include loss of high-frequency sounds, such as female or children’s voices and difficulty in hearing consonants, making hearing and understanding speech difficult.

Ear injury is another common cause of hearing loss. This occurs due to damage caused by loud noises. The inner structures due to constant exposure to noise become damaged. Exposure to noise causes the hair cells inside the cochlea to be inflamed.

Some drugs may also cause damage to the nerves of the ears leading to sensorineural hearing loss. These include notable antibiotics like aminoglycosides (Gentamicin, Amikacin etc.)

Mixed type of hearing loss

When people get both types together, the condition is termed mixed type of hearing loss.

Causes of hearing loss

Hearing loss is most commonly caused due to two major causes – age related hearing loss and hearing loss due to exposure to loud noises of acoustic trauma. There are numerous other causes that include disease and drugs that may damage the functioning of the ears and lead to hearing loss.

Causes of hearing loss include age related hearing loss, acoustic trauma and so forth. 1-5

Age related hearing loss

This also called presbyacusis and is the largest single cause of hearing impairment. Hearing loss begins normally between ages of 30 and 40. This increases with age until by 80 most people have significant hearing impairment.

Presbyacusis occurs when the sensitive hair cells inside the cochlea gradually become damaged or die.

Common manifestations initially are inability to hear high-frequency sounds, such as female or children’s voices and inability to hear consonants, such as the letters s, t, k, p and f. This makes understanding conversations difficult especially with a background noise.

Hearing loss due to acoustic trauma

Ear damage may be caused due to exposure to loud noises over long periods of time. This repeated exposure to noise causes damage to the delicate inner structure of the ear. The hair cells within the cochlea may be inflamed.

Acoustic trauma and the extent of damage depend on the length of time and the loudness of the noise the person is exposed to. People who work in noisy environment and those who listen to music at a high volume through headphones are at a greater risk.

Hearing loss due to a perforated ear drum

This occurs due to injury or infection of the ear. In children an acute ear infection (acute otitis media) may lead to formation of pus within the middle ear. This may bulge out through the ear drum and the membrane may be perforated. Injury with sharp objects may also cause ear drum to perforate. This leads to a conductive hearing loss.

Hearing loss due to ear wax

Ear wax may get impacted within the ear canal and cause blockage of the ear canal leading to hearing loss. An obstruction of the ear canal with a foreign body like a bead or a small object may also act similarly. This leads to a conductive hearing loss.

Hearing loss due to Otosclerosis

This occurs when there is an abnormal growth of bone in the middle ear. This leads to lack of movement of the ossicles and the sound waves cannot be passed into the inner ear. This leads to a conductive hearing loss.

Genetic hearing loss

Sometimes hearing loss may run in families. This is more commonly of the sensorineural type.

Hearing loss due to viral infections

Viral infections like Mumps, measles and Rubella (German measles) may also cause hearing loss especially in children. This is more commonly of the sensorineural type. Brain infections like meningitis or encephalitis may also cause hearing loss.

Hearing loss due to Meniere’s disease

Meniere’s disease leads to a sensorineural hearing loss along with vertigo and tinnitus or ringing of the ears and feeling of pressure within the ears.

Hearing loss due to acoustic neuroma

A tumor of the auditory nerve that is non-cancerous may also lead to a sensorineural hearing loss.

Other causes of hearing loss

Multiple sclerosis and stroke are other causes of neurological hearing loss.

Head injury may also lead to hearing loss.

Children born with hearing impairments

Children with congenital conditions like Down syndrome, Usher syndrome, Treacher Collins syndrome, Crouzon syndrome, and Alport syndrome may be born with hearing impairment.

Hearing loss as a consequence of some drugs

Some drugs like those used in cancer and antibiotics like Aminoglycoside (gentamicin, Amikacin, Streptomycin etc.) may lead to nerve damage within the ear and hearing loss.

Symptoms and diagnosis of hearing loss

Hearing loss may appear during childhood or later in life or may be present since birth. There are numerous causes of hearing loss and depending on the cause the symptoms vary between individuals.

Hearing loss can gradually develop over time especially if it is age related hearing loss or develop after a short illness if it is related to an acute infection of the middle ear.

Many patients may present with hearing loss along with other symptoms such as dizziness, ringing of the ears or tinnitus and feeling of pressure within the ear(s). 1-5

Symptoms of Congenital hearing impairment

Hearing impairment may be present in some conditions since birth. The symptoms of this condition include:

  • the baby not being startled with a loud noise
  • not turning his or her head to the source of a sound while under four months old
  • not say any word even by the age of one
  • sees the mother but does not respond to her calling him or her
  • seems to hear some sounds but not all sounds

In general, children with delay in learning to talk, unclear speech, talking loudly or asked the speaker to repeat themselves and turning up the volume of the TV so that it is very loud indicates that there may be hearing impairment.

Symptoms of hearing loss

Common complaints include:

  • difficulty in hearing and understanding conversations
  • difficulty in following conversations over the telephone
  • listening to music or television at a volumes higher than other persons
  • missing door bells or phone rings
  • difficulty placing the direction of the oncoming sound

Patients often ask the speaker to repeat and have more difficulty in understanding women and children. They may also have a history of working in a noisy environment.

Symptoms of mild hearing impairment

This means that the patient can hear the quietest sounds between 25 to 39dB. This type of hearing loss means difficulty in understanding whispered speech.

Symptoms of moderate hearing impairment

These persons can hear the quietest sound between 40 to 69dB. A normal conversation becomes difficult for these persons to follow.

Symptoms of severe hearing impairment

The quietest sound that these patients can hear is between 70 to 89dB. These patients cannot hear shouted words and may need sign language for communication.

Symptoms of profound hearing impairment

These patients cannot hear very loud sounds that normally hurt the ears of normal hearing persons.

Other symptoms of hearing loss

Other symptoms include:

  • discharge of clear fluid or pus from the ears
  • pain in the affected ear
  • dizziness
  • tinnitus or ringing of the ear
  • feeling of fullness of the affected ear

Diagnosis of hearing loss

Diagnosis of hearing loss involves ear examination, hearing tests and so forth.

Ear examination

The external ear canal is examined using an otoscope or an auriscope. This helps in detection of a blockage in the ear canal with ear wax or with a foreign object (e.g. a bead), ear canal infection, bulging eardrum indicating an acute middle ear infection, perforation of the ear drum and collection within the ear.

Hearing tests

These are performed using a tuning fork test. A tuning fork is a Y-shaped, metallic object. It is tapped and this releases sound waves at a fixed pitch. The tuning fork is then held close to either ear to detect hearing impairment in the ear.

The physician may also whisper near the ear to detect loss of hearing in the ear. This tests for air conduction of the sound.

Tuning fork tests

A hearing test is followed by further tests called tuning fork tests. Once the tapped tuning fork begins to vibrate, it is held against the bone behind the ear called the mastoid bone.

The sound waves move to the ear and the person hears the sound in the normal ear. This tests for the bone conduction of the sound.

Audiometry test

This is also called Pure Tone Audiometry. Both air and bone conduction can be tested using audiometry. For air conduction, sounds are transmitted to the ear using earphones and the patient is asked to indicate when he or she hears the sound.

Bone conduction is tested to see how well the sound is transmitted through the bone rather than the air. These check for the nerves that transmit sound to the brain as well.