What is hearing loss?

Hearing loss is the partial or complete loss of hearing in one or both ears. It can occur suddenly in some cases, but typically tends to develop gradually. Hearing loss can be classified as:

  • Slight;
  • Mild;
  • Moderate;
  • Severe, or;
  • Profound.

Sound is measured in units called decibels (dB). Sounds below 75dB are not likely to cause damage that may contribute to hearing loss. However, as the sound increases above 75dB, the risk of it contributing to hearing loss also increases. The risk of developing hearing loss relates to the volume of noise and length of exposure.

The degree of hearing loss can be represented by a hearing loss range in dB. Slight to mild hearing loss in adults can be classified by a loss in the range of 16-40dB. Severe and profound hearing loss in adults may be in the range of 71-91dBs, or more.   

As a general guide, if you need to raise your voice in an environment in order to be heard, then it is potentially noisy enough to cause damage to your hearing. Noise exposure accumulates over a lifetime and every exposure to loud noise contributes to the development of hearing loss.

Hearing loss tends to be more common among the elderly, who may have accumulated damage over their lifetime. It is estimated that up to one in three people over 65 years of age are affected by hearing loss.

As exposure to excessive loud noise can cause hearing loss, the increased usage of loud personal stereo systems may be causing an increased incidence of hearing loss in the younger population.

Some typical examples of noises and their corresponding decibel levels include:

  • Quiet rural area - 30dB;
  • Conversation at home - 50dB;
  • Vacuum cleaner - 70dB;
  • Food blender - 90dB;
  • Jackhammer - 100dB, and;
  • Chainsaw - 120dB.

How does hearing work?

The outer part of the ear collects soundwaves and directs them down the ear canal towards the tympanic membrane, which is also called the eardrum. The eardrum is a thin membrane that is about 10mm wide and located between the ear canal and the middle ear. The eardrum is very sensitive and slight changes in air pressure cause it to move backwards and forwards. Soundwaves cause the eardrum to vibrate.

On the other side of the eardrum is the middle ear. This is made up of a chain of tiny bones, called ossicles, which are connected to the eardrum at one end, and to an opening of the inner ear at the other end. Vibration of the eardrum cause the ossicles to vibrate, which causes movement of fluid within the inner ear.

The cochlea is found within the inner ear and its surface is covered with tiny hairs that help to convert the soundwaves into electrical signals that are sent to the brain, via the auditory nerve. Different sounds cause unique patterns of vibrations of these hairs, sending different electrical signals to the brain.

The anatomy of an ear. 

Cochlea

The spiral-shaped cavity of the inner ear, responsible for converting soundwaves into nerve impulses that the brain recognises as sound.

Ossicles

Three very small bones that form a chain just behind the eardrum, which transmits sound from the outer to the inner ear.

Causes

The ear has three distinct anatomical regions - the outer ear, middle ear and inner ear. Hearing loss caused by damage to the outer or middle ear is classified as conductive hearing loss. Hearing loss caused by damage to the inner ear, the auditory nerve or the area of the brain involved with hearing, is classified as sensorineural hearing loss. When both types occur together, it is referred to as mixed hearing loss.

Outer ear

The outer ear is made up of the external ear and external auditory canal. Hearing loss caused by changes to the outer ear can include earwax or an outer ear infection.

Middle ear

The middle ear is the space between the eardrum and the cochlea. The middle ear contains the ossicles (malleus, incus and stapes). Causes of hearing loss in the middle ear may include a middle ear infection, fluid build-up behind the eardrum, a burst eardrum or stiffening of the ossicles (otosclerosis).

Inner ear

The inner ear is made up of the cochlea and the balance organs. Some changes within the inner ear may be caused by:

  • Aging, which is associated with damage to the hair cells that line the cochlea;
  • Certain medications, which can be toxic to the inner ear or auditory nerve;
  • Meniere's disease, which causes a build-up of excess fluid in the inner ear;
  • Excessive exposure to loud noises;
  • Infections, such as meningitismeasles and mumps, and;
  • Acoustic neuroma, which is a benign tumour of the auditory nerve.

Less common causes of hearing loss include:

  • Interrupted blood supply to the inner parts of the brain, caused by stroke, heart disease and high blood pressure (hypertension), and;
  • Other underlying medical conditions.

Cochlea

The spiral-shaped cavity of the inner ear, responsible for converting soundwaves into nerve impulses that the brain recognises as sound.

External auditory canal

The canal between the outer ear and the eardrum.

Ossicles

Three very small bones that form a chain just behind the eardrum, which transmits sound from the outer to the inner ear.

Risk factors

Risk factors that may increase the likelihood of developing hearing loss may include:

  • Problems during pregnancy, such as a lack of oxygen supply, which lead to the baby developing growth abnormalities;
  • Use of certain toxic medications that can damage the hearing;
  • Ageing;
  • Smoking;
  • Head injury;
  • Recurrent ear infections, and;
  • Repeat exposure to loud noises, such as those that may occur at building sites or nightclubs. 

Signs and symptoms

Symptoms of hearing loss in adults may include:

  • Difficulty following conversations;
  • Asking people to repeat what they say;
  • Difficulty hearing in noisy areas;
  • Having trouble distinguishing between high-pitched sounds, and;
  • Thinking that others seem to mumble.

Depending on the cause, other symptoms may include:

  • Feeling off-balance or dizzy;
  • Ringing or buzzing in the ear, and;
  • A feeling of pressure in the ear.

Signs of hearing loss in a baby include:

  • A lack of response to sudden loud noises;
  • Not turning to face the source of a sound (particularly in babies under four months of age), and;
  • Not speaking single words by the age of one year.

Signs of hearing loss in a child may include:

  • A delay in learning to talk;
  • Turning up the volume of a television until it is very loud;
  • Asking you to repeat what you say, and;
  • Talking loudly.

Methods for diagnosis

Tests used to diagnose hearing loss include:

Physical examination

A detailed physical examination is conducted, giving particular attention to the ear. Your doctor may use an instrument called an otoscope to look into the ear for:

  • Blockage caused by earwax;
  • An ear canal infection;
  • A bulging eardrum, indicative of an infection or fluid in the middle ear, or;
  • A burst eardrum.

The physical exam may include having your individual ears covered one at a time, then asking you to repeat certain words, to assess the level of hearing. A tuning fork may be used, which is a metal instrument that produces a sound when struck. The tuning fork is tapped and held in the air on each side of the head to test the ability to hear vibrations travelling through the air. It is then tapped and placed against the bone behind the ear to test for vibrations travelling through the bone. The differences between vibrations travelling through the air and bone can help your doctor identify if you have conductive or sensorineural hearing loss. 

Audiometry testing

An audiologist (a healthcare professional specialising in hearing and balance disorders) may use an audiometer to formally assess your hearing and identify the severity of hearing loss. During this testing, the audiometer produces different sounds at various frequencies and volumes and you listen to these sounds through headphones and respond when you hear them by pressing a button. There are other hearing tests that can be performed based upon the patients age and language skills. 

Imaging studies

If a tumour or fracture is suspected, the diagnosis may also include imaging such as computerised tomography (CT) scans or magnetic resonance imaging (MRI).

Computerised tomography

A scan that uses X-rays to create a 3D image of the body. This can detect abnormalities more effectively than a simple X-ray can.

Magnetic resonance imaging

A type of imaging that uses a magnetic field and low-energy radio waves, instead of X-rays, to obtain images of organs.

Types of treatment

The treatment for hearing loss will vary widely, depending on its underlying cause and severity. Some of the more typical treatments may include:

  • Antibiotics or antifungal medications for hearing loss caused by an acute infection;
  • Surgery to repair the damaged ear structures and restore the hearing if trauma has caused the hearing loss;  
  • Surgery for chronic ear infections, chronic middle ear fluid or a tumour;
  • A cochlear implant to improve the level of hearing in some people with some type of sensorineural hearing loss. It is a small electrical device that is placed under the skin behind the ear that translates sound vibrations into electrical signals, which can then be interpreted by the brain as meaningful sounds;
  • Corticosteroids, which act to reduce the inflammation in the inner ear structures;
  • Wax softeners or flushing the ear with warm water to gently soften and remove excess build-up, and;
  • A low-sodium diet, diuretics and corticosteroids for Meniere's disease.

Some other devices or systems that may also prove beneficial for people with hearing loss include:

  • Using sign language;
  • Hearing aids,
  • Aids, such as alert systems for doorbells, smoke detectors, and alarms that send visual cues or vibrations;
  • Telephone amplifying devices to make it easier to talk on a phone, and;
  • Television and radio listening systems to make it easier to listen without being disturbed by background noise.

When talking with someone with hearing loss, it may be helpful to:

  • Face the person and stand close to them;
  • Slow the rate of speech;
  • Be patient;
  • Try to make sure only one person talks at a time, and;
  • Include hand and body gestures to aid communication.

Diuretics

A substance that promotes the production and excretion of urine.

Potential complications

Hearing loss can significantly affect quality of life. Complications may vary depending on the cause and severity of the hearing loss, but some common problems include:

  • Decreased academic performance in children;
  • Anxiety;
  • Depression;
  • A sense of isolation, and;
  • Difficulty finding and maintaining ongoing employment.

Prognosis

Most cases of hearing loss show improvement once the underlying cause is identified and treated. However, since the most common cause is ageing, hearing loss can often be a progressive condition. In some people, effective devices and aids can offer a much improved quality of life.

Prevention

Hearing loss prevention includes:

  • Avoiding or reducing exposure to loud noises;
  • Maintaining good ear hygiene;
  • Following local immunisation guidelines for childhood illnesses;
  • Screening and treatment of conditions early in pregnancy;
  • Seeking medical advice early for ear infections, and;
  • Early assessment for babies at high risk, such as those with meningitis.