Cairns Audiology Group - Hearing - Technology - Communication - Solutions

CALL (07) 4054 5561

OR

FAX (07) 3036 6928

Hearing Loss

 

  • How Hearing Works (Link to How Hearing Works Section Below)
  • What Causes Hearing Loss (Link to What Causes Hearing Loss subheading below)
  • Type of Hearing Loss (Link to Type of hearing loss subheading below)
  • Degree of Hearing Loss (Link to Degree of hearing loss subheading below)
  • Configuration of Hearing Loss (Link to Configuration of hearing loss subheading below)
  • Hearing Loss in Children (Link to hearing loss in Children subheading below)


How Hearing works:
Hearing is one of the five senses. It is a complex process of detecting sound and attaching meaning to it. The ability to hear is critical to understanding the world around us.

The human ear is fully developed at birth and can respond to sounds that are very faint as well as sounds that are very loud.

The ear can be divided into three parts leading up to the brain – the outer ear, middle ear and the inner ear.

  • The outer ear consists of the pinna and the ear canal. The pinna – the part of the "ear" that we see on each side of our head, serves as a collector of sound vibrations around us and guides the vibrations into the ear canal. The lumps and ridges in the pinna help us decide the direction and source of sound.
  • The middle ear begins with the eardrum at the end of the ear canal and also includes the air filled space behind the ear drum. The middle ear space contains three tiny bones, called the ossicles. These three bones form a connection from the eardrum to the inner ear. As sound waves hit the eardrum, the eardrum moves back and forth causing the ossicles to also move. As a result, the sound wave is changed to a mechanical vibration.
  • The inner ear contains the sensory organs for hearing (the cochlea) and balance (the semi-circular canals). The cochlea is a bony structure that is filled with fluid and contains sensory hair hells, the nerve receptors for hearing. The mechanical vibration passed on from the middle ear system moved a membrane in the cochlea known as the oval widow which in turn passes the vibration on to the fluid within the cochlea. The vibration of the fluid then bends and stimulates the sensory hair cells. The hair cells then change the vibration of the fluid into nerve impulses which are then passed up the hearing nerve to the auditory cortex in the brain.


What causes hearing loss?
Hearing loss is caused by damage to any of the parts of the ear above or by interruption to the pathway of sound through the auditory system. Congenital or hereditary hearing loss is present at birth or soon after. Acquired hearing loss is developed later in life resulting from injury, trauma or illness. When describing hearing loss, we look at three factors, the type of hearing loss, the degree of hearing loss and the configuration of the hearing loss.

Type of Hearing Loss:
Hearing loss can be categorized by which part of the auditory system is damaged. There are three basic types of hearing loss;

•    Conductive Hearing Loss
Conductive hearing loss results from some disruption of the outer or middle ear system and can occur for a number or reasons including;

  • Cerumen (wax) build up in the ear canal
  • Foreign body in the ear canal
  • Perforation of the tympanic membrane (ear drum)
  • Damage to the bones in the middle ear by trauma or disease (otosclerosis).
  • Effusion in the middle ear space (glue ear)
  • Absence or malformation of the outer ear, ear canal, or middle ear


Conductive hearing loss can often be managed medically and requires review by a GP and/or ENT Specialist.

•    Sensorineural Hearing Loss
Sensorineural hearing loss results from damage to the inner ear or neural auditory pathways and can occur for a number of reasons including;

  • Genetic factors such as a family history of hearing loss or associated syndrome
  • Ageing
  • Trauma such as head injury or acoustic shock
  • Illness such as measles or meningitis
  • Ototoxic damage such as certain medications and chemicals
  • Prolonged noise exposure


Once damage has occurred to the inner ear or neural auditory pathway, it is usually permanent and cannot be treated medically, with one of the main management options being the use of hearing aids or assistive listening devices.

•    Mixed Hearing Loss
Sometimes a conductive hearing loss occurs in combination with a sensorineural hearing loss. In other words, there may be damage in the outer or middle ear and in the inner ear (cochlea) or auditory nerve. When this occurs, the hearing loss is referred to as a mixed hearing loss.

Degrees of hearing loss:
After your hearing assessment your Audiologist will be able to accurately determine the degree of hearing loss. The severity of your hearing loss is measured in terms of its functional impact on your quality of life.

•    Mild: 21–45 dB
Difficulty hearing soft speech but able to hear conversations in quiet situations.

•    Moderate: 46–65 dB
Difficulty hearing normal conversational speech especially in the presence of background noise.

•    Severe: 66–90 dB
Normal conversational speech is inaudible and you will rely heavily on facial cues and lip reading.

•    Profound: 91 dB +
Normal conversational speech is inaudible and you will rely heavily on facial cues and lip reading. There is a big variation in the success of these clients with hearing aid fitting.  

Configuration of Hearing Loss:
The configuration, or shape, of the hearing loss refers to the degree and pattern of hearing loss across the frequency range. For example, a hearing loss that only affects the high frequencies would be described as a high-frequency loss.

Other descriptors associated with the configuration of the hearing loss are;

•    Bilateral versus unilateral
Bilateral means hearing loss in both ears. Unilateral means hearing loss in one ear.
•    Symmetrical versus asymmetrical
Symmetrical means the hearing loss is the same in each ear. Asymmetrical means the hearing loss is different in each ear.
•    Progressive versus sudden hearing loss
Progressive means that hearing loss becomes worse gradually over time. Sudden means hearing loss that happens quickly.
•    Fluctuating versus stable hearing loss
Fluctuating means hearing loss that changes over time—sometimes getting better, sometimes getting worse.

Hearing Loss in Children:
Research has shown that adequate hearing in the first 6 months is essential to develop normal speech and language skills. In Queensland all babies are offered a neonatal hearing screen at birth and those who do not pass or who are at risk of hearing loss (e.g. those with a family history of hearing loss) are referred on for additional testing and monitoring. However, there are certain situations where a hearing loss may develop after the neonatal hearing screen so it’s important for families to be aware if their child is meeting listening milestones especially if they have a history of illness, trauma or infection.

Sound in the environment will elicit different responses from a baby depending on how alert they are at the time. Babies may react to soft sounds when they are in a pre-sleep state, but may show no significant response when they are awake and playing. Babies will also respond to voices, especially familiar voices, at a softer level than other environmental sounds and they also may lose interest in particular sounds and not continue to respond to sounds that are repetitive.

If you are concerned about your child’s hearing or speech and language development speak to your GP or contact Cairns Audiology Group on 07 4054 5561 for an appointment.

Listening Milestones for Babies:

From birth to 4 weeks of age babies will;

  • Respond best to closer sounds
  • Be startled by loud noises
  • Widen their eyes, blink or increase suckling in response to sudden loud sounds
  • Wake from sleep in response to sounds
  • Look towards familiar or continuous sounds


From 1 to 4 months babies will;

  • Widen or blink eyes in response to sounds
  • Shift eyes towards sounds
  • Begin turning towards sounds


From 4 to 7 months babies will;

  • Turn consistently towards sounds
  • Become settled in response to familiar comforting sounds
  • Appears to listen and may mimic some basic sounds