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About hearing loss

Endbulbs of Held showing hearing loss, deep inside mouse cochlea.
Endbulbs of Held showing hearing loss, deep inside mouse cochlea.

The cochlea is an extremely delicate structure. Disease, head trauma, ageing, drugs, and loud noise can cause its fine sensory hair cells to die. As they die, our hearing diminishes — but the damage is permanent.

Although only 0.1-0.2% of Australian children are born deaf, it is estimated that 20% of Australian adults suffer from significant hearing loss. The number of affected Australians increases to 50% over 65 and to 75% of people over 70 years of age. As life expectancy continues to rise, the majority of us will face the final decade of our lives with a significant communication disorder.

For reasons we can’t explain, ageing typically causes the hair cells corresponding to high frequencies to die first. This might be noticed when consonant sounds like ‘s’, ‘f’ and ‘th’ become difficult to distinguish.

Hearing loss has many adverse symptoms:

  • speech comprehension in a noisy background is lost
  • tinnitus or ringing of the ears often emerges
  • and sometimes there’s severe loudness distortion.

As hearing loss increases, sounds can be heard, but the details are indistinct, especially in noisy backgrounds. Hearing loss is not just about volume – amplifying a fuzzy signal just gives you a loud fuzzy signal. Meaningful hearing requires our perception of details of the sounds.

Most importantly, when the brain no longer receives adequate stimulation, it rewires itself. Some of the parts previously dedicated to hearing are used for other functions. And just as amputees suffer phantom limb pain, hearing loss can give rise to phantom sounds, like tinnitus.

In children, hearing loss impairs speech and language development, which in turn undermines academic achievement. In adults, it has a negative impact on employment opportunities and social functioning. It can cause social isolation that develops into depression and early onset dementia.

  • Risks
  • Symptoms
  • Diagnosis & Treatment

The main risk factors are noise, disease, drugs, chemicals and head trauma. Noise is like sunlight or radiation: a little is OK but a lot is damaging. Cancer drugs and some antibiotics are especially dangerous to hearing. The most common cause of hearing loss is a result of exposure to loud sounds — gun shots, motorcycles, power tools, concerts and clubs, personal listening devices and hair dryers.

Because of the relatively long delay between noise exposure and hearing loss, it is difficult to notice the consequences of damage. Moreover, the brain is good at guessing and using ‘context’ cues such as subject matter, body language, lip reading and logic to make sense of speech.

Hearing loss falls into two broad categories:

  • Conductive hearing loss — caused by damage or a blockage to the outer and/or middle ear and can be acquired or congenital. Loss of loudness is the key symptom. Causes may include perforated eardrums, middle ear infections (‘glue ear’), blockage of the ear canal by impacted wax, infection, or foreign objects, and otosclerosis (a hereditary condition where bone grows around one of the bones of the middle ear).
  • Sensorineural hearing loss — caused by damage or malfunction of the cochlea or the auditory nerve, which can result from ageing, excessive noise exposure, diseases such as meningitis, and head injury. Loss of loudness and lack of clarity are the key symptoms. One in 1000 children are born with a congenital form. Causes may include an inherited hearing loss, premature birth, lack of oxygen, damage from viruses such as rubella, and jaundice.

By the time hearing loss is diagnosed, an individual has usually lost around 60% hearing range.

An audiologist or clinician can administer a series of hearing tests to determine the type of hearing loss.

Sounds will be transmitted through headphones (air conduction) and through the skull (bone conduction) at different frequencies and volumes. The results are plotted on an audiogram, which shows the levels at which various frequencies are audible for each ear.

By the time hearing loss is diagnosed, the individual has lost 60% of his or her hearing range. Moreover, ten years typically pass between detection of hearing loss and treatment.  Meanwhile, auditory brain circuits have had a decade of disuse. During this time, the brain has rewired itself, creating the symptoms of hearing loss so that simple amplification no longer works.

Hearing aids are not cheap and might require 6-8 adjustments to obtain maximum effectiveness and comfort. Hearing aids work best in quiet and one-on-one situations and less well in noisy environments. While hearing aids directly address damage in the ear, they won’t have an impact on pathological changes in the brain unless used early.

If hearing loss is diagnosed early enough, a hearing aid can help preserve what remains but even as hearing aids are improving, it’s important to have realistic expectations.

At present, sensorineural hearing loss cannot be cured, but a hearing device can help. For moderate hearing loss, there are different types of hearing aids and an audiologist can advise which is most suitable.

For the profoundly deaf, a cochlear implant may assist. This device transmits sound directly into the auditory nerve via electrodes surgically implanted into the cochlea. Recipients will need to learn how to integrate the electronic sounds produced by the implant with lip reading skills.

This content is provided for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. If you have any concerns or questions about your health, please consult a suitably qualified healthcare professional.