Types and Causes
Hearing loss can be classified as:
Conductive hearing loss - this occurs when problems in the middle ear prevent it from 'conducting' sound to the inner ear, where sounds are processed
Sensorineural hearing loss – this occurs when parts of the inner ear (e.g. the cochlear, the nerve) are damaged or destroyed, preventing it from processing sound.
Occasionally hearing loss is a combination of both of these, this is called mixed hearing loss.
Anatomy of the ear
Image courtesy of Hearing World
There are a variety of causes of hearing loss, these include:
Listen Hear! reported that a noise component was associated with 37% of hearing losses, the most common noise injuries were from workplace and recreational sources.
Occupational Hearing Loss
Sufficient exposure to noise in the work place can result in occupational hearing loss and relates to both the volume of the noise and the period of exposure. Workers are entitled to compensation for hearing loss if their workplace doesn’t meet occupational health and safety standards with regards to noise exposure.
Recreational Hearing Loss
Sufficient exposure to recreational noise can result in recreational hearing loss and again relates to both the volume of the noise and the period of exposure. Recreational noise includes any activity undertaken out of the work place, for example listening to music (concerts, clubs, personal stereos, MP3 players), undertaking household tasks (vacuuming, mowing the lawn) or walking along a busy road.
Acoustic shock and trauma
Acoustic shock is associated with headset operators in call centres, resulting from a sudden and unexpected burst of noise. This may be due to a mechanical failure of the phone line, or loud sounds from a caller. The long term effects of acoustic shock on hearing are still being investigated.
Acoustic trauma is associated with acute, intense, noise exposures – for example a bomb explosion, alarm system or artillery fire often resulting in hearing loss.
Age-related hearing loss, also called presbycusis, is the gradual loss of the ability to hear as we get older. This is partially due to the aging process but may also be related to lifetime exposure to noise or damaging chemicals.
Some individuals suffer early onset of hearing loss which may be due to greater exposure to damaging chemicals or noise. There are some suggestions that early onset presbycusis may also have a genetic basis.
Some babies are born with hearing loss due to genetic abnormalities that prevent the structures of the ear from developing normally.
Some babies are born with hearing loss due to maternal infections during pregnancy or problems during birth. Diseases such as meningitis in early years can also lead to hearing loss. These losses tend to be sensorineural.
Eustachian tube dysfunction and otitis media can lead to hearing losses in children and these are usually conductive loses. Ear disease (in particular otitis media) is especially common in Aboriginal and Torres Strait Islanders, and leads to significantly higher rates of hearing loss in these populations.
Some chemicals have been found to be Ototoxic; these substances may be taken for example in medicines or inhaled through fumes. The process by which this damage occurs is not well understood They may directly damage delicate structures of the ear, such as the hair cells that line the cochlear, or may simply predispose an individual to early onset presbycusis.