NIHL: Asymmetrical Hearing Loss

24 April 2019

Noise Induced Hearing Loss (NIHL) usually develops gradually after years of exposure to loud noise in a working environment. NIHL almost always is bilateral and affects both ears equally and is usually considered to cause similar amounts of damage to both ears, since most occupational noise is symmetrical.

Asymmetrical loss is where Air conduction thresholds show a significant difference between the ears particularly in the higher frequencies and this usually does not represent a case of noise related hearing loss. Obviously minor differences are bound to show due to the nature of the audio test itself as well as various audiometric errors. If the threshold differences are more than 10dB between the thresholds then this will usually be deemed as an asymmetrical audiogram. As aforementioned NIHL is usually symmetrical and therefore if a person has symmetrical hearing loss does this mean he is not suffering from NIHL?

No. Asymmetrical loss could be caused by various reasons such as greater hearing loss in one ear, for example, if a person was a HGV driver with the engine in the cab in the 1970s, he would obviously be exposed to more noise to his left ear than the right and therefore his audiogram would show loss probably to be asymmetrical. Or if a person is working in a factory and provided with a properly fitted right ear plug but the left is not in good working order he could also show asymmetry. Another example could be where a person has wax in one ear this could reduce the transmission of noise and therefore be less damaging to that particular ear. This obviously, could become a matter for the medical experts to provide reasoning behind the asymmetrical loss as sometimes the reason could even be unknown.

Also, people vary in their susceptibility to both age-related hearing loss and NIHL. While age-related hearing loss is inevitable, noise damage is still needed to be prevented and protected, by adequate hearing protection and hearing conservation programmes being in place in the workplace.

Evidence from recent studies shows that noise exposure can result in asymmetric hearing loss due to unique differences in susceptibility to noise damage and various reasons as discussed above. Appropriate prevention programmes and adequate hearing protection is important to prevent or mitigate NIHL.


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