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Occupational noise exposure is the main risk factor for work-related hearing loss. One study examined hearing test results obtained between 2000 and 2008 for workers ages 18–65 who had a higher occupational noise exposure than the average worker. [153] Of the sample taken, 18% of the workers had hearing loss.
Ototoxicity-induced hearing loss typically impacts the high frequency range, affecting above 8000 Hz prior to impacting frequencies below. [8] There is not global consensus on measuring severity of ototoxicity-induced hearing loss as there are many criteria available to define and measure ototoxicity-induced hearing loss.
Noise-induced hearing loss is a permanent shift in pure-tone thresholds, resulting in sensorineural hearing loss. The severity of a threshold shift is dependent on duration and severity of noise exposure. Noise-induced threshold shifts are seen as a notch on an audiogram from 3000 to 6000 Hz, but most often at 4000 Hz. [16]
PTA can be used to differentiate between conductive hearing loss, sensorineural hearing loss and mixed hearing loss. A hearing loss can be described by its degree i.e. mild, moderate, severe or profound, or by its shape i.e. high frequency or sloping, low frequency or rising, notched, U-shaped or 'cookie-bite', peaked or flat.
Hearing loss has multiple causes, including ageing, genetics, perinatal problems and acquired causes like noise and disease. For some kinds of hearing loss the cause may be classified as of unknown cause. [citation needed] There is a progressive loss of ability to hear high frequencies with aging known as presbycusis. For men, this can start as ...
"Conventional" pure tone audiometry (testing frequencies up to 8 kHz) is the basic measure of hearing status. [6] For research purposes, or early diagnosis of age-related hearing loss, ultra-high frequency audiograms (up to 20 kHz), requiring special audiometer calibration and headphones, can be measured. [7]
Hearing loss due to chemicals starts in the high-frequency range and is irreversible. It damages the cochlea with lesions and degrades central portions of the auditory system . [ 45 ] For some ototoxic chemical exposures, particularly styrene, [ 46 ] the risk of hearing loss can be higher than being exposed to noise alone.
Conductive hearing loss due to disorders of the middle ear shows as a flat increase in thresholds across the frequency range. Sensorineural hearing loss will have a contoured shape depending on the cause. Presbycusis or age-related hearing loss for example is characterized by a high frequency roll-off (increase in thresholds).