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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.
Hearing loss that worsens with age but is caused by factors other than normal aging, such as noise-induced hearing loss, is not presbycusis, although differentiating the individual effects of multiple causes of hearing loss can be difficult. One in three persons have significant hearing loss by age 65; by age 75, one in two.
"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 impairment is defined by the World Health Organization (WHO) as a hearing loss with thresholds higher than 25db in one or both ears. The degree of hearing loss is classified as mild, moderate, severe or profound. [16] The results of pure-tone audiometry are however a very good indicator of hearing impairment.
There are four defined degrees of hearing loss: mild, moderate, severe and profound. Hearing loss may be divided into four types: conductive hearing loss, sensorineural hearing loss, central auditory processing disorders, and mixed types. Hearing loss may be unilateral or bilateral, of sudden onset or progressive, and temporary or permanent.
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 ...
The hearing loss of the individual is the average of the hearing loss values over the different frequencies. Hearing loss can be ranked differently according to different organisations; and so, in different countries different systems are in use.
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]