Summary

At the request of the Executive Office of the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST), a literature review was conducted to respond to a series of questions concerning the process that results in occupational hearing loss. The general objective of the project was to document how occupational hearing loss occurs, especially in relationship with presbycusis.

This review of the literature specifically aimed to (1) determine whether noise exposure can accelerate the progression of presbycusis; (2) establish whether using correction factors could make it possible to differentiate between occupational hearing loss and presbycusis; (3) evaluate how hearing loss progresses after the cessation of excessive noise exposure at work.

Some 30 studies published since 2000 and based on human or animal models were analyzed. The animal studies clearly demonstrated that exposure to noise accelerates the progression of presbycusis. The human studies reveal similar results. Several authors also submit that the classic concept that associates presbycusis solely with aging should be modified, and instead suggest that the loss of hearing observed with age is the result of the cumulative and synergetic effect of hearing impairment risk factors, among which is noise exposure.

Recent data, examined in this review of the literature, raise questions about the value of correction factors based on the premise that the slow degradation of hearing thresholds is only attributable to the intrinsic factor of aging, when there is evidence that some of this damage might be due to noise exposure. In the animal model, degeneration of anatomical structures related to hearing has been observed several months, even several years, after the cessation of exposure to noise. Some studies also show that impairment continues to progress beyond the simple effect of aging. While so far there are no longitudinal studies of the same nature among humans, research in this area is rapidly moving forward.