Retinal hazards from occupational blue light exposure to high intensity discharge lamps: A summary of relevant literature for development and action

Introduction
High-intensity discharge lamps (HID), such as halide lamps, have seen widespread use due to their high efficacy, excellent colour rendition and long service life. Compared to fluorescent and incandescent lamps, HID spectral emissions are shifted towards color temperatures of about 5000-6500 K°, thus increasing the amount of blue-light emission (up to 8%-22%), and potentially creating a blue light hazard for the retina. We sought to review the literature on reported exposures, effects and health surveillance for these lamps or similar sources.

Methods
The following topics were considered: physiopathology of the blue-light injury; occupational lighting risk assessment procedures; legislation, norms, and guidelines. Systematic searches were conducted using Medline and SCOPUS.

Results
The literature review shows that (i) cumulative blue light exposure over a lifetime can contribute to an irreversible damage of photoreceptors by enhanced photo-oxidative processes, (ii) no health surveillance procedures are currently implemented or proposed, (iii) occupational exposure could be substantially high for operators of TV studios, movie set, theatres and photo studios, (iv) only in Europe is there a specific legislation protecting workers on blue light hazards.

Discussion
According to present knowledge, lesions resulting from exposure to blue light cannot be differentiated from non-occupational lesions commonly observed in subjects suffering of age-related macular degeneration. Consequently, if blue-light lesions are developed, an ophthalmic examination would not reveal their potential link with occupational exposure. Two main issues emerge: the need for a long term (low level) exposure standard and health surveillance criteria (both for normal and susceptible individuals).