Visual fatigue in video display terminal operators: objective measure and relation to environmental conditions

The lighting conditions, luminance, contrast, and design of the workplace were studied in video display terminal (VDT) work stations operated by a group of female VDT data-acquisition clerks. VDT-induced symptoms were assessed by means of subject answers to a questionnaire. To measure VDT-induced ocular fatigue objectively, refraction power was determined before and at the end of workshift by an infrared autorefractometer. Job-induced refraction changes were then related to visual complaints and conditions in the workplace. The results confirmed that VDT data-acquisition work can lead to temporary myopia (myopization) in a remarkable percentage of operators; a significant correlation between eye discomfort, ocular asthenopia, and myopization was also found. Illumination levels, luminance, and contrast seem to be of paramount importance regarding visual symptoms: neither asthenopia nor myopization was observed when all of these conditions were adequate. If the ergonomic design of the workplace and the viewing distance are adequate, there are also usually fewer musculoskeletal symptoms. Our results suggest that changes in the ocular refraction status before and at the end of the work-shift, as determined by an automatic refractometer, provide a good objective index of VDT-induced "ocular fatigue", which in our study proved to be significantly related to workplace conditions.