A study of ergonomic demands and visual system disturbances in video display terminal (VDT) work was conducted. A total of 905 employees of two state agencies who were VDT users completed a self administered questionnaire to obtain information on hours of VDT use, eye wear, symptoms of visual system strain, and demographic data. A sample of 40 VDT users were selected from the survey for workstation ergonomic analysis. Ergonomic factors such as gaze angle, frequency of switching gaze between the document and display, document and display reading distances, most comfortable display reading distances, visual angle to direct glare sources other than the VDT, presence of specular reflections on the display, degree of image visibility loss due to specular reflections, and illuminance at the display surface, keyboard, and desk top at VDT workstations were measured. Factor analysis of visual symptom items from the survey were used to define scales of perceptual disturbances and visual discomfort. Multiple regression techniques were used to evaluate the ability of ergonomic factors, age and corrective eyewear use, and hours of daily use to predict visual disturbances arising from using VDTs. In the initial survey, visual strain generally decreased with eyewear use and increasing age. Besides age and eyewear use, near point of comfortable vision, most comfortable viewing distance, document distance, and gaze shift frequency were strongly correlated with ocular discomfort and perceptual disturbances. Video display reflections and direct glare in the visual field were not predictive of either strain parameter. The authors conclude that accommodative mechanisms are primarily responsible for inducing visual system strain in VDT users. Discrepancies in the distance of visual targets from one another and from comfortable viewing distances should be minimized to reduce accommodative demands.
The Changing Nature of Work and Workforce, Proceedings of the Third Joint US-Finnish Science Symposium, Frankfort, Kentucky, October 22-24, 1986, NIOSH, Cincinnati, Ohio