Study of the relationship between lacrimation and blink in VDT work

VDT (Visual Display Terminal) work generates various symptoms in operators’ eyes such as strain, a sensation of dryness, the presence of a foreign body, and so on. Research suggests that lacrimal abnormality may be related causally to such symptoms. In this paper, the relationship between lacrimation (the secretion of tears) and the frequency of blink due to VDT work in health subjects and VDT workers with such symptoms, and consequent therapeutic methods, were studied. When lacrimation, BUT (Break-UP Time), and the frequency of blink before and after VDT work compared in the control subjects and VDT-operators, an essential difference was noted in experiment 1 the frequency of blink decreased only during VDT operation, and a decreasing tendency of lacrimation was also noted while lacrimation before operation was already less in the VDT group; no large variation was noted before or after VDT operation. The frequency of blink was relatively high during operation, and a decreasing tendency of BUT was noted, compared with that for control subjects. In experiment 2, lacrimation increased remarkably in four eyes (of two operators), and relief from the subjective symptoms was noted. However, BUT intactly reduced similarly before the use of a gelatin rod during the whole process. The insertion of a gelatin rod was consecutively carried out every two weeks for approximately eight months; the development of complications such as dacryosolenitis, etc., was not noted. From these results, it is considered that the insertion of a gelatin rod is clinically useful for VDT operators with decreasing lacrimation.     

Study of the relationship between lacrimation and blink in VDT work

VDT (Visual Display Terminal) work generates various symptoms in operators' eyes such as strain, a sensation of dryness, the presence of a foreign body, and so on. Research suggests that lacrimal abnormality may be related causally to such symptoms. In this paper, the relationship between lacrimation (the secretion of tears) and the frequency of blink due to VDT work in health subjects and VDT workers with such symptoms, and consequent therapeutic methods, were studied. When lacrimation, BUT (Break-UP Time), and the frequency of blink before and after VDT work compared in the control subjects and VDT-operators, an essential difference was noted in experiment 1 the frequency of blink decreased only during VDT operation, and a decreasing tendency of lacrimation was also noted while lacrimation before operation was already less in the VDT group; no large variation was noted before or after VDT operation. The frequency of blink was relatively high during operation, and a decreasing tendency of BUT was noted, compared with that for control subjects. In experiment 2, lacrimation increased remarkably in four eyes (of two operators), and relief from the subjective symptoms was noted. However, BUT intactly reduced similarly before the use of a gelatin rod during the whole process. The insertion of a gelatin rod was consecutively carried out every two weeks for approximately eight months; the development of complications such as dacryosolenitis, etc., was not noted. From these results, it is considered that the insertion of a gelatin rod is clinically useful for VDT operators with decreasing lacrimation.     

A longitudinal study of VDT work and health

A longitudinal study on the use of visual display terminals (VDTs) was conducted with questionaire data obtained 1981 and in 1987–1988 from a cohort of office workers. The use of VDTs became more widespread in these offices during the intervening time period, but the time spent by individuals working at VDTs showed no general increase. The data suggested that VDT use was related to the risk of developing eye discomforts and hand and wrist problems. For skin problems and headache, risks for VDT and non‐VDT users were fairly similar, but indications of increased risks were found for certain groups and situations. The risks of developing neck, shoulder, shoulder joint, or upper arm problems were high for both VDT and non‐VDT users, but there were, in this study, no convincing suggestions that these risks were higher for VDT users compared to nonusers.     

An analytical method for predicting perceived flicker

A method is described for predicting whether a visual display terminal (VDT) will appear to flicker given the display phosphor persistence, refresh frequency, luminance and other environmental factors such as the distance between the user and the VDT. Based on research on human temporal sensitivity (Kelly 1969), one can predict the maximum screen luminance and the minimum refresh frequency that will generate a flicker-free display for a theoretical standard observer. These predictions are tested across a range of refresh frequencies, screen luminance, screen phosphors and individual users.     

Objective evaluation of eye strain using measurements of accommodative oscillation

Accommodative oscillations occurring during eye strain induced by two different types of experimental visual search task—visual display terminal (VDT) work and conventional hard-copy (paper) work— were objectively measured using infrared optometry. The low-frequency component (0 to 1-5 Hz) of the accommodative oscillation was found to be significantly increased after the VDT work, but not after the paper work. At other frequencies there were no significant differences between the two work types and no significant effect of the task itself. In a questionnaire survey the subjects using the VDT complained more than the subjects given paper work of ocular symptoms such as eye strain and blurred vision. These results suggest that measurement of changes in accommodative oscillation, particularly the low-frequency component (0 to 15 Hz), may provide an objective parameter of eye strain.     

Winners and losers from computerization: A study of the psychosocial work conditions and health of Swedish state employees

This study was comprised of 1,738 state‐employed visual‐display terminal (VDT) users whose work environment and health were examined through questionnaires. The aim of the study was to analyze the relationship between work organization and mental/somatic symptoms. The results showed that work conditions vary considerably, both between groups of users and between men and women. Data‐entry tasks and a combination of data‐entry and data‐acquisition tasks were more common among women. The data‐entry group reported a greater number of somatic and psychological problems and contained the greatest percentage of people spending more than 6 hours per day at a terminal. There appeared to be a critical limit of 5 to 6 hours per day beyond which the incidence of symptoms rose sharply. Recommendations for preventive measures are presented.     

Eye strain resulting from VDT work at the Swedish telecommunications administration

A short experiment was carried out in the sales office and directory enquiries department of the Swedish Telecommunications Administration. VDT workload was set at two levels, a 'normal' level and an 'intensified' level. Visual strain associated with the work on VDTs was assessed by questionnaires and measurements of the near points of accommodation and convergence. When the VDT work routines were intensified an increase in subjective symptoms of visual strain was recorded. Increases in the near points of accommodation and convergence were recorded with intensified VDT workload. The experiment showed that organisational factors such as work spell duration and the rigidity of work routines seemed to play an important role in the frequency with which visual strain occurs in VDT work.     

Combined effects of working environmental conditions in VDT work

The combined effects of city noise and luminance of the computer display were evaluated from the changes in lymphocytes and mental activities of participants. Healthy male students were tested under the following four experimental conditions: (1) a calculating task on a video display terminal (VDT) with luminance of 90 cd m(-2) without city noise; (2) a calculating task on a VDT with luminance of 20 cd m(-2) without city noise; (3) a calculating task on a VDT with luminance of 90 cd m(-2) with city noise of 70 dB(A); and (4) a calculating task on a VDT with luminance of 20 cd m(-2) with city noise of 70 dB(A). A visual reaction test (VRT) was performed, and critical flicker fusion frequency (CFF), heart rate (HR), numbers of circulating white blood cells (WBCs), lymphocyte subsets and subjective symptoms of fatigue were measured (1) before; (2) just after; and (3) 30 min after each 60 min test. Subjective symptoms of fatigue significantly increased just after experiments conducted under the two noisy conditions. VRT and CFF showed significant changes in the case of the high-luminance display with noise. WBCs and neutrophils showed significant increases in the two quiet conditions. These results suggested that high luminance with noise had the most effect on subjective fatigue and mental activities.     

Work posture, workstation design, and musculoskeletal discomfort in a VDT data entry task

Self-report data on musculoskeletal discomfort were collected from several hundred VDT users in two agencies of a state government. Aspects of worker posture and workstation design were objectively assessed for 40 of the VDT users. Multiple regression analyses were used to examine the relationship between these ergonomic variables and musculoskeletal discomfort. Effects of ergonomic factors on musculoskeletal discomfort were clearly evident in the analyses. Regression models explained up to 38% of the variance in discomfort at different body sites. Of special interest was that leg discomfort increased with low, soft seat pans, suggesting that postural constraint is more important than thigh compression as a risk factor for leg discomfort in VDT work. In addition, arm discomfort increased with increases in keyboard height above elbow level, supporting arguments for low placement of the keyboard. Finally, high levels of neck and shoulder girdle discomfort observed in the study population suggest the need for further attention to the control of cervicobrachial pain syndromes in VDT work.     

VDT eyeglasses—multifocal lenses for near distance use

This paper discussed eyeglasses for middle-aged video display terminal (VDT) users and how middle-aged VDT users can obtain the proper eyeglasses for task that they perform in their office. First, the loss of visual function of middle-aged workers and the characteristics of modern eyeglass lenses are described in terms of VDT use. Then, a method for selecting the proper VDT glasses from an eyeglass shop was described. The discussion is particularly important in countries like Japan, where most workers do not have at their disposal experts to assist in the selection of the proper eyewear for their work-related tasks.     

Combined effects of working environmental conditions in VDT work

The combined effects of city noise and luminance of the computer display were evaluated from the changes in lymphocytes and mental activities of participants. Healthy male students were tested under the following four experimental conditions: (1) a calculating task on a video display terminal (VDT) with luminance of 90 cd m^-2 without city noise; (2) a calculating task on a VDT with luminance of 20 cd m^-2 without city noise; (3) a calculating task on a VDT with luminance of 90 cd m^-2 with city noise of 70 dB(A); and (4) a calculating task on a VDT with luminance of 20 cd m^-2 with city noise of 70 dB(A). A visual reaction test (VRT) was performed, and critical flicker fusion frequency (CFF), heart rate (HR), numbers of circulating white blood cells (WBCs), lymphocyte subsets and subjective symptoms of fatigue were measured (1) before; (2) just after; and (3) 30 min after each 60 min test. Subjective symptoms of fatigue significantly increased just after experiments conducted under the two noisy conditions. VRT and CFF showed significant changes in the case of the highluminance display with noise. WBCs and neutrophils showed significant increases in the two quiet conditions. These results suggested that high luminance with noise had the most effect on subjective fatigue and mental activities.     

The influence of VDT work on musculoskeletal disorders

Relationships between visual display terminal (VDT) use and musculoskeletal problems were examined in a group of 353 office workers, using data from medical and workplace investigations as well as questionnaires. There were no general differences between VDT and non-VDT users as to the occurrence of muscle problems. Combinations of specific VDT work situations such as data entry work or work with a VDT for more than 20 h/week and the presence of some other factors were, however, associated with excess risks of certain muscle problems. The extraneous factors involved in the definitions of such risk groups were: use of bifocal or progressive glasses at a VDT; stomach-related stress reactions; limited rest break opportunity, repetitive movements; non-use of lower arm support; and possibly the vertical position of the keyboard; and presence of specular glare.     

Biomechanical aspects of sitting: An application to VDT terminals

In order to avoid musculoskeleta! problems when working at a VDT terminal, biomechanical aspects of sitting and of working in a sedentary position need to be considered. This papers reviews relevant biomechanical knowledge and relates it to field studies of VDT users and their preferred workstation settings. It is concluded that even though good agreement exists between subject comfort rating and preferred postures on the one hand and biomechanical data on the other, an ergonomic work organization is necessary to achieve the best possible work conditions.     

Workstation variables and visual discomfort associated with VDTs

We have investigated the effects of a range of workstation factors upon the visual symptoms experienced by a group of 92 visual display terminal (VDT) users. Subjects in the study kept a diary over five consecutive working days in which they recorded the types of visual and postural symptoms which occurred and the types of work tasks being performed. Each subject's workstation was analysed for screen legibility and stability, discomfort and disability glare, and required head postures. By the use of multiple regression analysis techniques we have considered the relative contribution of these factors to the symptoms reported by the users of these workstations. Screen legibility significantly influenced the occurrence of symptoms of ocular discomfort and vertical head movements significantly affected the incidence of postural/headache symptoms.     

Effect of job demands and social support on worker stress: a study of VDT users

This study examined the effect of job demands (quantitative workload and computer-related problems) and social support (supervisor and co-worker support) on stress of VDT users. A survey questionnaire was administered to employees of three public service organizations. Two-hundred and sixty-two office workers participated in this study. Results showed that job demands (quantitative workload and computer-related problems) had a direct effect on psychological complaints of VDT users. On the other hand, co-worker support did not affect worker stress. Supervisor support was a buffer against worker stress both in the low and high job demands conditions. However, supervisor support did not have any interactive buffering effect on the relationship between job demands and worker stress.     

Mental and physical strain at VDT workstations

. There are millions of workers worldwide who use video display terminals (VDTs) on a daily basis. Over the past decade VDT users have reported a variety of health complaints that have been associated with VDTs including visual and musculoskeletal discomfort and psychological distress. In addition VDT users have expressed fears about radiation from VDTs and more recently concerns about adverse reproductive effects. This paper explores the potential health effects of working at a VDT based on an evaluation of current research literature and indicates where more research is underway or needed to better define health risks. Some conclusions about the seriousness of potential health effects are presented.     

The relation of vergence effort to reports of visual fatigue following prolonged near work

Two experiments examined the link between vergence effort and subjective reports of visual fatigue following prolonged near work. In Experiment 1, dark vergence and reports of visual fatigue symptoms associated with computer use were measured in 104 persons. Dark vergence was significantly correlated with four of six symptoms of visual fatigue. In Experiment 2, 16 subjects who exhibited clear "Heuer effects" (systematic gaze-related changes in dark vergence) read from a video display terminal (VDT) at a distance of 20 cm for 60 min under two gaze elevation conditions: 20 deg above and 20 deg below a baseline gaze elevation. This manipulation was designed to vary the amount of vergence effort required to fixate the VDT. Results indicate a positive relation between vergence effort and visual fatigue both within and between subjects, and that prolonged near work leads to decreased vergence accuracy at far distances. Implications for VDT workstation design are discussed.     

Occupational stress factors in visual display terminal (VDT) operation: a review of empirical research

A review of the literature involving empirical research (experimental and field investigations) on stressful aspects of visual display terminal (VDT) operation is presented. Studies reviewed included assessment of visual fatigue and/or performance, musculoskeletal symptoms and operator attitudes towards job demands and quality of working life. In addition, some investigation included discussions and evaluations of the physical attributes of VDT workplaces; including ergonomic factors (task lighting, glare conditions, anthropometric configuration of VDT and accompanying furniture), environmental factors (temperature, humidity, radiation) and psychosocial factors (job demand, work content, work-rest schedules).

The literature reveals that levels of visual and musculoskeletal complaints among VDT operators are high. Moreover, ergonomic field assessment of VDT workplaces indicate that the majority of those examined were suboptimal with respect to existing recommendations regarding lighting, glare control and anthropometric dimensions of screen, keyboard, desk and chair. Nevertheless, evidence of causal linkages between specific ergonomic attributes of the workplace and specific patterns of symptomatology are lacking.

Finally, work demand and task structure attributes to the VDT operation were demonstrated to have strong effects on incidences of reports of visual and postural symptoms as well as on psychosocial attitudinal indicators. Hence, it is argued that approaches toward stress reduction must include job content as well as ergonomic factors.     

A review of physical exercises recommended for VDT operators

This paper presents an evaluation of exercises that have been recommended for the prevention of musculoskeletal discomfort among VDT/office workers. 127 individual exercises were analysed for their suitability for performance in VDT workplaces. Additionally, each exercise was judged in terms of its safety and its compliance with principles of physiotherapy. Results showed that, in the majority of cases, the prepared instructions for the exercises were satisfactory and the exercises could be readily performed at the workstation. However, over a third of the exercises were conspicuous and potentially embarrassing to perform, and half would significantly disrupt the work routine. Additionally, a number of the exercises posed potential safety hazards, exacerbated biomechanical stresses common to VDT work, or were contraindicated for persons with certain health problems. These findings suggest a need for greater attention to both the practical and the therapeutic aspects of exercises promoted for VDT users.