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Video display terminals: safe use guidelines.

Scientists have conducted extensive research on the health effects of Video Display Terminals (VDTs). While early investigations focused on visual fatigue and ocular complaints, in the late 1970s research began to examine radiation effects. Later, emphasis was placed on the potential hazards to human reproduction. Research has identified three ways that VDTs have potential to affect human health: radiation, ergonomic effects, and stress.

POTENTIAL HAZARDS

Radiation Effects

While components of the video display terminal are capable of generating electromagnetic radiation, researchers have concluded the emissions are well below the level of acceptable standards of occupational exposure.[1-5] Researchers have investigated the relationship between VDT use and adverse reproductive outcomes among females. The adverse reproductive outcomes considered include spontaneous abortions, intrauterine growth retardation, low birth weight, and birth defects. Most research concludes no significant excess of VDT use occurred among cases experiencing spontaneous abortions.[6-9] Goldhaber et al,[10] with contrasting conclusions, found small excess risks associated with VDT use ([is greater than] 20 hours per week) for spontaneous abortion and birth defects. However, reporting bias by cases may account for the difference. Windham et al[9] concluded VDT use, either moderate or heavy, did not significantly increase the risk of low birth weight. However, their results suggests an effect of heavy VDT use on growth retardation. No other studies regarding VDT use and intrauterine growth retardation have been published.

Ergonomic Effects

Ergonomic effects include visual and musculoskeletal complaints. Visual fatigue, the most common eye complaint reported, has no long-term effect and is not recognized as a clinical condition by opthalmologists. Environmental causes associated with visual fatigue include illumination of the task, characteristics of the objects viewed, and visual status. The cause of visual complaints may arise from the VDT itself, the environment lighting, or the VDT user's vision. The World Health Organization (WHO) endorsed three general recommendations regarding visual demands and VDTs: 1) worker vision should be corrected if needed; 2) VDTs should be designed to ensure high image quality, including resolution, display stability, display polarity, luminance, and contrast; and 3) lighting conditions of the environment, which are critical in eliminating visual discomfort such as reflection and glare, should also be properly adapted to the task to be performed.[11]

While visual complaints are most common, musculoskeletal complaints are frequently mentioned among VDT users. Typically reported are pains in the neck, shoulders, back, and wrists. The cause is usually attributed to posture. It is more likely that the pain results from one or more of the following factors: poorly designed desks and chairs, lack of exercise on the job, repetitive tasks, work pace, personal traits, and work stress.[12] Frequent changes in posture may alleviate musculoskeletal fatigue.

Stress

Musculoskeletal problems often can be a manifestation of various stressors. Stress has potential to affect human health when coupled with VDT operation. Mackay and Cox[13] defined stress as a perceptual-cognitive phenomenon rooted in psychological processes; and stress will arise when an individual's needs and values are not balanced by environmental supplies from the work environment. Stress arises when individuals perceive their own abilities as not matched by the job demands. Not all VDT operators are bothered with stress. Workers at high risk for stress are those who sit for long hours doing repetitive work.[13,14] Eason[14] suggests that the use of VDTs (commonly associated with office automation) has brought relief from previously boring work tasks and that those who experience stress from repetitive work represent a small group VDT users.

VDT PURCHASING GUIDELINES

When purchasing a VDT the buyer should consider several characteristics to reduce health compromising effects. These characteristics include resolution, dot pitch, refresh rate, and size.

Resolution. On-screen image quality is determined by the resolution and color capabilities of the computer and the VDT. Resolution is expressed in terms of pixels appearing on the VDT. Resolutions of 640 X 480 or 1,024 X 768 represent the number of columns by the number of rows. The higher the numbers, the sharper the image.

Dot pitch. Dot pitch is the distance between pixels on the VDT. The closer the dots are to each other, the brighter the image. A lower dot pitch number means the dots are closer together. A VDT rated with a .28 dot pitch will provide a brighter image than one with a dot pitch of .31.

Refresh rate. Refresh rate is the rate at which the image is redrawn. The cathode ray tube (CRT) in the VDT forms images by projecting a series of still frames very rapidly on a screen, even if the image is not animated. Higher refresh rates result in less flickering on the screen. A refresh rate of 75 Hz, or 75 frames per second, can adequately support most computing needs.

Size. Measured diagonally from one comer of the screen to another, VDTs commonly come in 14-, 15-, 17-, and 20inch sizes. Even one or two inches means a considerable increase in both width and height, and thus area of the screen. Larger VDTs are capable of displaying larger and easier to see images and there is more on-screen desktop work space for more windows and documents.

ERGONOMICS OF VDT USE

When planning an effective computer work station the video display terminal and the lighting should be considered. The offices of Information Technology and Health and Safety at the University of North Carolina at Chapel Hill, and the American Academy of Ophthalmologists, developed recommendations regarding use of VDT at work stations (Figure 1).[15,16] According to these recommendations, the VDT should sit directly in front of the user, with the top of the screen at eye level. The distance from the computer users eyes to the screen should be 18-30 inches. When using a color VDT choose a color scheme that is soothing to the eyes such as blues and greens and keep the VDT properly focused.

[Figure 1 ILLUSTRATION OMITTED]

Video display terminals are typically kept farther away and higher than the usual reading distance. Therefore, if the computer user requires glasses for reading, the American Academy of Opthalmologists suggests visiting the ophthalmologist to discuss the work station environment of the user, and if necessary, receive an additional eye glass prescription for the computer work station. In addition, the computer work station should have moderate, indirect lighting, approximately half the level of normal office lighting. There should be minimal contrast between the VDT and other lighting.

References

[1.] Cox EA. Radiation emissions from visual display units. In Pearce BG, ed. Health Hazards of VDTs? New York, NY: John Wiley & Sons; 1984.

[2.] Kavet R, Tell RA. VDTs: field levels, epidemiology, and laboratory studies. Health Physics. 1991;61 (1):47-57.

[3.] Pomroy C, Noel L. Low-background radiation measurements on video display terminals. Health Physics. 1984;46(2):413-417.

[4.] Stuchly MA, Lecuyer DW, Mann RD. Extremely low frequency electromagnetic emissions from video display terminals and other devices. Health Physics. 1983;45(3):713-722.

[5.] Weiss MM. The video display terminals -- is there a radiation hazard? J Occup Med. 1983; 25(2):98-100.

[6.] Bryant HE, Love EJ. Video display terminal use and spontaneous abortion risk. Int J Epidemiol. 1989; 18(1): 132-138.

[7.] Ericson A, Kallen B. An epidemiological study of work with video screens and pregnancy outcome: I. A registry study. Am J Ind Med. 1986;9:447-457.

[8.] Lindbohm ML, Hietanen M, Kyronen P, et al. Magnetic fields of video display terminals and spontaneous abortion. Am J Epidemiol. 1992; 136(9): 1041-1051.

[9.] Windham GC, Fenster L, Swan SH, Neutra RR. Use of video display terminals during pregnancy and the risk of spontaneous abortion, low birth weight, or intrauterine growth retardation. Am J Ind Med. 1990;18:675-688.

[10.] Goidhaber MK, Polen MR, Hiatt RA. The risk of miscarriage and birth defects among women who use visual display terminals during pregnancy. Am J Ind Med. 1988;13:695-706.

[11.] Marriott IA, Stuchly MA. Health aspects of work with visual display terminals. J Occup Med. 1986;28(9):833-848.

[12.] Council on Scientific Affairs. Health effects of video display terminals. JAMA. 1987;257(11): 1508-1512.

[13.] Mackay C, Cox T. Occupational stress associated with visual display unit operation. In Pearce BG, ed. Health Hazards of VDTs? New York, NY: John Wiley & Sons; 1984.

[14.] Eason KD. Job design and VDU operation. In Pearce BG, ed. Health Hazards of VDTs? New York, NY: John Wiley & Sons; 1984.

[15.] American Academy of Ophthalmology. Computer monitors and the eye. 1997. Available online at: http://www.eyenet.org/public/pi/eye_health/safety/ecm_vdts.html

[16.] University of North Carolina at Chapel Hill, Health and Safety Office. Ergonomics: posturing for safety. 1996. Available online at: http://www.adp.unc.edu/hs/hpage04.html

Compiled by Lisa N. Pealer, MHSE, Editorial Assistant, and Steve M. Dorman, PhD, MPH, FASHA, Assistant Editor for Technology, Journal of School Health, Dept. of Health Science Education, University of Florida, Gainesville, FL 32611-8210.
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Author:Pealer, Lisa N.; Dorman, Steve M.
Publication:Journal of School Health
Date:Sep 1, 1998
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