Video Displays, Work, and Vision (1983) / Chapter Skim
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Appendix A: A Review of Methodology in Studies of Visual Functions
Appendix A: A Review of Methodology in Studies of Visual Functions
Pages 219-226
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From page 219... ...
that measured changes in visual function in subjects performing tasks at two different types of VDTs; it is not included here because insufficient detail for a review was provided in the brief published report. One study reviewed here also compared changes in measures of visual function in subjects performing VDT and hardcopy tasks.
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From page 220... ...
Gunnarsson and Soderberg measured changes in the near points of accommodation and convergence under normal and intensified conditions of VDT use. Questionnaires and interviews were also used to obtain information regarding symptoms of '~visual strain." The report argues that changes in the near point of convergence may be a useful objective measure of visual strain associated with VDT work.
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From page 221... ...
The comparison group, which showed almost no change in visual acuity following work, consisted of non-VDT workers performing traditional office work, mainly typing. Because the tasks performed by this group were quite different from the test protocol performed by the VDT group and because subjects in the two groups were not appropriately matched in other respects, no conclusions can be drawn regarding the relative effects of VDT and hard-copy displays on visual acuity.
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From page 222... ...
The study reports that outfocus time and infocus time were significantly higher for the CRT display and that both times increased as a function of time on task for both the CRT display and the hardcopy display. Neither outfocus nor infocus times differed significantly as a function of age.
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From page 223... ...
In view of the subjective nature and inherent variability and imprecision of this type of measure, there may be no practical significance in the small differences in mean outfocus and infocus times for the CRT display compared with the hardcopy display (mean outfocus time of 0.013 seconds longer and mean infocus time of 0.012 seconds longer for the CRT) , and the increase in outfocus and infocus times for both displays as a function of time on task may have no practical significance.
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From page 224... ...
Ostberg reported a statistically significant shift in the mean dark focus of the air traffic controllers from 0.94 diopter before work to 1.62 diopters following work; the air traffic controllers were also reported to show statistically significant reduced accommodative responses following work, becoming more myopic for distant targets and more hyperopic for near targets. Absolute values of changes in accommodative response were not reported; however, examination of the graphs indicates that the values were fairly small.
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From page 225... ...
This value approximates the dark focus for many individuals (Leibowitz and Owens, 1978) and thus should not require unusual accommodative effort; it is also similar to the reported mean dark focus of the air traffic controllers measured following work (1.62 diopters)
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From page 226... ...
The data for the two telephone group~-each of which performed a different type of task, with a different amount of actual VDT work, presumably in a different working environment (~e working environments were not described) , on a different type of video display of unreported design—were pooled, and the average values were compared with average values obtained for the air traffic controllers, who performed tasks of a different nature for a specified period of time (2 hours)
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