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Visual Fatigue and Video Display Terminals

This study included three experiments aimed at gaining a better understanding of the causes of visual fatigue (VF) resulting from continuous work on a computer screen. Three different tasks were used in the experiments. The first experiment used a specially-programmed enless computer game with highly complex, cluttered and colorful displays. In the second and third experiments, the participants were instructed to read a short novel with interspersed questions toensure that they actually read the material. The font size used in the third experiment was much smaller than the one used in the second experiment. The first two experiments yielded relatively little evidence of VF and of the accompanying subjective visual discomfort. The third experiment yielded more signs of VF. There was a significant decrease in CFF after the VF task, and both TA and TV (tonic acommodation and tonic vergence) in both eyes were closer after the task was completed. The subjective questionnaire also indicated a significant increase in visual discomfort following the task, as indicated by nine of the questions (out of 15). A multiple regression analysis was performed on the total differences in the nine questionnaire items that yielded significant difference before and after the VF task. The analysis found that four physiological measures taken before the VF task could account for about 80% of the variance in visual discomfort. Those four measures were Visual Acuity (VA), CFF, Pupil Size (PS) and IPD, with VA being the significantly greatest contributor to the high multiple-correlation. It should be noted that visual acuity was measured while the participants wore their glasses, indicating that those who suffered most from VF were those with improper corrections in their glasses or whose vision was not perfect but not corrected. If visual acuity was not corrected, there was a strong tendency to complain about visual fatigue. We therefore recommend that all personnel whose jobs require many working hours on a computer screen be tested for visual acuity. In cases of VA deficiencies, these emplyees will require new glasses. Periodic vision examinations are also highly recommended. 

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