Proposal of an index to evaluate visual fatigue induced during visual display terminal tasks

The study described in this article was designed to evaluate visual fatigue induced during video display terminal (VDT) tasks. Newly developed equipment was used that can simultaneously measure pupillary change, focal accommodation, and eye movement. The changes in these 3 physiological measures, taken during a VDT task, were used to propose an index for evaluating visual fatigue. Through multiple regression analysis, an index to describe the psychological sense of visual fatigue was obtained. In this index, the minimum pupil diameter, velocity of focal accommodation for constriction, and width of focal accommodation were included. The results suggest that visual fatigue in VDT tasks can be evaluated effectively using both pupil diameter and focal accommodation. The index can be used to assess visual fatigue induced during a VDT task if the following 3 conditions are satisfied: 1. Head movement is limited and infrequent. 2. The task requires focal accommodation. 3. During the task, there is no outstanding change in the lighting environment such as luminous intensity or brightness.