Accumulation of VDT work-related visual fatigue assessed by visual evoked potential, near point distance and critical flicker fusion.

To confirm daily accumulation of visual fatigue induced by work with visual display terminals (VDT), visual evoked potential (VEP), near point distance (NPD) and critical flicker fusion (CFF) were measured in three VDT workers and three sex- and age-matched controls (non-VDT workers) in the morning, noontime and evening for five consecutive days (Monday to Friday), totally 15 times per subject. The workers had been engaged in wireless handling operation, with VDTs, of an unmanned power shovel (Worker 1), an unmanned 78-ton dump truck (Worker 2) and mobile monitor-cameras (Worker 3), for 10 months. Their working hours were about 6.5 hours per day; but, the Worker 2 could take a 10-minute recess (a period without VDT work) per about 30 minutes during working hours. Significant daily variations in the VEP latency, NPD and CFF were found in the Worker 1 or Worker 3 despite the absence of any significant daily or diurnal variations in the non-VDT workers; the trends in the variations were getting worse from Monday to Friday. The NPD in the VDT workers was significantly longer than that in each of the matched controls; also, the CFF in the Workers 1 and 3 was significantly depressed. The changes in the VEP latency from morning to noontime and in the NPD and CFF from noontime to evening were significantly larger in the VDT worker than in the matched control. These findings suggest that VDT work probably affects visual function assessed by the VEP, NPD and CFF. Visual fatigue due to long-term VDT work may tend to be accumulated day by day.