[Computer display work and rest position of the vergence system]

Subjects with different characteristics of the vergence system resting state (close or distant resting vergence, large and small increase upon depression of the eyes) worked with a VDU in a relatively high and a relatively low position for 1 1/2 hours. The directions of gaze were about -5 degrees and -35 degrees below the horizontal. A shorter observation distance was chosen with the lower VDU position than with the higher one, and it increased during the course of the work. In the high VDU position the increase was particularly strong for subjects with a distant resting vergence. The discrepancy between the angle of convergence during visual work and the resting vergence was larger in subjects with a distant resting vergence than in subjects with close one, and it was larger with the higher than with the lower VDU position (except in subjects with a minimal effect of eye depression on resting vergence). However, corresponding differences in visual fatigue as assessed by means of a questionnaire could not be found. Nevertheless the majority of subjects preferred the low VDU position. A number of additional consequences of a low VDU position support the conclusion that it would be advantageous for many users to tilt the display backward and to sink it below the level of the table surface.