Time factors in VDT-induced myopia and visual fatigue: an experimental study.

In an experimental design with two matched groups (n = 13 and n = 17) working 2 and 4 hr respectively, followed by a 15-min restitution time, the study examined the effect of continuous VDT work on 1) visual acuity, refraction and oculomotor functions (ZCSV: zone of clear, single vision) and 2) the effect of 15-min restitution time on the oculomotor functions (ZCSV). In both groups there were a significant reduction in visual acuity, refraction changes in myopic direction and reduced ciliar and vergence muscle capacity. The ZCSV changes were temporary and a 15-min restitution period restored approximately half of the ZCSV changes. There were no significant differences between 2 or 4 hr of VDT work on any of the variables examined.