Contrast sensitivity and the near point of accommodation after work with a visual display unit

After several hours of work with a visual display unit (VDU), operators become myopic for a short time. Such transient myopia may be evaluated by measuring contrast sensitivity to a modulated grating pattern. The aim of the present study was to determine whether there are any accumulative myopic effects after 1 day of VDU work. We examined grating contrast sensitivity in a group of 13 full-time workers and in 13 office employees who used VDUs only sporadically. The results, which were compared with the near point of accommodation, clearly illustrated that there is no decrease in contrast sensitivity. In the VDU group the decrease in the near point of accommodation was uniformly distributed between zero and 1.0 diopter, whereas among the non-VDU workers 77% of the decrease was between zero and 0.25 diopter. We conclude that the myopic changes in the refractive status of operators after VDU work are not evident in a decrease in contrast sensitivity. However, in VDU workers the dynamic range of accommodation was smaller, suggesting that the visual fatigue and visual stress that developed at work hindered visual activities after work.