Ocular surface area and human eye blink frequency during VDU work: the effect of monitor position and task.

The purpose of this study was to investigate how the ocular surface area (OSA) and the eye blink frequency (BF) are affected by a high versus a low-monitor position during visual display unit (VDU) work with varying cognitive demands. In a balanced randomized (2 x 2) design ten healthy subjects (five males, five females) completed two different tasks on the VDU in a simulated office environment (23 degrees C and 30-35% relative humidity); an active task with demands on vision and hand-eye coordination, and a passive task. Two monitor positions were used: high (the monitors' upper edge at the same height as the subjects' eyes) and low (lowered by 25 degrees and perpendicular to gaze angle). Each task lasted 10 min. An OSA-proxy was measured from video recordings, and BF was sampled by electrooculography. The effect of lowering the gaze angle by 25 degrees decreased the OSA-proxy significantly (P < 0.01) during the active task, indicating that a low position of the monitor may be preferable even though the BF also decreased. Overall, the OSA-proxy was 6% higher during the active task compared to the passive while BF during the active task was 69% lower than during the passive task. The low BF during the active task was succeded by a burst with high BF after cessation of the active task, indicating a compensatory blinking process. This stresses that interchange of work tasks with different cognitive load is as important as the monitor position in the prevention of visual and musculoskeletal disorders.