Even the best posture and the most ergonomically correct workstation won't prevent muscular stress and fatigue if you sit for several hours in one position. Breaks from VDT work can help keep your eyes, mind and body refreshed and energized.

The National Institute for Occupational Safety ad Health (NIOSH) recommends taking a short break every couple hours of uninterrupted VDT work. (Check with your supervisor for your break schedule).
Experts also suggest brief, frequent, "microbreaks." These breaks are defined as time spent doing something other than work on a VDT. They don't have to involved leaving your workstation. Suggestions include: moving around, streching, doing non-VDT tasks, refocusing your eyes, etc.

The timing of such microbreaks is more important than the length. To be the most effective, a break should be taken prior to the onset of fatigue, rather than as a means of recuperating from it.