Visual Ergonomics

Scientific literature offers no evidence to indicate that regular use of computer monitors threatens eye health or results in permanent vision damage. However, because of the increased demands on the visual system as a result of computer monitor use, computer users frequently complain of eyestrain, eye irritation, red eyes, burning, excessive tearing, blurred vision, or difficulty focusing. Uncorrected vision or old prescriptions may contribute to vision problems that a user experiences with sustained close work, especially when staring at a fixed object.

Some computer users report dry eyes, redness, burning, and excess tearing. The eye surface becomes dry because users tend to blink less and their tears evaporate faster during monitor use. Artificial tears used to supplement the eye's natural tear film alleviate symptoms for some computer users.

Specific prescription glass may be required for computer users to maintain a clear image. Bifocal wearers may experience positional problems since they often have to tilt their heads to focus through the bifocal segment. If individuals wear bifocals, they should inform the optometrist or optician about computer use when they are prescribed new glasses.

Images on the screen should not flicker or appear blurred. A monitor refresh rate of 70 Hz or greater is advocated to reduce noticeable flicker. Monitors that do not appear to be functioning properly should be evaluated by a competent technician and repaired or replaced as necessary.

The single most important factor in promoting comfort while working at a computer is the recognition that visual breaks are necessary. Users should rest their eyes periodically by turning them away from the screen and looking at something 25-30 feet away, by changing to an alternative task, or by closing the eyes for a few moments. The restorative power of a rest period depends on the type and duration of the breaks, as well as on the type and duration of the computer tasks they perform.

Glare can make using a computer monitor difficult and lead to vision complaints. At its worst, glare may totally obscure the image on a screen, requiring a greater visual effort. Monitor screens are particularly susceptible to two types of glare that may result from a variety of conditions.

  • Reflective glare is created by a mirror-like surface, such as the monitor screen, which may reflect overhead lights or an operator's bright clothing. (Detect by turning the monitor off and looking for reflections on the screen).
  • Direct glare results when a light source is shined directly to the eyes. The viewing surface, for example, may be obscured by the brightness from uncovered windows or other bright sources directly behind the terminal. This type of glare masks the display image.

Prevent Screen Glare

  • Do not place the monitor so the window is behind the screen, or directly facing windows. Ideally, the screen should be orientated so that it is perpendicular to the line of windows and rows of lighting fixtures.
  • Cover windows with drapes or blinds to limit the penetration of direct sunlight.
  • Consider attaching a glare screen.
  • Install recessed overhead lighting and special fixtures, where feasible.
  • Paint nearby walls in a dark or pastel color with a matte finish (less than 50% reflective), or add wall coverings on the wall directly behind the monitor screen.
  • Choose screen colors carefully. In general, use green and yellow and avoid red and blue.
  • Lower illumination levels for VDT tasks to approximately half the intensity of normal office lighting to reduce glare and eye strain. Ambient illumination in the room should be approximately 50 foot-candles (200 lux).
  • Contact the Physical Plant Area in charge of your facility to assist in lowering the light level (by removing every other bulb or by reducing the intensity of the bulb illumination).
  • Adjust the VDT brightness and contrast controls to increase character resolution.
  • Use additional task lighting for reading copy while the light intensity is lowered.