How to place the computer monitor: measurements of vertical zones of clear vision with presbyopic corrections.

BACKGROUND

This study intended to measure the near and far points of clear vision as a function of the inclination of the line of sight with comfortable head posture. Measurements with different lenses for presbyopic correction were made to suggest comfortable positions of the monitor for computer work.

METHOD: An 'inclined optometer' was built, including a concave mirror to shift a visual target of constant angular size from near to infinity (proposed by Reiner). The optometer could be inclined vertically from horizontal to 50 degrees downward to vary the inclination of the line of sight. Measurements were made with a comfortable head position adjusted on a headrest.

RESULTS

The near and far points were plotted both in the unit one/metre as a function of eye inclination (optometric diagram) and also as positions from the eyes in workspace co-ordinates (workplace diagram). First, individual examples of plots of the vertical zones of clear vision at the workplace are shown. Second, the group mean data of 22 observers with newly prescribed lenses showed that the vertical zones of clear vision for general purpose progressive addition lenses (PALs) reach infinity and are flatter, while computer vision PALs lead to more steep vertical zones ending at intermediate distances. Third, the mean results of three samples from our laboratory were compared with respect to general purpose PALs, which are most frequently used by presbyopic people.

CONCLUSIONS

The diagrams of the vertical zones of clear vision for different spectacles provide information on the ergonomic vertical position of computer monitors for clear vision with a comfortable head position. The grand mean of general purpose PALs suggests that the upper edge of the monitor should be at least approximately 15 cm below eye level at a typical viewing distance of approximately 75 cm. Higher monitor positions are possible with computer vision PALs.