Proper ergonomic design and adjustment of the computer and the work environment
can increase productivity and worker comfort by decreasing the visual demands of the task. Overall display legibility is an important factor in visual performance. Screen brightness and contrast should be adjusted to provide balance with room lighting and maximum visibility. Lowering screen brightness will generally reduce problems related to image stability or character flicker. Regular cleaning of the computer screen according to manufacturers’ directions will remove dust and dirt that may also interfere with screen visibility.
The color of computer screen characters may also affect their ease of visibility. The color of the characters can affect how the eyes focus on the screen and may bring about the development of harmless, but annoying, after-images for some individuals. Monochrome, or single color, displays often provide more legible images for word processing or data entry/acquisition tasks. Negative contrast computer displays (dark letters on a light background) generally provide a more legible image than positive contrast displays (light letters on a dark background). Either black characters on a white background or white characters on a black background have been found to be more visible than green, yellow-orange, blue or red characters.
Adjustment of the workstation to meet the individual needs of the operator is also important for overall performance and comfort. Inadequate viewing distances and angles can impose the necessity for awkward postures when viewing a computer
screen. The appropriate distance from the eyes to the computer screen is determined, in part, by the size of the letters on the screen and the adjustability of the workstation. A viewing distance of 20 to 28 inches is generally recommended. The direction of gaze can also affect the eyes’ focusing ability. Accommodative amplitude has been shown to be reduced with elevation of the eyes. The higher gaze angles at many computer workstations result in viewing conditions for which the amplitude of accommodation is reduced thus placing greater strain on the eyes’ focusing mechanism. Also, as the direction of gaze moves downward, stress on the eye muscles is reduced. The eyes should be in a downward gaze of about 15o when viewing a computer screen. As a result, the top of the screen should be below the horizontal eye level of the operator and tilted back slightly (10o-20o) away from the operator.
Musculoskeletal problems related to head and eye postures when working at a
computer are common and can often be alleviated through proper workstation
adjustment. Workstation furniture should be adjustable and designed so that operators can easily change postures. Computers that have detachable keyboards, screens that can be tilted to a comfortable viewing angle and moveable document holders allow operators to arrange the work area to their particular needs.39 Older workers, because of visual changes such as presbyopia and increased susceptibility to glare, may be especially vulnerable to problems of poor workstation design. Some office environments have been implicated in causing eye irritation because of their dry atmosphere. The airtight environment also traps vapors and particulate matter from office furnishings. This can be a particular problem for contact lens wearers.
These problems can be further exacerbated by decreased blinking caused by staring at a computer screen. The use of computers is associated with a decreased frequency of blinking and an increased rate of tear evaporation, each of which contributes to dry eyes. The use of artificial tears can provide relief from dry eye symptoms in some cases. In addition, the width of the palpebral fissure, and hence the exposed ocular surface area, can be decreased by placing the computer monitor at a lower height.