Color of visual display terminals and the eye. Green VDTs provide the optimal stimulus to accommodation

Screen Color and Reading Performance on Closed–Circuit Television

To investigate whether screen color is an important variable in the prescription of CCTV systems, the author measured the visual performance of CCTV users on white, green, and amber screens. When the screen luminance and contrast were equated for each CCTV, the users’ reading performance was unaffected by the screen color. Although some individuals expressed a clear subjective preference or dislike for one color or another, there was no obvious link between the cause of low vision and preference for or aversion to that color.

Steady-state accommodation response and VDT screen conditions

Steady-state accommodation response was measured for seven different visual display terminal (VDT) screen conditions and a hard-copy control condition. The screen conditions included variations in screen polarity, contrast and chromatic characteristics of the text and background. Accommodation response was measured for seven young subjects using a free-space infrared optometer, the Canon Autoref R-1. The accommodation response was measured every 1.3 s over a period of 60 s for each test condition, and both the mean and standard deviation of the responses were derived. A small but significantly higher accommodation response was found for hard copy, blue-on-red and red-on-blue screen conditions compared with white-on-black, green-on-black and black-on-white screen conditions. Screen polarity and contrast had little effect on accommodation response for the black-and-white screen conditions. The variability of accommodation response showed little difference between test conditions. For short-term VDT screen viewing, the accommodation response appears to be relatively accurate and stable across a wide range of screen conditions.

Accommodative responses to naturalistic stimuli

Steady-state accommodative responses to a wide range of commonly encountered textural and graphic stimuli were investigated in 12 young, visually normal subjects. Details of two experiments are described. In the first experiment, stimuli were varied in terms of size, contrast, spatial frequency, colour and intellectual demand. In the second experiment, only the colour of the targets was systematically altered. In both experiments the stimulus demand was maintained at 3 D, and accommodation was measured subjectively using a Hartinger coincidence optometer. No significant difference in mean accommodative response was observed between the widely differing targets adopted in either experiment. These findings suggest that an overall threshold exists for accommodative stimuli, with supra-threshold targets of low to moderate contrast being capable of initiating and sustaining an appropriate accommodative response.

Video display units and visual function

The widespread use of visual display units (VDU) in the workplace has engendered visual complaints and concern for workers' health and safety. The detectable levels of radiation emitted from VDUs have been well below safety levels and exposure to VDUs does not appear to cause any organic damage to the eye. However, visual disturbance and eye discomfort affects many workers using VDUs, and these symptoms may be alleviated by a number of measures, including proper diagnosis of pre-existing ocular problems, use of special eyeglasses, and correct arrangement of lighting and furniture in the work area.