VDU WORK, CONTRAST ADAPTATION, AND VISUAL FATIGUE

Prolonged VDU work leads to a number of detrimental changes in visual performance and to frequent complaints about asthenopic, musculoskeletal, and other symptoms. The relationship between changes in contrast adaptation at five spatial frequencies and workrelated symptoms were studied in an experimental approach with two groups, one working 2 h (n = 13) and the other 4 h (n = 17). Both groups showed a significant reduction in visual acuity and contrast sensitivity, but there were no significant differences between working two or four hours. The relationship between contrast adaptation and symptoms showed a mixed pattern. For the 2 h group there was significant positive correlation between symptoms and all spatial frequencies. For the 4 h group there were mixed correlations between symptoms and contrast adaptation. The results offer only partial support to Lunn and Bank's hypotheses on contrast adaptation, accommodation control and visual fatigue symptoms. Contrast adaptation saturates after 1-2 h and induces a short term effect on visual fatigue. For longer work periods posture-ergonomic and oculomotor factors will penetrate and dilute the contrast sensitivity effect.