Working with cathode-ray tube based visual display units

Eye strain when working with visual display units might be due to bad ergonomics but also to eye functions not meeting the demands. If the symbol on the screen has a 4 mm height and the working distance is 60 cm, a visual acuity of 0.4 is required. However to read with ease in the long run a visual acuity of 0.7 is needed. Therefore the employee's visual acuity and refraction must be examined when newly employed, at the age of forty, then every fifth year and when having problems. Other eye dysfunctions could be revealed from questionnaires.