The wide-spread use of video display units in many work places has led to an increase in ophthalmologic examinations of the operators. For this reason, instruments for visual test screening (for example Visotest) have become widely used. Nevertheless, the literature does not seem to offer any clarification about the utility of these instruments as epidemiological tools. The costs and benefits of visual screening programmes were estimated in relation to specific visual deficit prevalence in a differently age-structured population. Via epidemiological calculation, it was demonstrated that positive and negative predictive values, which are directly related to deficit prevalence, are more important than sensitivity and specificity calculations. In view of the disorders screened, a visual test with a low positive predictive value is more expensive than one with a low negative predictive value. A visual test for visual deficits screening does not appear to be advisable in young populations, where the true positives/false positives ratio is 1:4, whereas in older populations the ratio is 2:1.