Demographic changes have important implications for the quality of working life. Increasing age is often accompanied by changes in perceptual, cognitive and motor abilities. The scientifically proven decrease of visual acuity with age is of particular importance for computer work. In this paper, acuity of vision was measured using a standardized eyesight test called Rodatest 302. To investigate the age-induced change in visual acuity and its impact on human performance, a target detection experiment with well-known Landolt rings was conducted on the basis of three different font sizes (12, 16 and 22 arc minutes). The Landolt rings were displayed on a TFT LCD screen. 75 subjects aged between 20 and 72 years participated in the experiment. The number of correctly detected Landolt rings (hits), the number of wrongly detected Landolt rings (false alarms) and the response time of correct responses were measured. Results from analysis of variance show a strong effect of font size and a medium age-related effect concerning the response time of correct responses. The interaction effect of font size and age group shows that age-related differences in response time can be compensated by enlarging the font size from 16 to 22 arc minutes. Results from partial correlation analysis show that an age-differentiated adaptation of font size is recommended rather than an adaptation based on measurement of visual acuity.