In this paper, the design and testing of the control of a new visual screener are described. The equipment is composed of a push-pull lever, an electronic digitalizer and a display on which Landolt rings are presented. The problem to be solved was to check whether the eight directions in which the lever could be oriented were equally reliable. For this purpose, 24 untrained subjects were required to respond to 108 by-chance oriented optotypes. This experiment demonstrated that the device was reliable in this respect that it produced very few errors; however, fiability was unequally distributed over the eight orientations. Suggestions for improvement were made.