The above display should allow quantitative testing in subjects with hemifield depressions. Select the field area to be tested in the Hemifield menu and deselect dimming. Set the lead angle to zero by repeatedly tapping the left or right mouse buttons. Begin with a rotation rate of 20 or 30 RPM. Ask the subject to fixate on the center dot and to try to decide whether the rotating bar is perfectly straight. If the bar appears to be bent, try to compensate the apparent bending by adding a lead angle, by clicking the mouse buttons.