SUPERIMPOSED ANALOG VIDEO IMAGE ON PLOTTED DIGITAL FIELD TESTER DISPLAY

In an eye field tester, a vidicon camera observes the eye being tested and relays the resultant low light level image to the periphery of a digital display. The digital display contains both an image of the eye on the periphery and the plot of the visual field of the eye under test in the center. The vidicon observing the position of the eye has its horizontal and vertical sync pulses software generated to presettable counters. These counters generate corresponding delayed horizontal sync and vertical sync pulses for the vidicon. As a result of the delayed sync pulses, the central eye image of the vidicon is offset to the periphery of the digital screen (typically to the upper left-hand portion thereof). The offset image is gated into character spaces on the digital screen utilizing software generated character attribute.