The Hess screen test is useful in evaluating patients with paretic or paralytic strabismus who have normal retinal correspondence. The test uses red-green goggles, a special screen that has a red dot (or light) in 8 inner positions and 16 outer positions, and a green slit projector. At a test distance of 50 cm, the patient is asked to place the green slit light so that it appears to coincide with the individual red dots (or lights). The relative positions are connected by a straight line; usually, just the 8 inner dots (or lights) and the central point of fixation are plotted. The goggles are then reversed so the deviation with the other eye fixating can be recorded.