Fig. 15 Depiction of shifts of neutral zone or null (N) in congenital nystagmus. Tracing demonstrates an idealized nystagmus pattern with both eyes open (OU). Neutral zone extends over several degrees on either side of 0°. When gaze is directed laterally, nystagmus of increasing amplitude develops with fast phase in direction of gaze. Occlusion of right eye (RE) shifts zone to the right; at 0° there is left-beating nystagmus. Occlusion of left eye (LE) shifts zone to the left; at 0° there is right-beating nystagmus.