Fig. 5 Unidirectional types of jerk nystagmus, mechanism unknown, including two with saccadic foveation (pure jerk and jerk with extended foveation) and two with slow eye movement (SEM) foveation (pseudocycloid and pseudojerk). The increasing velocity slow phases are common in IN. Note small and variable saccadic amplitude in pseudocycloid waveform and further reduction in pseudojerk waveform.