Two patients had nystagmus and periodic alternation of the null point. The striking clinical feature is an alternation of the preferred position of gaze from right to left with contraversive head position. Jerk nystagmus with the fast component in the direction of gaze accompanies efforts to move the eyes away from the null point. The condition is similar to but distinguishable from periodic alternating nystagmus, and, like the latter, it is found in patients with other signs of neurologic disease. Reports of only two possibly similar cases could be found in the ophthalmic literature, and it is concluded that the entity is a rare disorder of ocular motility.
Robb RM. Periodic Alternation of Null Point in Congenital NystagmusAssociation With Alternating Gaze Deviation and Esotropia. Arch Ophthalmol. 1972;87(2):169-173. doi:10.1001/archopht.1972.01000020171010