Square Wave Jerks in Chiari Type II Malformation

Chiari type II malformation (CII) is a congenital deformity of the cerebellum and brainstem. Square wave jerks (SWJ) are horizontal involuntary saccadic intrusions that interrupt fixation. Each SWJ is composed of an initial saccade that moves the fovea away from the intended position of fixation, followed after an interval by a saccade in the opposite direction, which re-foveates the fixation position. Cerebellar disorders may be associated with frequent SWJ or saccadic oscillations such as ocular flutter. The effects of CII deformity on fixation stability have not been investigated previously.