Square wave jerks--incidence, characteristic, and significance.

Square wave jerks (SWJ) are saccadic eye movements which, when recorded with open eyes are considered to be a pathological sign, caused by fixation instability, and pointing to a central neurological lesion. In reviewing 429 electronystagmographic traces, 85 (20%) were found to include the pattern of SWJ. Among them, in 38 traces, SWJ have been recorded with open eyes during fixation. Many of these cases were found to suffer from definite peripheral vestibular pathology, and some of them did not reveal any sign of neurological pathology in the clinical evaluation and by electronystagmography. Thus, SWJ are non-specific rapid eye movements, which do not necessarily point to neurological pathology. The literature is reviewed and the possible neural mechanism for the production of SWJ is discussed.