By Marcello Cherchi, MD PhD
For clinicians
Square wave jerks (SWJ) are small involuntary horizontal eye movements (≤0.5 degrees) that take the eyes off target, then after a brief intersaccadic interval, return the eyes to the target. Some investigators suggest that SWJ are “enhanced microsaccades and are closely related to the instability of the fixation eye movements” (Ohtsuka et al. 1986). The neuroanatomical substrate of SWJ is not well understood, though a control systems analysis proposed a model involving a leaky neural integrator (Suzuki et al. 2003).
Shallo-Hoffmann and colleagues (Shallo-Hoffmann, Petersen, Muhlendyck 1989) report that SWJ are more prominent in darkness and with the eyes closed; they are less prominent when the subject is fixating on a target.
Some investigators report that SWJ are more common in children (Salman et al. 2008), while other investigators report no clear correlation with age (Shallo-Hoffmann, Sendler, Muhlendyck 1990).
SWJ can be more pronounced in specific diseases, such as:
- Cerebellar disease (Daroff 1977)
- Cerebral lesions (Sharpe, Herishanu, White 1982)
- Friedreich’s ataxia (Dale, Kirby, Jampel 1978)
- Multiple sclerosis with brainstem involvement (Dell’Osso, Troost, Daroff 1975)
- Multiple system atrophy (Fukazawa et al. 1986)
- Parkinson’s disease (Rascol et al. 1991; White et al. 1983)
- Progressive supranuclear palsy (Fisk et al. 1982; Troost and Daroff 1977)
- Spinocerebellar degenerations (Yamamoto, Saito, Sobue 1988)
- Tobacco smoking (Sibony, Evinger, Manning 1988; Thaker et al. 1991)
There are rare reports of vertical square wave jerks occurring in neurodegenerative disorders such as Gaucher disease (Biegstraaten et al. 2011), Huntington’s chorea (Bollen et al. 1986) and Friedreich’s ataxia (Fahey et al. 2008). The mechanism of vertical square wave jerks is unknown, but experimental studies in monkeys suggest that it can result from lesions in the nucleus reticularis tegmenti pontis (Averbuch-Heller et al. 1996).
References
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Biegstraaten M, van Schaik IN, Aerts JM, Langeveld M, Mannens MM, Bour LJ, Sidransky E, Tayebi N, Fitzgibbon E, Hollak CE (2011) A monozygotic twin pair with highly discordant Gaucher phenotypes. Blood Cells Mol Dis 46: 39-41. doi: 10.1016/j.bcmd.2010.10.007
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