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Visual Fixation in Chiari Type II Malformation

Section of Pediatric Neurology Children's Hospital, University of Manitoba, Winnipeg, Manitoba, msalman@ hsc.mb.ca

James A. Sharpe, MD, FRCPC

Division of Neurology, University Health Network, Toronto, Ontario, Canada, Division of Vision Science Research Program, University Health Network, Toronto, Ontario, Canada, The Hospital for Sick Children, University of Toronto Toronto, Ontario, Canada

Linda Lillakas, BA

Division of Vision Science Research Program University Health Network, Toronto, Ontario, Canada

Maureen Dennis, PhD

Division of Psychology, University of Toronto Toronto, Ontario, Canada, The Hospital for Sick Children, University of Toronto Toronto, Ontario, Canada

Martin J. Steinbach, PhD

Division of Vision Science Research Program University Health Network, Toronto, Ontario, Canada, The Hospital for Sick Children, University of Toronto Toronto, Ontario, Canada

Chiari type II malformation is a congenital deformity of the hindbrain. Square wave jerks are horizontal involuntary saccades that interrupt fixation. Cerebellar disorders may be associated with frequent square wave jerks or saccadic oscillations such as ocular flutter. The effects of Chiari type II malformation on visual fixation are unknown. We recorded eye movements using an eye tracker in 21 participants with Chiari type II malformation, aged 8 to 19 years while they fixated a target for 1 minute. Thirty-eight age-matched healthy participants served as controls. Square wave jerks' parameters were similar in the 2 groups. Saccadic oscillations were not seen. Chiari type II malformation is not associated with pathological square wave jerks or abnormal saccadic oscillations. The congenital nature of this deformity may permit compensation that preserves stable visual fixation. Alternatively, the deformity of Chiari type II malformation may spare parts of the cerebellum that usually cause fixation instability when damaged.

Key Words: visual fixation • square wave jerks • saccadic intrusions • saccadic oscillations • Chiari type II malformation

Journal of Child Neurology, Vol. 24, No. 2, 161-165 (2009)
DOI: 10.1177/0883073808322326


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