Poor binocular coordination of saccades in dyslexic children
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To examine the quality of binocular coordination of saccades in dyslexic children in single word reading and in a task requiring fixation of single LED.
Eighteen children with dyslexia (11.4 ± 2 years old) and 13 non-dyslexic children of matched age were studied. Horizontal saccades from both eyes were recorded with a photoelectric system (Oculomotor-Bouis).
Binocular coordination during and after the saccade in dyslexics is worse than that of non-dyslexic children; the disconjugacy does not depend on the condition. Moreover, dyslexics do not show the stereotyped pattern of disconjugacy (divergence during the saccade and convergence after the saccade). The conjugate post-saccadic drift is larger in dyslexics for both conditions.
Poor quality of binocular coordination of saccades and drift of the eyes after the saccade, regardless of the task, indicates an intrinsic ocular motor deficiency. Such a deficiency could be related to immaturity of the normal ocular motor learning mechanisms via which ocular motor coordination and stable fixation are achieved. Learning could be based on the interaction between the saccade and vergence subsystems. The cerebellum, but also cortical areas of the magnocellular stream such as the parietal cortex, could be the sites of ocular motor learning.
KeywordsDyslexia Children Binocular coordination Saccades Vergence
The authors are grateful to the Service de Psychopathologie de l’enfant et de l’adolescent (Dr. M.-F. Le Heuzey et Pr. M.-C. Mouren-Simeoni) at the pediatric hospital Robert Debré (referred center for a complete evaluation of the dyslexia state). The authors thank all children who participated in the study. F. Afkhami (orthoptist), J. Ayoun and F. Jurion (optometrists) conducted the visual examination of the children; Dr. R. Bertin corrected the linguistic content of the manuscript.
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