C. Gaertner

Postural control in nonamblyopic children with early-onset strabismus.

PURPOSE In healthy subjects, the postural stability in orthostatic position is better when fixating at near than at far. Increase in the convergence angle contributes to this effect. Children with strabismus present a deficit in vergence. We evaluated postural control in children with respect to the vergence angle as they fixated at different depths, thereby engaging in active vergence movements. METHODS A TechnoConcept platform was used to record the postural stability of 11 subjects (mean age 11.18 ± 4.02 years) with convergent strabismus and 13 (mean age 11.31 ± 3.54 years) with divergent strabismus in 3 conditions: fixation at 40 cm, at 2 m, and active vergence movements between 20 and 50 cm. RESULTS The mediolateral body sway decreased significantly with proximity for convergent strabismus (from 3.78-2.70 mm) but increased significantly for divergent strabismus (from 3.27-3.97). Relative to fixation, vergence eye movements resulted in a statistically significant increase in mediolateral body sway for convergent strabismus (3.55 vs. 2.70) and a decrease for divergent strabismus (3.11 vs. 3.97, P = 0.047). Vergence eye movements were associated with the least variance of speed (99 mm(2)/s(2) for convergent and 117 mm(2)/s(2) for divergent strabismus), so less energy was required to control body sway. CONCLUSIONS The fixation depth at which postural stability is best is proximal for convergent strabismus and distal for divergent strabismus. Optimal postural stability might be mediated by preponderant eye movement signals related to the angle of strabismus. Reduction of variance of speed in the active vergence condition corroborates our hypothesis.

Benefit of Bi-Ocular Visual Stimulation for Postural Control in Children with Strabismus

Vision is important for postural control as is shown by the Romberg quotient (RQ): with eyes closed, postural instability increases relative to eyes open (RQ = 2). Yet while fixating at far distance, postural stability is similar with eyes open and eyes closed (RQ = 1). Postural stability can be better with both eyes viewing than one eye, but such effect is not consistent among healthy subjects. The first goal of the study is to test the RQ as a function of distance for children with convergent versus divergent strabismus. The second goal is to test whether vision from two eyes relative to vision from one eye provides better postural stability. Thirteen children with divergent strabismus and eleven with convergent strabismus participated in this study. Posturtography was done with the Techno concept device. Experiment 1, four conditions: fixation at 40 cm and at 200 cm both with eyes open and eyes covered (evaluation of RQ). Experiment 2, six conditions: fixation at 40 cm and at 200 cm, with both eyes viewing or under monocular vision (dominant and non-dominant eye). For convergent strabismus, the groups mean value of RQ was 1.3 at near and 0.94 at far distance; for divergent, it was 1.06 at near and 1.68 at far. For all children, the surface of body sway was significantly smaller under both eyes viewing than monocular viewing (either eye). Increased RQ value at near for convergent and at far for divergent strabismus is attributed to the influence of the default strabismus angle and to better use of ocular motor signals. Vision with the two eyes improves postural control for both viewing distances and for both types of strabismus. Such benefit can be due to complementary mechanisms: larger visual field, better quality of fixation and vergence angle due to the use of visual inputs from both eyes.

Up/Down Anisotropies of Vertical Saccades in Healthy Children From 6 to 10 Years of Age

PURPOSE Although the overall development of saccades in children has recently gained increasing interest, the precise characteristics of vertical saccades remain understudied. This study focused on the development of vertical saccades and their interaction with vergence movements. METHODS Thirty-one children (mean age: 7.33 ± 0.21 years) performed vertical saccades with an eccentricity of 7.5° at 40 and 150 cm viewing distance, in a simultaneous paradigm (simultaneous offset of central dot and onset of peripheral target). RESULTS The results revealed shorter latency, more vertical conjugate postsaccadic drift after upward saccades, and less horizontal vergence during and after upward saccades in children. Furthermore, the intrasaccadic convergence decreased progressively with childrens age for upward saccades. Relative to adult behavior, children present more hypometric saccades, longer latencies, higher vertical disconjugacy, and a different pattern of horizontal vergence during vertical saccades. CONCLUSIONS This result suggests that up/down asymmetries are built progressively in mutual interaction with a perceptive peripheral bias such as up being perceived as far and down as near.

Education Influences Creativity in Dyslexic and Non-Dyslexic Children and Teenagers

Background and Study Hypothesis Are dyslexic children and teenagers more creative than non-dyslexic children and teenagers? Whether creativity is higher in dyslexia, and whether this could be related to neurological development specific to the dyslexic disorder, or to compensatory strategies acquired later in life, remains unclear. Here, we suggest an additional role of differential educational approaches taken in each school that could either enhance or suppress an already higher baseline creativity of dyslexic children and teenagers. Results Creativity in dyslexic and non-dyslexic children and teenagers from different schools in France and in Belgium, as well as in students from different universities, was evaluated with the Torrance Test of Creative Thinking (TTCT). Children and teenagers with dyslexia and/or with other similar dysfunctions showed higher creativity scores than non-dyslexic participants. Moreover, the educational approach could further enhance the creative scores in dyslexia, which could be as high as those measured in students from art universities. Conclusions We conclude that dyslexic children and teenagers can be highly creative. Yet, expression of creativity can be modulated by educational approach, indicating a probable advantage for personal follow-up compared to normalizing education strategies.

Up/down anisotropies of vertical saccades in healthy children depending on the mode and the depth of execution.

While the overall development of saccades in children has recently gained increasing interest, the precise characteristics of vertical saccades remain understudied. The few adult studies existing showed up/down anisotropies on various parameters. This study focuses on the development of vertical saccades and their interaction with vergence movements, according to the mode of initiation of the saccades (automatic and controlled). Eighty six children (9.57 ± 3.15 years) performed vertical saccades with an eccentricity of 7.5°, at 40 cm and at 150 cm viewing distance, in a gap paradigm – automatic saccades – and in an overlap paradigm – more voluntary or controlled saccades. Task and direction effects: latency was overall longer in the overlap than in the gap task, duration was longer for upward than downward saccades, conjugate vertical drift was larger after upward than downward saccades, horizontal vergence was higher during and after downward than upward saccades. Age effects: For upward saccades, amplitude, mean and peak velocity of upward saccades increased with age, while the vertical conjugate drift after downward saccades at far distance decreased with age; for downward saccades in the overlap task, the horizontal convergence increased with age concomitantly with an increase of the duration. The results are discussed in the context of hypothetical differential circuits of automatic and controlled saccades maturing progressively in children and interacting with direction (up/down). We suggest that the up/down asymmetries, more pronounced in the overlap task, are built progressively in mutual interaction with a perceptive peripheral bias, up being perceived as far and down as near.

Influence de l’extéroception plantaire sur les mouvements de vergence chez le sujet sain

INTRODUCTION : Le pied [1] et l’œil [2] sont deux entrees importantes du Systeme Postural, mais encore peu d’etudes se sont interessees a leur fonctionnement synergique. Hollands et al [3] ont toutefois mis en evidence une coordination corporelle generale, reliant les mouvements des yeux et des pieds. Plusieurs auteurs ont montre que les afferences proprioceptives (notamment des muscles extrinseques plantaires) influent sur le controle oculomoteur [4,5]. Des observations cliniques repetees laissent supposer que l’exteroception plantaire a elle aussi une telle influence (modification du Maddox). Cette etude vise a objectiver ces observations.