Postural control in children with early strabismus without amblyopia

Purpose In healthy subjects, the postural stability in orthostatic position is better when fixating at near than at far distance; increased convergence angle contributes to such effect. Children with strabismus present a deficit in vergence movements. The goal of this study was to evaluate the postural control in children in relation with the vergence angle while fixating at different depths, and also while making active vergence movements. Methods A TechnoConcept platform (Cereste, France) was used to record postural stability of 11 subjects (M= 11.18 years) with convergent strabismus and 13 (M=11.31 years) with divergent strabismus in 3 conditions: fixation at 40cm, at 2m and active vergence movement between two target at 20cm and 50cm. Results As for the controls, the standard deviation of medio-lateral body sway decreased with proximity for convergent strabismus but increased for divergent strabismus. Relative to fixation, vergence eye movements caused an increase of medio-lateral body sway for convergent strabismus but decrease for divergent strabismus. Yet, vergence eye movements were associated with the least variance of speed, indicating that less energy is needed to control body sway. Conclusion We conclude that the fixation depth at which postural stability is best in strabismus is that for which the appropriate vergence angle correspond to the strabismus angle. It might be mediated by preponderant eye movement signals related to the angle of strabismus. Reduction of variance of speed in the active vergence eye movement condition corroborates further such interpretation.