Postural control in nonamblyopic children with early-onset strabismus

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.

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.

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.

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.