Binocular coordination of saccades in children with strabismus before and after surgery

PURPOSE. To examine the quality of binocular coordination of saccades in children with various types of strabismus and the effect of strabismus surgery. METHODS. Eight subjects were tested (5-15 years old): five with convergent strabismus, three with divergent strabismus. A standard saccade paradigm was used to elicit horizontal saccades to target LEDs (5degrees to 15degrees). Saccades from both eyes were recorded simultaneously with the photograph-electric Skalar IRIS device (Delft, The Netherlands). This task was run before and about 3 weeks after strabismus surgery. RESULTS. Before surgery, the difference in the amplitude of the saccade between the left eye and the right eye was larger (15% of the saccade size) than in normal children of similar age. After strabismus surgery for all subjects the squint angle was reduced, and the amplitude of the disconjugacy of saccades decreased significantly, dropping to normal values (6%). As in normal children, postsaccadic eye drift (both its conjugate and its disconjugate components) was small in amplitude, The difference compared with normal subjects was that disconjugate drift did not restore the disconjugacy of the saccade itself (e,g., in normal subjects drift is convergent when saccade disconjugacy is divergent and vice versa). Rather, disconjugate drift tended to drive the eyes toward static eye misalignment (e.g., the drift was mostly convergent for convergent strabismics and divergent for divergent strabismics). Surgery had no significant effect on either component of the drift. CONCLUSIONS. The improvement of the binocular coordination of the saccades could be due, at least partially, to central adaptive mechanisms rendered possible by surgical realignment of the eyes. Separate mechanisms control the binocular coordination of saccades and the alignment of the eyes during the postsaccadic fixation period.