Horizontal saccadic velocities in Duane's syndrome.

Horizontal ocular saccadic velocities were measured by electro-oculography in 33 patients with Duane's syndrome. In 28 patients with limited abduction associated with retraction on adduction (Type 1), abduction saccadic velocity was markedly reduced while adduct-on saccades were moderately slow. In three patients with exotropia and good abduction but associated limited adduction and retraction on adduction (Type 2), abduction velocity was good, while adduction saccadic speed was slow. In two patients with limited abduction and adduction with retraction on adduction (Type 3), abduction and adduction saccadic velocity was appreciably slow. Ocular electromyographic testing selected patients indicated that slow abduction saccades could be explained by absence of lateral rectus muscle recruitment, while slow adduction saccadic speed could be explained by paradoxical innervation of the lateral rectus muscle.