Visual acuity and motor characteristics in congenital nystagmus.

Improvement in visual acuity at near fixation in patients with congenital nystagmus has been explained on the basis of nystagmus damping, caused by superimposed convergence innervation. However, an electronystagmographic study of 13 patients with congenital nystagmus and improvement in visual acuity at near fixation failed to show a consistent decrease of nystagmus intensity at near fixation. Visual acuity at near fixation improved regardless of whether the nystagmus intensity decreased or increased. Factors other than nystagmus amplitude or frequency may be modified by convergence innervation and cause an increase in visual acuity at near in patients with congenital nystagmus.