latent nystagmus

Latent nystagmus is a horizontal jerk nystagmus that appears on covering one eye and is absent with both eyes open.^1,2 The fast phase beats toward the uncovered, fixating eye and the slow phase drifts toward the covered eye, and covering the other eye reverses the direction.^1,2 Both eyes develop the nystagmus, and the fixating eye drifts nasally and corrects with a temporal fast phase.³

Latent nystagmus is associated with infantile esotropia and dissociated vertical deviation.¹ The condition, also called fusion maldevelopment nystagmus syndrome, is thought to arise from unequal visual input to the two eyes.³ One proposed mechanism is a failure to suppress a nasally directed subcortical optokinetic bias as a result of impaired cortical binocular vision.³ The amplitude increases in abduction and decreases in adduction, and the slow phase has a decreasing velocity, unlike the increasing-velocity slow phase of manifest congenital nystagmus.^3,4

True latent nystagmus is rare, and most patients have a low-intensity nystagmus with both eyes open that increases on occlusion, called manifest-latent nystagmus.^1,2 The nystagmus may also become manifest without occlusion if one eye has poor vision or is suppressed, as with strabismus, cataract, uncorrected refractive error, or amblyopia.^2,3 Vision with both eyes open may be much better than monocular acuity, and monocular acuity can be measured by fogging the fellow eye with high plus lenses, with polarizing lenses, or with the red-green duochrome slide.³