Compensatory mechanisms in congenital nystagmus.

Congenital nystagmus may occur in a manifest or latent form. Since most patients with latent nystagmus also have nystagmus with both eyes open (manifest latent nystagmus), differentiation between these two entities frequently requires electronystagmographic wave form analysis. Such analysis shows distinctive characteristics for manifest and latent or manifest latent congenital nystagmus, suggesting different origins. Several compensation mechanisms exist by which congenital nystagmus is decreased and visual acuity improved. For manifest nystagmus, these mechanisms include version or convergence innervation or a rest point between primary position and maximal lateroversion. In latent or manifest latent nystagmus, the nystagmus decreases when the fixating eye is adducted. Patients with manifest congenital nystagmus may use several of these compensation strategies. Because of the difficulties involved in distinguishing between manifest and manifest latent nystagmus without electronystagmography, confusion has arisen regarding the etiologic relationship between congenital nystagmus and infantile esotropia. Such relationship clearly exists in some patients with manifest nystagmus and convergence dampening. However, in most patients with infantile esotropia and congenital nystagmus, the nystagmus is latent or manifest latent and there is no evidence of a causal relationship between these two entities.