A hypothetical mechanism for DVD: unbalanced cortical input to subcortical pathways.

Dissociated vertical divergence (DVD) is commonly encountered in the infantile strabismus syndrome. The movement is said to be dissociated since alignment differs between right and left eye fixation. It has been hypothesized that DVD is caused by a primitive reflex present in fish. Visual pathways in the fish brain indeed are dissociated with complete crossing at the optic chiasm and projection to the superior colliculus instead of a visual cortex. Neuroanatomical data and clinical characteristics of DVD, however, contradict this hypothesis. From these data a new hypothesis arises: corticotectal lateralization. The absence of binocular development in the cerebral cortex in infantile strabismus gives rise to dissociated activation of subcortical pathways through individual less tightly linked colliculi.