Dissociated vertical deviation (DVD) is an eye condition which occurs in association with a squint, typically infantile esotropia.
The exact cause is unknown, although it is logical to assume it is from faulty innervation of eye muscles.
Usually some level of dissociative occlusion is required to trigger the brain to suppress vision in that eye and then not control a DVD from occurring.
DVD typically becomes apparent between 18 months and three years of age; however, the difficulties of achieving the prolonged occlusion required for accurate detection in the very young make it possible that onset is generally earlier than these figures suggest.
DVD can be revealed on ocular movement testing when one eye is occluded by the nose on lateral gaze.