On returning downward and possibly inward to take up fixation, the DVD slow movement will be reversed. The dissociative movement seen objectively should not be confused with the dissociation that occurs subjectively - as when the brain begins to not visualise both images simultaneously (by ignoring or suppressing vision in that eye). Diagnosis
A test called the Bielschowsky Darkening Wedge Test can be used to reveal and diagnose the presence of dissociated vertical deviation, although any (or no) amount of dissociative occlusion may also prompt it to occur. The patient is asked to look at a light. One eye is covered and a filter is placed in front of the other eye. The density or opacity of this filter is gradually increased, and the behaviour of the eye under the cover (not of the eye beneath the filter) is observed. Initially, if DVD is present, the covered eye will have elevated, but as the filter opacity is increased the eye under the cover will gradually move downwards. This Bielschowsky phenomenon is present in over 50% of persons with prominent DVD, all the more if the DVD is asymmetric and amblyopia is present as well.The Bielschowsky phenomenon is also present in the horizontal plane in patients with prominent DHD (dissociated horizontal deviation). Differential diagnosis
DVD is often mistaken for over-action of the inferior oblique extra-ocular muscles. DVD can be revealed on ocular movement testing when one eye is occluded by the nose on lateral gaze. This eye will then elevate, simulating an inferior oblique over action.
However, in a unilateral case, overaction of the superior rectus muscle in the unaffected dominant eye, can also be a causing factor as well as causing a V pattern exophoria. Treatment
Management of this condition is surgical and typically involves reducing the strength of the superior rectus muscle or anterior transposition of the inferior oblique muscle of the affected eyes.Several different surgical procedures exist for the correction of DVD including: inferior oblique anteriorization, inferior oblique anteriorization plus resection, superior rectus recession, superior rectus recession plus posterior fixation suture, and inferior oblique myectomy, though there is insufficient evidence to determine which procedure results in the best outcomes for patients. See also
Strabismus
Strabismus surgery
Pediatric ophthalmology
Infantile esotropia


== References ==