Dissociated vertical deviation (DVD) is an eye condition which occurs in association with a squint, typically

infantile esotropia Infantile esotropia is an ocular condition of early onset in which one or either eye turns inward. It is a specific sub-type of esotropia and has been a subject of much debate amongst ophthalmologists with regard to its naming, diagnostic features ...

. The exact cause is unknown, although it is logical to assume it is from faulty innervation of eye muscles.

Presentation

The eye drifts upward spontaneously or after being covered. The condition usually affects both eyes, but can occur unilaterally or asymmetrically. It is often associated with latent or manifest-latent

nystagmus Nystagmus is a condition of involuntary (or voluntary, in some cases) eye movement. Infants can be born with it but more commonly acquire it in infancy or later in life. In many cases it may result in reduced or limited vision. Due to the invol ...

and, as well as occurring with

, can also be found associated with

exotropia Exotropia is a form of strabismus where the eyes are deviated outward. It is the opposite of esotropia and usually involves more severe axis deviation than exophoria. People with exotropia often experience crossed diplopia. Intermittent exotrop ...

s and vertical deviations. DVDs are usually controlled from occurring with both eyes open, but may become manifest with inattention. 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. The level of dissociative occlusion required may involve using a red filter, a darker filter or complete occlusion (e.g. with a hand).

Onset

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.

Mechanism

Dissociation refers to the situation where the innervation of one eye causes it to move involuntarily and independently of the other eye. Usually both eyes work together as described by Hering's and Sherrington's laws of innervation. A DVD is a slow upward and sometimes temporal movement of one eye, with cortical

suppression Suppression may refer to: Laws * Suppression of Communism Act *Suppression order a type of censorship where a court rules that certain information cannot be published * Tohunga Suppression Act 1907, an Act of the Parliament of New Zealand aimed ...

of the vision in that eye while it is deviated. 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 Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amb ...

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 The superior rectus muscle is a muscle in the orbit. It is one of the extraocular muscles. It is innervated by the superior division of the oculomotor nerve (III). In the primary position (looking straight ahead), its primary function is elevat ...

or anterior transposition of the

inferior oblique muscle The inferior oblique muscle or obliquus oculi inferior is a thin, narrow muscle placed near the anterior margin of the floor of the orbit. The inferior oblique is one of the extraocular muscles, and is attached to the maxillary bone (origin) an ...

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.

References

{{reflist, refs {{cite book, author=F Rowe, title=Clinical Orthoptics, publisher=Blackwell, edition=2nd, year=2004 Eye diseases