Dissociated Vertical Deviation
Encyclopedia
Dissociated Vertical Deviation (DVD
) is an ocular condition which occurs in association with a squint, typically Infantile Esotropia
.
and Sherrington's
laws of innervation. A DVD is a slow upward and sometimes temporal movement of one eye, with cortical suppression
of the 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).
, can also be found associated with exotropia
s and vertical deviations.
DVD's 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).
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 is observed NOT of the eye beneath the filter. 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.
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
) is an ocular condition which occurs in association with a squint, typically Infantile Esotropia
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, and treatment.- Name and features :Historically...
.
Mechanism
Dissociation refers to the situation where the innervation of this eye movement occurs involuntarily and independently of the other eye. Usually both eyes work together as described by Hering'sHering's law of equal innervation
Hering's law of equal innervation is used to explain the conjugacy of saccadic eye movement in stereoptic animals. The law proposes that conjugacy of saccades is due to innate connections in which the eye muscles responsible for each eye's movements are innervated equally...
and Sherrington's
Sherrington's law of reciprocal innervation
Sherrington's law of reciprocal innervation, also called Sherrington's law II explains how a muscle will relax when its opposite muscle is activated. René Descartes had hypothesized as much in 1626...
laws of innervation. A DVD is a slow upward and sometimes temporal movement of one eye, with cortical suppression
Suppression (eye)
Suppression of an eye is a subconscious adaptation by a person's brain to eliminate the symptoms of disorders of binocular vision such as strabismus, convergence insufficiency and aniseikonia. The brain can eliminate double vision by ignoring the images of one of the eyes...
of the 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).
Characteristics
The condition usually affects both eyes, but can occur unilaterally or asymmetrically. It is often associated with latent or manifest-latent nystagmus and, as well as occurring with Infantile esotropiaInfantile 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, and treatment.- Name and features :Historically...
, can also be found associated with exotropia
Exotropia
Exotropia is a form of strabismus where the eyes are deviated outward. It is the opposite of esotropia. People with exotropia often experience crossed diplopia. Intermittent exotropia is a fairly common condition. "Sensory exotropia" occurs in the presence of poor vision...
s and vertical deviations.
DVD's 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).
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.Testing for DVD
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 is observed NOT of the eye beneath the filter. 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.