All about Dissociated Vertical Deviation (DVD) in Eyes »
By Aastha Subedi & Jenisha Bhattarai
Introduction to DVD
Dissociated vertical deviation (DVD) is one of the ill-understood forms of strabismus. In this article, we will be talking about an introduction to DVD, along with clinical features, differential diagnosis, and management or treatment of dissociated vertical deviation.
Before diving into the dissociated form of vertical deviation let’s spend some time learning about vertical deviations.
Like horizontal deviation, the vertical deviation can be either comitant or incomitant. It might be congenital or acquired and can be expressed in the form of hyperphoria, intermittent hypertropia, or constant hypertropia.
Based on the involved eye, vertical deviation may be left or right hypertropia. Similarly, it occurs solely or in association with horizontal deviation.
Vertical deviation has been found to occur in approximately 5 percent of squints. Most of the vertical deviations are incomitant in nature.
Types of vertical deviations
Comitant vertical deviations
In comitant deviation, the amount of deviation in the squinting eye remains constant (unaltered) in all the directions of gaze with no ocular movement limitation.
It is of two types, hypertropia, and hypotropia. Intermittent deviations are more common than the constant form of deviation. Suppression, Amblyopia, or Vertical abnormal retinal correspondence (ARC) may occur in comitant vertical deviation.
Incomitant vertical deviaitons
Here, amount of deviation varies in different directions of gaze. Different types of incomitant vertical deviations are apparent oblique muscle dysfunction (A, V, X, Y pattern), paretic vertical deviation, and restrictive vertical deviation. The patient may acquire nnomalous head posture (AHP).
Dissociated Vertical Deviation (DVD) in Eyes
As mentioned earlier, the dissociated vertical deviation is a comparatively ill-understood form of strabismus. It is basically a bilateral (also unilateral) anomaly characterized by hyper deviation of either eye when the other eye is fixating. Hyperdeviation is accompanied by extortion & slight exodeviation.
If the fixing eye is covered, the squinting eye takes fixation by moving down along with intortion. It does not obey Hering’s law of ocular movement because just covered fixing eye does not make any movement. Hence, the term ‘dissociated’ is used.
Simply, DVD is characterized as an upward deviation of one eye or alternately of both eyes, which occurs either spontaneously or in testing situations when one eye is occluded. The deviation may be latent or manifest but is always intermittent.
Beilschowsky coined the term ‘Dissociated Vertical Deviation’ in 1931 AD. Likewise, Stevens first described DVD as ‘Double Vertical Strabismus’. Later on, Lanchester & Swan introduced the term ‘Alternating sursumduction’ that emphasizes the monocular nature of the movement (duction & not a vergence or version).
Synonyms (Other Names)of Dissociated Vertical Deviation
DVD is reflected by many terms used at one time or the other.
- Anatropia, Anaphoria
- Alternating hypertropia, hyperphoria
- Alternating sursumduction
- Double hypertropia
- Occlusion hypertropia, hyperphoria
- Dissociated double hypertropia
- Dissociated alternating hyperphoria
- Dissociated vertical divergence
- Alternating vertical deviation
- Dissociated hyperphoria, hypertropia
- Periodic vertical squint
- Presumptive hyperphoria
Controversy regarding the terminology of DVD
The dissociated vertical deviation is different from normal hyper deviation as both eyes are elevated when covered. In right hypertropia (RHT), either the right eye is elevated when the left is fixating or the left eye is depressed when the right is fixating. In DVD, either eye elevates when fellow eye is fixating.
Similarly, alternating sursumduction emphasizes the monocular nature of the movement (i.e., duction not version, or vergence). The term “sursumduction” is not completely accurate as movements in DVD are not restricted to sursumduction exclusively, excycloduction and abduction also accompany.
Deviation doesn’t always alternate but may be restricted to one eye. The term ‘Dissociated Vertical deviation’ is most preferred as two eyes are independent of each other (dissociated movements).
Dissociated deviation syndrome includes excycloduction, abduction, and latent nystagmus. Dissociated deviation in the upward movement of eyes is called dissociated vertical deviation, and in excyclotorsion in known as dissociated torsional deviation. Similarly, the dissociated deviation in lateral movement of the eyes is termed as dissociated horizontal deviation.
Types of dissociated vertical deviation (DVD)
The dissociated vertical deviation is classified as a comitant DVD and incomitant DVD.
- Comitant dissociated vertical deviation: Vertical deviation, usually (within ± 7 PD) measures the same in abduction, primary position, and adduction.
- Incomitant DVD: Difference in the magnitude of deviation in abduction, primary position, and adduction.
Clinical Features of Dissociated Vertical Deviation
On the basis of deviation, DVDs are of four types: unilateral, bilateral, manifest, and latent.
- Unilateral DVD
It is characterized by the occurrence of vertical deviation in one eye while no movement in other eyes.
- Bilateral DVD
In patients with alternate or bilateral DVDs, either eye elevates under cover (double hyper deviation) while the uncovered eye moves down to take fixation.
- Manifest DVD
It is noticed when the patient is fatigued or daydreaming.
- Latent DVD
In patients with latent DVD, there occurs no movement of the uncovered eye, but the eye under cover is elevated & moves downward after it is uncovered (i.e DVD is present only when the eyes have been dissociated)
In dissociated vertical deviation, there is slow upward drifting of a non-fixing eye when occluded or spontaneously during periods of in-attention & downward movement of the eye when the occlusion is removed or when a refixation stimulus occurs. The vertically deviated eye is also extorted & slightly abducted.
The amount of elevation when the eye is covered is variable, tending to increase after prolonged occlusion, often differing between two eyes. Similar but not precisely equal amounts of sursumduction for a given eye in primary position, abduction, or adduction.
The dissociated vertical deviation is present in over 75% of cases of essential infantile esotropia. Most of them become evident after surgical alignment for horizontal squint. There is a common association of DVD with infantile exotropia; as high as 90% (Lang J: Congenital strabismus,1972), and heterotropia of sensory origin.
DVD may occur as a part of a syndrome consisting of an A- pattern exotropia with overaction of superior obliques and underaction of inferior obliques. Similarly, Latent nystagmus with cyclovertical components may be associated with dissociated vertical deviation.
DVD may occur as an isolated phenomenon in patients with apparently normal binocular function. Likewise, excycloduction and latent nystagmus are frequently associated with DVD. No specific hereditary basis is noted.
III. Head posture
Approximately, one in three patients with DVD has a spontaneous abnormal head posture (Anderson et.al, 1959). Mostly head found to be tilted towards the same side of the eye with a larger vertical deviation. Tilting towards opposite side increases vertical deviation. Likewise, chin depression is reported in patients with bilateral DVDs (De Decker,1999).
- Bielschowsky phenomenon
The elevated eye behind cover makes gradual downward movement and even move below the primary position when visual input to the fixating eye is progressively decreased by photometric neutral filter wedge.
The dissociated vertical deviation is usually bilateral and asymmetrical. (14% unilateral, 9% symmetrical; Von Norden, 1998). Unilateral occurrence is often observed in deeply amblyopic eyes (Beilschowsky et.al, 1931) and in sensory heterotropia (Romero et.al, 1980).
Asymmetry in two eyes is reversed in the supine position and head tilted back. (Goltz et.al, 1996). This suggests a possible effect of inputs from otolithic & possibly neck muscle sensors on the amplitude of DVD.
Monocular dissociated hyperdeviation may be seen in the presence of intermittent exotropia (IXT). On disruption of fusion, deviated eye is elevated & not associated with underaction of yolk muscles.
In bilateral DVD (Alternating sursumduction or double hyperdeviation), either eye elevates and extorts under cover. There is no corresponding hypotropia of the fellow eye, i.e DVD doesn’t follow Hering’s law.
- Binocular vision & sensory adaptation
Suppression usually develops in a person with spontaneous DVD and thus eliminates diplopia. However, binocular vertical perceptional adaptations are also reported (Campos et.al, 1998).
Peripheral fusion is often present in DVD having a manifest deviation of 4 prism D or less. An absolute central scotoma in one eye, while both eyes are being used for peripheral fusion is present even in latent dissociated vertical deviation.
VII. Red glass test
In the red glass test patient will localize the red image below the fixation light, regardless of whether the red glass is held before the right or left eye.
VIII. Measurement of Dissociation Vertical Deviation
First of all, Visual Acuity should be sufficient enough to visualize the fixation target. As the patient fixates 6m or 33cm distance, the occluder is quickly shifted to the fixating eye, allowing previously dissociated elevated eye to take up fixation.
An alternate cover test is done, increasing amount of base down prisms are held under the occluder in front of non- fixating eye until the downward fixation movement of that eye is neutralized.
The prism cover test (PCT) should be done separately before each eye in case of bilateral DVD as mostly DVD is asymmetrical.
Modified Krimsky test may be used to measure DVD in patients who can’t fix with deviating eyes. Here, an increasing amount of base down prism is placed before deviating eye until corneal reflex is centered in the deviating eye.
Appropriate grading of dissociated vertical deviation may be done on a cover test as follows:-
- 1+ deviation= a slight deviation
- 2+ deviation= a small deviation
- 3+ deviation= a moderate deviation
- 4+ deviation= a large deviation
For grading, the occluder should be turned obliquely so that the eye remains occluded and the examiner can look behind the occluder.
Reasons behind difficulty to quantify DVD
It is difficult to quantify the dissociated vertical deviation because the deviation tends to be variable and without clear endpoints, making prism and cover measurements difficult and unreliable. Similarly, nystagmus, both horizontal and rotary, is frequently present, although it may be difficult to appreciate because amplitudes may be small and the frequency rapid.
Dissociation and corrective movements are slow and variable in speed and usually associated with other strabismus.
Differential Diagnosis of DVD in Eyes
Diagnosis of DVD
It is easier to see DVD when a patient fixates a distance target because DVD is greater at distance. Here, either eye elevates when fellow eye is fixating. The elevation is followed by extorsion and refixation is followed by intorsion. The vertical angle of dissociated deviation is somewhat less in abduction than in adduction.
Similarly, latent nystagmus occurs in approximately half the patients with DVD. It is often found in association with infantile esotropia and less often with accommodative acquired esotropia, exotropia, and heterotropia of sensory origin. Head tilt is seen towards fixating eye. DVD is likely to develop poor BSV.
DVD Versus Overaction of Inferior Oblique Muscle
In DVD, the covered eye becomes elevated in abduction, primary position, and adduction. Conversely, with the overaction of IO muscles, each eye becomes elevated primarily in adduction but never in abduction unless there is coexisting contracture of ipsilateral superior rectus (SR) muscle.
When a patient with overacting IO muscle fixates with the involved eye in the field of action (elevation and adduction) the contralateral SR will underact. Conversely in patients with DVD who are tested in the same manner under the action of contralateral yoke muscle doesn’t occur.
Refixation movement in overaction of IO is rapid, about 20 to 400°/s. But refixation movement is slow in dissociated vertical deviation is 10 to 200°/s. Tonic incycloduction in IO overaction when takes refixation is so rapid that it cannot be appreciated. While in DVD excyclotorsion on elevation and on refixation intorsion can easily be observed.
Both A and V patterns can be seen in DVD, however, A patterns are more common and this can differentiate DVD from IO overaction where V patterns would be expected.
Latent nystagmus is usually present in DVD but absent in IO over action. Likewise, the Bielchowsky darkening wedge test is positive in DVD and negative in IO over action.
Bielchowsky darkening wedge test
The principle behind the Bielchowsky darkening wedge test is to gradually reduce the amount of light entering the eye. A graded wedge was originally used but a neutral filter density bar is preferred nowadays. The patient fixates a light and the non-fixating eye is occluded, hence the eye behind the occluder will elevate.
As the density of the neutral filter is gradually increased before the fixating eye, the eye under cover will be seen to move down possibly below the midline. As the filter density is reduced the eye under cover will progressively elevate again.
Red glass test
Red glass yields peculiar results in dissociated vertical deviation. Regardless of whether the red filter is placed before the right or left eye the patient describes a red image below a white image. This contrasts with patients with a true vertical deviation. In true hypertropia the second (red) image is seen above or below the primary image depending on whether the red filter is placed before hypo or hyper deviated eyes.
DVD and superior Oblique (SO) overaction
The SO muscles formerly were implicated as a possible cause of DVD. However, the report of A pattern exotropia, SO overaction, and DVD made this hypothesis unpopular. Recent studies have resurrected this theory based on the fact that the eye elevates and undergoes excyclotorsion in DVD. A hypo-functioning SO muscle could explain both findings.
Management or Treatment of Dissociated Vertical Deviation
The initial management consideration for a patient with DVD is the prognosis for establishing a normal binocular vision. If the prognosis for establishing BSV is good, the management strategy is based on the characteristics of associated horizontal strabismus. If the prognosis is poor, the treatment is directed towards addressing concerns about cosmesis.
The sequential Strategy
Its general treatment strategy is to avoid those viewing conditions that produce temporary abnormal innervations and to enhance those conditions that prevent the manifestation of DVD. The sequential strategy includes:
- Prescribe the appropriate lens correction for far and near
- Determine the dissociated horizontal and vertical deviations at far and at near (Note which eye has larger hyperdeviations).
- Prescribe associated viewing Active Vision Therapy to establish peripheral sensory fusion without a vertical prism or prism target separation (Avoid dissociation and darkening of eyes).
- Prescribe minimum vertical prism resulting in stable sensory fusion if primary component.
- Prescribe AVT to improve motor fusion range. Note the vertical need for sensory fusion if a primary component is present.
- Prescribe the vertical prism or the most frequently encountered vertical prisms that results in stable central sensory fusion at the ortho position.
- Establish efficient binocular vision in open space at all distances.
Prisms should not be given until such time that a primary component is identified. Measuring the objective angle under associated viewing conditions (eg. Major amblyoscope) can give more reliable results.
Occlusion may be needed to eliminate sensory anomalies such as suppression, amblyopia, and abnormal retinal correspondence (ARC). (Note – Covering one eye may result in larger and more variable hyperdeviations when the patch is removed)
Active Vision Therapy
In orthoptics, procedures for constant strabismus DVDs are best approached by first ignoring the vertical condition. Anti-suppression procedures are prescribed with the goal to achieve normal sensory fusion. Some DVD patients progress to the efficient binocular vision showing no vertical deviation when associated. While some may show an accompanying primary vertical requiring prism therapy to maintain efficient binocular fusion.
Surgical procedures preferred by various authors are:
- The recession of superior combined with resection of the inferior rectus muscle.
- Resection of inferior recti
- Retroequatorial myopexy (posterior fixation) of superior recti combined with or without a recession of these muscles.
- Unconventionally large recessions (5 to 10 mm) of superior recti.
- Anterior displacement of inferior oblique insertion which may be combined with superior rectus recession.
The overaction of the inferior oblique (IO) may look like dissociated vertical deviation or vice versa. So meticulous observation or other tests (if required) are performed to make the diagnosis. DVD should not be chased with vertical prisms. Likewise, the key in the management of DVD is to establish normal sensory fusion first. After sensory fusion occurs the presence of a primary vertical component either comitant or non comitant is often clearly evidenced.
DVD Powerpoint Presentation (PPT & PDF)
PPT of Dissociated Vertical Deviation (DVD)
About the Authors
Aastha Subedi & Jenisha Bhattarai are Clinical Optometrists (IOM, Nepal).