What is Dissociated Vertical Deviation?
“Dissociated vertical deviation” or DVD, is a term introduced by Bielschowsky. It also goes by many other names like “alternating hyperphoria,” “double hyperphoria,” “occlusion hyperphoria,” and so on. Simply put, DVD is where one eye moves vertically while the other eye stays focused on a target. It generally happens in both eyes but is not always equally noticeable.
DVD typically appears when something disrupts the way the eyes work together, whether that’s due to a physical issue, a sight problem, or a sensory interference. The DVD condition consists of three parts: hyper deviation, abduction, and excyclotorsion. These signs may show up when a person is tired or daydreaming or may only appear during specific eye tests. An intriguing observation is that when the deviated eye shifts downwards to focus, the other eye doesn’t move correspondingly – this actually goes against what’s known as Herring’s law.
What Causes Dissociated Vertical Deviation?
The cause of dissociated vertical deviation, a type of eye disorder, is still unknown. However, there are a few key things that researchers think might contribute:
1. There might be an imbalance in the strength of the eye muscles that move the eye up and down. This can disturb the signal sent from each balance organ in the inner ear.
2. There could be issues with the pathway that carries visual signals from the eye to the brain.
3. Lastly, there might be an imbalance of stimulation between the two eyes.
Risk Factors and Frequency for Dissociated Vertical Deviation
In the US, between 3% to 5% of kids have a condition called strabismus. This is a condition where the eyes don’t line up in the same direction. Of these cases, 1.9% have been seen to show a special kind of strabismus called dissociated vertical deviation (DVD). This is more commonly related to sensory esotropia (where the eye turns inward) rather than exotropia (where the eye turns outward).
According to some studies, DVD was found in 12.5% of patients with another type of strabismus called sensory hypertropia. Furthermore, among the different kinds of strabismus related to DVD, the most common were:
- Congenital esotropia (a kind of eye misalignment present at birth) seen in 53% of the cases
- Esotropia with a developmental deficit (an inward turning of the eyes developing during childhood), in 25% of the cases, and
- Accommodative esotropia (related to difficulty in focusing the eyes) in 3.4% of the cases.
Signs and Symptoms of Dissociated Vertical Deviation
Dissociated vertical deviation (DVD) is an eye condition that usually occurs in young kids between 2 to 5 years old. DVD could happen on its own or it could be found alongside other eye problems, like infantile esotropia, which is the most common, or less common ones like infantile exotropia, or Duane’s retraction syndrome. DVD is usually seen in both eyes, but not always to the same degree. It tends to be more prominent in the eye with poorer vision (amblyopic eye).
The symptoms of DVD can be grouped into the following categories:
- Deviation: This is when the non-fixating eye (the eye not focused on an object) drifts upward when the other eye is fixating on a target. This drifting eye often shows a tendency to rotate outward and display a slight outward movement. The other eye remains still as it concentrates on the object. This symptom contradicts the normal alignment of the eyes.
- Head Posture: Sometimes, about one-third of patients with DVD tilt their heads in an unusual manner. This is a way for them to retain single and clear vision. Generally, they don’t experience double vision and their vision is good in both eyes.
- Sensory Adaptations: While patients usually have good binocular vision (using both eyes to see), this becomes difficult when one eye deviates. The brain spontaneously suppresses the image from the misaligned eye to avoid double vision.
DVD can be subgrouped in various ways when it comes to type and degree:
- Type by Alignment Changes:
- Comitant: The vertical deviation, or the misalignment, is the same whether the eyes look to the side, straight ahead, or towards the nose.
- Incomitant: The vertical deviation varies depending on whether the eyes look to the side, straight ahead, or towards the nose.
- Type by Degrees of Deviation: This is measured via the angle of deviation, represented in prism diopters (PD).
- Mild: 0 to 9 PD
- Moderate: 10 to 19 PD
- Severe: More than 20 PD
Testing for Dissociated Vertical Deviation
Diagnosing a condition known as dissociated vertical deviation (DVD) involves a clinical examination using several critical tests.
Firstly, a doctor might use Spielmann’s translucent occluder in the Cover/Uncover Test. If there’s a manifest DVD, the deviated eye will exhibit a downward shift once the fixating eye is covered. For latent DVD, the deviation only becomes noticeable once the eyes are dissociated. In this case, the uncovered eye remains stationary, while the covered eye elevates and then lowers once it’s uncovered.
Another test is the Head tilt test, where the deviation or shift of the eye tends to increase when a person tilts their head to the side.
The Bielschowsky’s graded density filter test is then performed. This test involves covering one eye and placing a bar containing increasingly denser filters in front of the fixing eye. As progressively denser filters are placed over the fixating eye, the elevated and covered eye begins to lower. As filters of lesser density are placed in front of the fixating eye, the other eye underneath the cover starts elevating again.
During the Red filter test, a dissociation test, a red glass is placed in front of one eye, which makes the eye behind the glass filter drift up. This test helps differentiate DVD from other eye deviations, as the position of a red light relative to a fixation light won’t change regardless of which eye is doing the fixating.
The measurement of DVD is done using a base-down prism. A prism is placed in front of the deviated eye, and the patient is asked to focus on a distant target. The cover is then shifted to the fixating eye, allowing the deviating eye to take over. This process is repeated with more potent prisms until there’s no more downward movement in the deviated eye. In patients with DVDs in both eyes, this test is repeated for each eye separately.
In grading DVD, +1 deviation indicates a slight deviation, +2 a small deviation, +3 a moderate deviation, and +4 a significant deviation.
Treatment Options for Dissociated Vertical Deviation
The treatment method for a condition known as dissociated vertical deviation (DVD) can range from simply monitoring the condition, to non-invasive treatments, or even surgical interventions.
1. Monitoring, or “observation”, can work for certain patients. This is often enough for older patients who are eight years or above since vision impairment (amblyopia) is less of a worry, or when the person only exhibits slight abnormal head postures and no worrisome cosmetic changes.
2. Non-surgical treatments may work for minor manifestations of DVD. This typically involves altering the patient’s focusing habits or encouraging eye coordination. One effective strategy is to induce a slight visual distortion in the dominant eye — by introducing a +2D lens, for instance. This technique makes the other eye take over the dominant role, which helps prevent DVD. Also, injecting a substance known as Botulinum toxin into a strong eye muscle has also been found beneficial.
When the case is more severe — such as if the patient has a deviation of +2 or more, frequent DVD symptoms, abnormal head posture, or major cosmetic issues— surgery is usually needed. There are several surgical procedures, some of which are: weakening of the inferior oblique muscle; moving the inferior oblique muscle forward; combining forward movement with trimming of the muscle; significant reduction of the superior rectus muscle (around 7 to 10 mm); or the Faden operation paired with a smaller (3 to 5 mm) reduction of the superior rectus muscle.
Cutting or tucking the inferior muscle can also work, especially in certain case-specific scenarios. For smaller deviations, a 4 mm cut is sufficient, a 6 mm cut helps with average deviations, and an 8 mm cut is needed for large deviations. In some instances, the transposition of the inferior oblique to the anteronasal area or a surgery on all four oblique muscles can be performed.
The choice of surgery is usually determined by the level of DVD and the existence of inferior oblique overaction (IO). For example, if the DVD is absent of IO overaction, the surgery will focus on the recession of the superior rectus muscle and the cutting of the inferior rectus muscle. Cases with moderate DVD and IO overaction typically require the repositioning and recession of IO. Severe cases, with corresponding IO overaction, may necessitate both the repositioning and recession of the inferior oblique muscle as well as the significant reduction of the superior rectus muscle (7 to 10mm).
What else can Dissociated Vertical Deviation be?
When trying to diagnose Dissociated Vertical Deviation (DVD), doctors must consider similar conditions. Two major conditions they have to rule out are a muscle overactivity condition known as Inferior Oblique Overaction (IOOA) and a condition known as acquired skew deviations. The correct diagnosis is important because the treatment methods for these conditions are different.
There are some key differences to help distinguish between IOOA and DVD:
- When a patient has IOOA, their upward eye movement is most extreme when the eye turns inward. In DVD, the intensity of the eye movement is nearly the same no matter if the eye looks straight, inward or outward.
- A “V” pattern eye movement is linked to IOOA, but usually it does not occur in DVD patients.
- IOOA often comes with too little activity in your superior oblique, a muscle above the eye.
- In IOOA patients, you can find a tilted macula, which is a part in the back of your eye. This is usually not present in DVD patients.
- People with DVD can experience a phenomenon where their eyes turn when their head is tilted. This doesn’t happen in IOOA
The key points to distinguish between acquired skew deviation and DVD include:
- Acquired skew deviations can occur at any age, while the typical age for DVD to appear is between 2-4 years.
- In acquired skew deviations, the higher eye inwardly rotates and the lower eye outwardly rotates, whereas the opposite happens in DVD.
- Acquired skew deviation can happen together with damage to the brainstem or cerebellar region.
- Patients with skew deviation may experience double vision lined up vertically, which isn’t common in DVD.
- Acquired skew deviation patients might also experience a form of nystagmus, a vision condition in which the eyes make repetitive, uncontrolled movements. This is not common with DVD, which is usually accompanied by a different form of nystagmus.
What to expect with Dissociated Vertical Deviation
The treatment for dissociated vertical deviation, a condition that causes the eyes to stray up and down, can vary. The approach depends on the severity of the condition and how often it occurs. It can be observed without immediate treatment or might require non-surgical or surgical techniques. There’s no substantial research comparing the effectiveness of non-surgical versus surgical treatment options.
Commonly performed surgical treatments include two procedures: weakening the superior rectus muscle (a muscle controlling eye movement) or moving the inferior oblique muscle towards the front of the eye. The choice of procedure depends on the severity of the patient’s eye deviation, the degree of any abnormal head postures as a result of the deviation, and the surgeon’s preference.
Possible Complications When Diagnosed with Dissociated Vertical Deviation
There are various types of complications that can occur after surgery. These can be due to the disease itself, as a result of anesthesia, or from the surgery (occurring either during or after the operation).
- Disease-related complications include amblyopia (lazy eye), torticollis (twisted neck), and sternocleidomastoid muscle contracture (tightening of the neck muscle).
- Anesthesia-related complications can include the Oculocardiac reflex (a decrease in pulse rate caused by pressure on the eye), malignant hyperthermia (a potentially fatal reaction to certain drugs used during anesthesia), cardiac arrest, liver disease (hepatic porphyria), or breathing problems caused by succinylcholine (succinylcholine-induced apnoea).
- Surgical complications could be:
- Intraoperative (during surgery) – bleeding (hemorrhage), loss or slippage of a muscle, eyeball damage (perforation), unintended injury to surrounding structures or muscles, or operating on the wrong muscle or eye.
- Postoperative (after surgery) – surgical suture reactions, growth of tiny granulation tissue (conjunctival granuloma), anterior ischemia (insufficient blood flow to the front of the eye), double vision (diplopia), detached retina, under- or overcorrected vision problems, or adhesive syndrome (scarring).
Recovery from Dissociated Vertical Deviation
After surgery, the patient should be given low-dose topical steroids, specifically 0.5% loteprednol, four times daily for a week, which should then be gradually decreased. At the same time, topical antibiotics, specifically 0.5% moxifloxacin, should be used four times a day for 20 days. To ease the pain, oral pain relievers, like 50 mg diclofenac, can be taken twice a day for the first 3 to 5 days. The patient should return for a check-up after a month to assess their head position and eye deviation.
The patient and their parents need to understand the significance of regular check-ups and sticking with their medication regimen. To prevent lazy eye development, the parents should be aware of the need for eye patching or occlusion therapy if there’s remaining eye deviation. This is particularly important for children under 8 years old. The patient should return for follow-up visits every three months and twice a year thereafter, until they’ve passed the age where lazy eye is most likely to develop.
Preventing Dissociated Vertical Deviation
It’s crucial to involve patients and their parents or guardians in medical decisions related to their care. For children showing only slight symptoms, simple monitoring or patching the affected area could be sufficient – as long as they have regular check-ups. Parents need to be reassured and educated about the usual progression of their child’s condition.
If surgery becomes necessary, it’s essential to have a detailed conversation with the parents about the potential benefits and risks. They should also be made aware of the possible psychological effects that strabismus, or being cross-eyed, may have on their child. Directing them to support groups could greatly benefit their child’s overall wellbeing and recovery process.
