Ординатура / Офтальмология / Английские материалы / Handbook of Pediatric Strabismus and Amblyopia_Wright, Spiegel, Thompson_2006

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A- and V-Pattern Subtypes

Look critically at the type of pattern: is it symmetrical or does the change in horizontal deviation occur more in upgaze or downgaze? This is important to know, as the configuration or subtype of the A- or V-pattern can indicate an identifying etiology and can influence the surgical plan. For example, a V-pattern consisting of convergence in downgaze without significant change in horizontal deviation from primary position to upgaze is highly suggestive of a bilateral superior oblique palsy. Listed below are subtypes of A- and V-patterns in which the change in horizontal deviation is asymmetrical.

V-PATTERN SUBTYPES

Y-PATTERN

The Y-pattern is a V-pattern subtype with divergence occurring in upgaze and little change in the horizontal deviation between primary position and downgaze. This pattern is highly suggestive of bilateral inferior oblique overaction, which is often associated with infantile esotropia and may also be seen with intermittent exotropia. Y-pattern can also be seen in patients with Brown’s syndrome, Duane’s syndrome with upshoot, and rarely congenital aberrant innervation of the lateral rectus muscle with the superior rectus nerve (see Example 2).

Example 2.

ARROW PATTERN

Another V-pattern subtype is convergence that largely occurs between primary position and downgaze. This author has termed this pattern “arrow” pattern. The presence of an arrow pattern and extorsion in downgaze is virtually diagnostic for bilateral superior oblique muscle palsy. The lack of abduction and intorsion in downgaze because of weak superior oblique muscles allows unopposed adduction and extorsion by the inferior recti muscles (see Example 3).

A-PATTERN SUBTYPE

LAMBDA PATTERN

The lambda pattern, an A-pattern subtype, is characterized by a divergence in downgaze without much change in the horizontal deviation from primary position to upgaze. A lambda pattern is most frequently associated with bilateral superior oblique overaction. Overrecessed or slipped inferior rectus muscles will also cause an A-pattern lambda subtype with apparent superior oblique muscle overaction. In contrast, inferior oblique muscle underaction causes an A-pattern with most of the horizontal change as convergence in upgaze (see Example 4).

Example 4.

X-PATTERN

An X-pattern occurs when there is divergence in upgaze and divergence in downgaze, which can occur without a specific cause. Patients with long-standing large-angle exotropia will frequently show an X-pattern, presumably caused by a tight contracted lateral rectus muscle. As the eye adducts against the tight lateral rectus muscle, it acts as a leash and produces lateral forces. If the eye then rotates up or down the tight lateral rectus slips above or below the eye and pulls the eye up and out, or down and out, respectively. This leash effect of the lateral rectus is also seen in Duane’s syndrome, usually type III, with both an upshoot and downshoot present on attempted adduction. Lateral rectus recessions reduce the X-pattern associated with exotropia, and an ipsilateral lateral rectus recession with a Y- split works well to reduce the vertical overshoot and X-pattern associated with Duane’s syndrome type III29 (see Example 5).

Treatment of A- and V-Patterns

A- and V-patterns with minimal or no oblique overaction can be managed by offsetting, or transposing, the horizontal rectus muscles superiorly or inferiorly. Transpose the medial recti insertions toward the apex of the pattern (up for an A-pattern and down for a V-pattern) and the lateral recti insertions to the wide part of the pattern (down for an A-pattern and up for a V- pattern) (Fig. 9-1). An A-pattern exotropia, for example, can be treated by recessing both lateral rectus muscles and transposing them inferiorly (Fig. 9-2). Vertical transposition of horizontal muscles in the treatment of A- or V-patterns changes vector forces and muscle tension as the eyes rotate up and down. For example, when the medial recti are infraplaced for a V-pattern, they gain increased function as the eyes rotate up, thus collapsing the V-pattern. Conversely, when the eyes rotate down, the infraplaced medial rectus muscles slacken, resulting in divergence of the apex of the V-pattern. One-half-tendon-width

FIGURE 9-1. Direction to transpose the rectus muscles to correct for A- and V-patterns. Left diagram: transposition for a V-pattern, with the lateral rectus muscles moved up and medial rectus muscles moved down. Right diagram: transposition for an A-pattern, with the medial rectus muscles moved up and the lateral rectus muscles moved down. The medial rectus is moved toward the apex of the A or V and the lateral rectus is moved away from the apex of the A or V. This transposition holds true whether the muscles are recessed or resected.

FIGURE 9-2. Drawing of a one-half-tendon-width inferior transposition of the lateral rectus muscle with recession for an A-pattern associated with an intermittent exotropia. A Insertion to limbus distance. B Recession measured from the insertion.

(5 mm) of vertical displacement results in approximately 15 PD of pattern correction. A full-tendon-width vertical displacement results in approximately 25 PD of correction and is reserved for extremely large A- or V-patterns. Vertical transposition of a horizontal rectus muscle by one full-tendon-width reduces the vector forces at the horizontal plane and, in this author’s opinion, often results in unpredictable horizontal alignment. For example, a full-tendon-width infra-placement of the lateral rectus muscles for an A-pattern would predispose to an overcorrection (esotropia) in primary position. This author rarely performs a horizontal rectus muscle transposition more than one-half tendon-width (5 mm) except in cases of a large A- or V- pattern associated with craniofacial disorders or absent muscles. Monocular supraplacement of one rectus muscle and infraplacement of the partner antagonist muscle can be used to correct an A- or V-pattern in a patient with amblyopia to avoid surgery on the only good eye. Monocular A- or V-pattern horizontal muscle offsets can cause significant torsional changes and should be done only on amblyopic eyes in patients with poor binocular fusion to avoid inducing torsional diplopia. Thus, monocular horizontal offsets can be used to correct torsional diplopia.

In cases with significant inferior or superior oblique overaction and an A- or V-pattern, the appropriate oblique muscles should be weakened rather than performing a horizontal rectus muscle transposition. An exception exists for patients with

superior oblique overaction and binocular fusion. These patients are at risk for developing cyclovertical diplopia after superior oblique tenotomy.23 Patients with binocular fusion and mild superior oblique overaction are best treated with transposition of the horizontal recti rather than a superior oblique tenotomy. Another surgical option for the fusing patient is a controlled tendon elongation procedure, such as the Wright superior oblique tendon expander or a split-tendon elongation. For large A- and V-patterns ( 25 PD) with 3 or more oblique overaction, consider combining oblique weakening with a half-tendon- width horizontal rectus muscle transposition.

OBLIQUE DYSFUNCTION

Clinical Evaluation of Oblique Dysfunction

When an oblique muscle overacts or underacts, all three functions of the muscle are involved: torsional, vertical, and horizontal. Clinical quantification of oblique dysfunction, however, is primarily based on the vertical hyperor hypofunction seen on version testing. To assess oblique function, move the eye under examination into adduction and make an observation. Then move the eye into the field of action of the muscle: adduction and elevation for the inferior oblique muscle, and adduction and depression for the superior oblique muscle. The amount of overaction or underaction can be graded on a scale of 1 to4 for overaction and 1 to 4 for underaction. A measurement of 1 overaction is recorded if there is no hypertropia with horizontal versions, but there is slight overaction when the eye is moved into the field of action of the oblique muscle vertically. With 2 overaction, there is a slight hypertropia in horizontal gaze, and with 3 overaction, there is obvious hypertropia on direct horizontal gaze. In 4 overaction, there is a large hypertropia in horizontal gaze with an abduction movement as the eye moves vertically into its field of action. Figure 5-3 in Chapter 5 shows degrees of inferior oblique overaction on version testing. The amount of A- or V-pattern and amount of fundus torsion are additional parameters to help quantitate the amount of oblique dysfunction.

When evaluating oblique dysfunction, the abducting eye should be fixing so the adducting eye is free to manifest oblique dysfunction. For example, when the right inferior oblique is

retinal orientation. A tilt right, for example, invokes intorsion of the right eye and extorsion of the left eye. The intortors are the superior oblique and the superior rectus muscles, and the extortors are the inferior oblique and the inferior rectus muscles. This arrangement keeps vertical forces balanced during the head tilt. If one of the torsional muscles is paretic, then there will be an imbalance of vertical forces and a vertical deviation will occur on head tilt testing. Figure 9-3 demonstrates this concept for a right superior oblique paresis. As the head tilts to the right, the right superior oblique and right superior rectus contract to intort the right eye. Because the superior oblique is paretic, the superior rectus has unopposed vertical force and elevates the eye, creating an increasing right hyperdeviation on head tilt to the right.

The head tilt test is used in patients with a vertical deviation to determine if either a vertical rectus or oblique muscle is paretic. When a patient presents with a vertical deviation, first perform the head tilt test to see if a paretic muscle is present. If the head tilt test is positive ( 5 PD difference in right tilt vs. left tilt), then it is likely there is a vertical rectus or oblique muscle paresis. To determine which muscle is paretic, measure the deviation in sidegaze and use the three-step test as described next.

FIGURE 9-3. Diagram of a right superior oblique paresis with a positive head tilt in tilt right. As the head tilts to the right, the left eye extorts and the right eye intorts. The extorters of the left eye are the inferior rectus and the inferior oblique. Their vertical functions cancel each other, so there is no vertical overshoot. The intortors of the right eye are the superior rectus (SR) and superior oblique (SO) muscles. Because the right superior oblique is paretic, the elevation effect of the superior rectus is unopposed, and a right hypertropia occurs on tilt to the right.