Y Pattern
Patients with Y patterns (pseudo-overaction of the inferior oblique) have normal ocular alignment in primary position and downgaze but diverge in upgaze. They appear to have overacting inferior oblique muscles, but the deviation actually results from aberrant innervation of the lateral rectus muscles in upgaze. Clinical characteristics that help identify this form of strabismus include the following: (1) the overelevation is not seen when the eyes are moved directly horizontally, but it becomes manifest when the eyes are moved medially and slightly elevated; (2) there is no fundus torsion; (3) there is no difference in vertical deviation with head tilts; and (4) there is no superior oblique muscle underaction.
Kushner BJ. Pseudo inferior oblique overaction associated with Y and V patterns. Ophthalmology. 1991;98(10):1500–1505.
X Pattern
An X pattern is present when the deviation in primary position increases in both upgaze and downgaze. This pattern is usually associated with overelevation and overdepression in adduction when the eye moves slightly above or below direct side gaze. X patterns are most commonly seen in patients with large-angle exotropia, and the apparent overaction results from contracture of the lateral rectus muscle, with slippage of the globe as the eye adducts.
λ Pattern
This rare pattern is a variant of A-pattern exotropia. It is present when the deviation is the same in primary position and upgaze and increases in downgaze. The λ pattern is usually associated with ODAd.
Management
Clinically significant patterns typically are treated surgically, in combination with correction of the underlying horizontal deviation.
General Principles
The following are guidelines for planning surgical correction of pattern deviations. See Chapter 14 for further discussion of some of the procedures and concepts mentioned here.
1.For patients with patterns associated with apparent overaction of the oblique muscles (OEAd, ODAd), weakening of the oblique muscles is performed.
2.For patients with no apparent overaction of the oblique muscles or a pattern inconsistent with oblique dysfunction, vertical transposition of the horizontal muscles is performed. The muscles are transposed from one-half of the width to the full width of the insertion. The medial rectus muscles are always moved toward the “apex” of the pattern (ie, upward in A patterns and downward in V patterns). The lateral rectus muscles are moved toward the open end or “empty space” (ie, upward in V patterns and downward in A patterns). A useful mnemonic is MALE: Medial rectus muscle to the apex, lateral rectus muscle to the empty space. These rules apply whether the horizontal rectus muscles are weakened or tightened (Fig 10-6).
3.When horizontal rectus muscle recession-resection surgery is the preferred choice because of other pertinent factors (eg, prior surgery, unimprovable vision in 1 eye), displacement of the rectus muscle insertions should be in mutually opposite directions, according to the rules stated
previously. Unlike what occurs when both horizontal rectus muscles of an eye are moved in the same direction, this displacement has little, if any, vertical effect in the primary position.
4.Some surgeons adjust the amount of horizontal surgery because of the potential effect of oblique muscle weakening on the horizontal deviation, particularly for superior oblique muscle surgery, but this is controversial. Some believe that bilateral superior oblique weakening causes a change of 10Δ–15Δ toward convergence in primary position and suggest modifying the amount of horizontal surgery to compensate for this expected change. For inferior oblique muscle weakening procedures, the amount of horizontal rectus muscle surgery does not need to be altered, because the inferior oblique muscle weakening does not substantially change primary position alignment.
5.Surgery on the vertical rectus muscles (eg, temporal displacement of the superior rectus muscles for A-pattern esotropia or temporal displacement of the inferior rectus muscles for V- pattern esotropia) is rarely employed, because the horizontal rectus muscle operations required for the underlying esotropia or exotropia can correct the pattern with appropriate displacement of the muscles.
Figure 10-6 Direction of displacement of medial rectus (MR) and lateral rectus (LR) muscles in operations to treat A-pattern (left) and V-pattern (right) deviations. A useful mnemonic is MALE: medial rectus muscle to the apex, lateral rectus muscle to
the empty space. (Reprinted with permission from von Noorden GK, Campos EC. Binocular Vision and Ocular Motility: Theory and Management of Strabismus. 6th ed. St Louis: Mosby; 2002:388.)
Treatment of Specific Patterns
Table 10-1 summarizes the surgical treatment of pattern strabismus (see also Chapter 14).
Table 10-1
V pattern
For V-pattern exotropia or esotropia associated with OEAd, weakening of the inferior oblique muscles is performed, usually either a myectomy or recession. This corrects up to 15Δ–20Δ of V pattern. For patients who also have dissociated vertical deviation (DVD), anterior transposition of the inferior oblique muscle may improve both the V pattern and the DVD. Because patients with V-pattern infantile esotropia who are younger than 2 years are at risk of developing DVD, anterior transposition of the inferior oblique may be considered in this group to preemptively address the DVD.
For patients without OEAd, appropriate vertical transposition of the horizontal rectus muscles is performed (see Fig 10-6).
A pattern
For A-pattern exotropia or esotropia associated with ODAd, weakening of the superior oblique muscles is performed. Tenectomy of the posterior 7/8 of the insertions is an effective method for treating approximately 20Δ of A pattern, with no significant effect on torsion. Lengthening of the tendon by recession, insertion of a spacer, or a Z-lengthening procedure may also be used. Bilateral superior oblique tenotomy is a very powerful procedure that may correct up to 40Δ–50Δ of A pattern. There is a risk of induced torsional imbalance with this procedure, which may cause problems for patients with fusional ability.
For patients without OEAd, appropriate vertical transposition of the horizontal rectus muscles is performed (see Fig 10-6).
Patients with trisomy 21 associated with early-onset esotropia may develop A-pattern strabismus with ODAd. The pattern in these patients is usually due to orbital abnormalities associated with trisomy 21. Vertical transposition of the horizontal rectus muscles is employed for such patients.
Y pattern
Because Y patterns are not due to overaction of the inferior oblique muscles, weakening these muscles is not an effective treatment. Superior transposition of the lateral rectus muscles is generally used for patients with this pattern.
Xpattern
Xpatterns are usually due to pseudo-overaction of the oblique muscles caused by contracture of the
lateral rectus muscles in patients with large-angle exotropia. Recession of the lateral rectus muscles alone usually improves the pattern.
λ pattern
These patterns are typically associated with ODAd. Appropriate superior oblique weakening procedures may be used in patients with this pattern.