V-Pattern Esotropia and Exotropia Treatment & Management

In mild cases, no treatment may be required.

In intermittent deviations, which are exotropic in nature, overcorrection with minus lenses (-2 to –4 D) can be tried. The rationale is that the minus lenses stimulate accommodative convergence and reduce the exodeviation angle; however, this does not address the vertical incomitance.

For small comitant deviations, prisms can be tried to control the deviation and to relieve asthenopic symptoms. Base-in prisms are used for exotropia; base-out prisms are used for esotropia.

Indications for surgery include the following: to correct the underlying deviation and to enable fusion, to achieve and regain comfortable binocular single vision, and to correct abnormal head posture when present.

In both esotropia and exotropia, the V-pattern incomitance is considered surgically significant when the difference between horizontal deviations in upgaze and downgaze is equal to or greater than 15 PD. Prior to surgery, determine if the V-pattern is associated with oblique muscle dysfunction. The most common pattern encountered is inferior oblique muscle overaction and relative superior oblique muscle underaction or overelevation and underdepression in adduction.

Surgical treatment of V-pattern strabismus with oblique muscle dysfunction

These patients usually require appropriate horizontal rectus muscle surgery that is combined with inferior oblique muscle weakening procedures. For V-pattern esotropia, medial rectus muscle recessions (and/or lateral rectus muscle resections) along with inferior oblique muscle weakening (or superior oblique muscle tucks) are performed. For V-pattern exotropia, lateral rectus muscle recessions (and/or medial rectus muscle resections) and inferior oblique muscle weakening are performed. Inferior oblique muscle weakening procedures should be performed equally on both eyes.

Several studies have confirmed the role of and reported surgical success with, inferior oblique muscle weakening (recessions) in both V-pattern esotropia and V-pattern exotropia. In one study, the stereoscopic function improved in 33.3% of patients, and, in another study, a significant improvement in fusional status was noted postoperatively after a combination of horizontal rectus muscle surgery and inferior oblique muscle weakening. ^{[3, 4]}

Inferior oblique muscle weakening procedures include inferior oblique muscle recession, anteriorization, myotomy, and myectomy. The degree of inferior oblique muscle overaction determines the procedure of choice. For mild-to-moderate inferior oblique muscle overactions, recessions are preferred. Depending on the severity of the inferior oblique muscle overaction, graded recessions can be performed.

Quantification (grading) of the inferior oblique muscle recession for V-pattern strabismus was studied by a group of investigators. ^[5] These investigators recessed the inferior oblique muscle from 8 mm for a V-pattern of 12 PD with +1 inferior oblique muscle overaction to 12 mm for a V-pattern of 30 PD with +3 inferior oblique muscle overaction. A satisfactory outcome was observed in 75% of patients with a preoperative V-pattern of less than 20 PD. A success rate of 57% was noted in patients with a preoperative V-pattern of more than 29 PD. Undercorrections were common, hence their recommendation that increased amounts of surgery be done.

For severe inferior oblique muscle overaction, the anteriorization procedure is sometimes preferred. A study compared graded recession to anterior transposition of the inferior oblique muscle for V-pattern strabismus and concluded that anterior transposition is as effective as graded recession. ^[6]

Inferior oblique muscle myotomy or myectomy also can be performed. A study by Lee et al showed inferior oblique Z-myotomy was effective in correcting a V-pattern strabismus in patients with inferior oblique overaction under the degree of + 2. ^[7]

If a reoperation is required after inferior oblique muscle myectomy, localizing the muscle may be difficult.

Inferior oblique muscle weakening procedures have very little, if any, effect on the horizontal deviation in the primary gaze.

Surgical treatment of V-pattern strabismus without oblique muscle dysfunction

Vertical displacement of horizontal rectus muscle insertions: Introduced by Knapp, ^[8] this technique shows favorable results in patients with mild-to-moderate V patterns with no apparent oblique muscle dysfunction.

In determining the direction of displacement, the authors follow a general rule wherein the medial rectus muscle insertion is always moved toward the closed end of the V (downward) and the lateral rectus muscle insertion is always moved toward the open end of the V (upward), as outlined in the image below.

Note the following:

• V-pattern esotropia - Bilateral medial rectus muscle recessions with downshift

• V-pattern esotropia - Bilateral lateral rectus muscle resections with upshift

• V-pattern exotropia - Bilateral lateral rectus muscle recessions with upshift

• V-pattern exotropia - Bilateral medial rectus muscle resections with downshift

The amount of displacement depends on the difference in the amount of deviation in upgaze and downgaze. A half tendon width displacement corresponds to a 5-mm vertical shift of the insertion, and a full tendon width displacement corresponds to a 10-mm vertical shift of the insertion. While performing the vertical displacement, maintaining the relationship between the original insertion of the muscles and the sclerocorneal limbus is important. The image below illustrates half tendon width vertical shift of muscle insertion as well as full tendon width vertical shift of muscle insertion.

One study showed that vertical displacement of horizontal muscle in V-pattern exotropia without oblique muscle dysfunction corrected an average V of 20 pd. ^[9]

Oya et al studied the effects of vertical offsets of horizontal rectus muscles in V-pattern exotropia without oblique muscle dysfunction. They conclude that this technique effectively corrects the pattern deviation and that postoperatively no patient had an A pattern or any torsional disturbance. ^[9]

Slanting the horizontal rectus muscle insertions with or without recessions: For a V pattern, selective recession of the superior fibers of the medial rectus muscle or the inferior fibers of the lateral rectus muscle can be performed. The amount of correction from this type of surgery is minimal. An observational case study evaluated the therapeutic effects of surgically slanting the muscle insertions on the effect of the V-pattern in patients with exotropia. ^[10] A slanting surgical reinsertion line with a 3- to 4-mm difference between the upper and lower corners of the muscles was created. The study showed that the mean amount of reduction in the V-pattern was 10.3 PD in the primary position and 29.8 PD in upgaze. This procedure can be combined with recessions and/or vertical rectus muscle displacement of the horizontal rectus muscle insertions. The image below depicts slanting of the rectus muscle insertion with and without recession.

One study showed that both medial rectus slanting recession and medial rectus recession with downward transposition corrected V-pattern esotropia, with no clinically or statistically significant differences in success rate. ^[11]

Horizontal transpositions of the vertical recti muscles: The vertical recti muscles are secondary adductors. By altering their site of insertion, the adducting forces can be modified. In V-pattern esotropia, the inferior recti muscles can be moved temporally. In V-pattern exotropia, the superior recti muscles can be moved nasally.

This procedure is not commonly preferred because of the following:

• The results are difficult to predict.

• If fusion is present, the horizontal, vertical, and torsional component change that results from the transposition may change the sensory status.

• Usually, a horizontal deviation occurs that requires surgery. In this case, additional surgery on the vertical recti muscles may increase the risk for anterior segment ischemia.

This procedure may be considered as an option in patients in whom the inferior oblique muscles have been maximally weakened and are not overacting, and a residual V pattern persists.

When considering monocular surgery with an associated V pattern and planning a recess-resect procedure, the medial rectus muscle is displaced downward and the lateral rectus muscle is displaced upward in the same eye. Goldstein reported that an 8-mm displacement of the horizontal recti muscles monocularly corrects V-patterns as large as 30 PD. ^[12] The image below illustrates a recess-resect procedure in the same eye.