A and V Patterns

A and V Patterns

Marshall M. Parks

Paul R. Mitchell

A and V patterns are manifested by a horizontal change of alignment of the eyes that occurs on midline upgaze and downgaze as the eyes are moved from the primary position. Although vertical incomitance was described by Duane in 1897,1 the importance of recognizing vertically incomitant horizontal deviations was not emphasized until studies by Urrets-Zavalia in 19482,3 and by Urist in 1951.4,5,6 Jampolsky7 suggested the term tent or tepee (

) syndrome, and Albert8 suggested the terms A pattern and V pattern, which have gained universal acceptance. As the eyes move from upgaze into downgaze in the A pattern, the exotropia (XT) increases or the esotropia (ET) decreases. In the V pattern, the XT decreases or the ET increases in moving from upgaze into downgaze. The A and V patterns may be associated with orthophoria, esodeviation, or exodeviation in the primary position. Compensatory head postures that provide sufficiently improved alignment to permit normal retinal correspondence (NRC) single binocular vision are frequently found in patients having A and V patterns.


Several principles have been advanced to explain the cause of the A and V patterns. According to one principle, contraction and relaxation of the horizontal rectus muscles occur as midline upgaze and downgaze are executed. There is some electromyographic evidence to support this claim.9,10 Scott11 was the first to document abnormal innervation to the lateral rectus muscles as the cause of divergence in upgaze in a patient with V-pattern exotropia. Another thesis attributes the A and V patterns to abnormalities in the cyclovertical muscles. Clinical evidence supports this explanation because overactions of the inferior oblique muscles are frequently associated with the V pattern, and overactions of the superior oblique muscles are frequently associated with the A pattern. Furthermore, weakening the overacting oblique muscles more effectively improves the disorder than weakening the horizontal rectus muscles.

Kushner12 suggested that A and V patterns were the result of complex interplay between all of the extraocular muscles. Ocular torsion by means of fundus photography13,14 was used to analyze 50 patients with A or V patterns. Primary oblique overaction produces torsion of the globe, resulting in vertical displacement of the horizontal rectus muscle insertions and a horizontal displacement of the vertical rectus muscle insertions. In theory, this should alter the vectors of the forces exerted on the globe by the rectus muscles so that the horizontal rectus muscles become partial elevators or depressors and the vertical rectus muscles become increasing abductors or adductors. This change in force vectors would tend to enhance the A or V pattern that results from oblique muscle dysfunction.

Saunders and Holgate15 studied ten unoperated children with V-pattern strabismus and ten control patients by coronal computed tomography scanning. Their data suggested that apparent rectus muscle malposition was a function of age and could not be implicated as an important cause of V-pattern strabismus.

Guyton and Weingarten16 hypothesized that sensory torsion in the absence or loss of fusion, where normal sensorimotor control mechanisms become aberrant, with rotation of the horizontal and vertical rectus muscles about the visual axes, creates the clinical appearance of oblique muscle over- or underaction and A and V patterns. Miller and Guyton17 tested this hypothesis by reviewing 332 patients who were overcorrected after surgery for intermittent exotropia. The control group was age matched and maintained fusion after exotropia surgery. The mean follow-up of 27 months in the consecutive esotropia group of 21 patients revealed 43% (nine of 21) had an A or V pattern; whereas in the mean follow-up in the control group, only 5% (one of 21) had an A or V pattern. These findings strongly suggest that loss of fusion is instrumental in the subsequent development of A or V patterns and are consistent with the sensory torsion theory of A- and V-pattern development.17


The only treatment for A or V pattern is surgery. Six surgical principles have been developed to explain how improvement is rendered.


Urist5,6 suggests weakening or strengthening the horizontal rectus muscles, claiming that the medial rectus muscles are most effective in midline downgaze because this is the usual position for convergence. He further claims that the lateral rectus muscles are most effective in midline upgaze because divergence is usually accomplished by looking upward from the downturned near-seeing position to see something at distance. By appropriately recessing or resecting these muscles to alter their power, not only is the horizontal measurement in the primary position improved, but also, theoretically, the A and V patterns are improved. For example, an ET-V pattern is improved with recessions of the medial rectus muscles, an ET-A pattern with resections of the lateral rectus muscles, an XT-V pattern with recession of the lateral rectus muscles, and an XT-A pattern with resections of the medial rectus muscles.


Knapp23 conceived the idea of vertical transposition of the insertions of the horizontal rectus muscles, proved its effectiveness, and popularized its usefulness in treating A and V patterns. He reasoned that vertical transposition of the insertions of the horizontal rectus muscles alters their scleral attachment relative to the rotation center of the globe, thus increasing the arc of contact of the transpositioned muscle in one vertical gaze position and decreasing it in the opposite vertical gaze position. Because the pull power of the muscle is related to the stretch put on it by the arc of contact, the horizontal pull power is enhanced and diminished in opposite vertical gaze positions, as compared with the unoperated horizontal rectus muscle. Hence, the horizontal rectus muscles become more effective abductors or adductors in the vertical gaze position opposite the direction in which their insertions are moved. Stated differently, the transpositioned horizontal rectus muscles become less effective horizontal rotators in the same vertical gaze position as the direction in which they are moved. For example, the infraplaced medial rectus muscles are more effective adductors in upgaze than in downgaze, or the supraplaced lateral rectus muscles are less effective abductors in upgaze than in downgaze. Therefore, an ET-V pattern is improved with either recessions and infraplacement of the medial rectus muscles or recession-resection on one eye, which also infraplaces the medial rectus muscle and supraplaces the lateral rectus muscle.

The directions in which the horizontal rectus muscle are transpositioned for A or V patterns associated with horizontal tropia are summarized in Table 1. The consensus seems to be that the usual quantity of transposition is half the width of the tendon. Although some surgeons perform total-width transplants, they experience greater unpredictable results in horizontal alignment in the primary position. Half-width tendon transpositions yield 15Δ to 20Δ change in the A or V pattern between upgaze and downgaze. Full-width transpositions produce more improvement, but the unpredictability of the horizontal correction in the primary position plus frequent limitation of duction in the field of action of the transpositioned muscle limits the usefulness of this quantity of surgery. Sharma and colleagues24 concluded that a 5-mm shift was as effective as an 8-mm shift in monocular vertical displacement of horizontal rectus muscles in A and V patterns, even when mild or moderate cyclovertical muscle imbalance was present. However, in all cases with oblique muscle dysfunction, residual vertical incomitance was observed, and therefore, the authors recommended vertical shifting only when there was no associated cyclovertical muscle imbalance.

Table 1. Directions in Which the Horizontal Rectus Muscles Are Transpositioned for Esotropic and Exotropic A and V Patterns

  Medial Rectus Lateral Rectus
ET, esotropia: XT, exotropia.

Vertical transposition of the horizontal rectus muscles may be performed symmetrically and bilaterally, or surgery may be confined to one eye, with appropriate vertical displacement of the medial and lateral rectus muscles.1,25,26 The determination of the amount of horizontal surgery is the same whether or not monocular vertical displacement is performed,27 even though Knapp23 has suggested increasing the usual amount of horizontal surgery when vertically displacing the horizontal muscles. Postoperative torsional symptoms or significant torsional measurements have not been produced. Oblique muscle dysfunction associated with the A or V pattern is not changed by vertically offsetting the horizontal rectus muscles.

In a retrospective study of 67 patients, Scott and colleagues28 reported an initial correction of 96%, within ± 10Δ of pattern. The standard horizontal rectus muscle surgery combined with half-width tendon offsetting surgery of the horizontal rectus muscles was shown to be an effective operation for collapsing all subgroups of the A- and V-pattern strabismus with appropriate indications. With A and V patterns without significant oblique dysfunction requiring surgery, the authors advocated standard horizontal surgery with half-width tendon offsets in A and V patterns from 10Δ to 30Δ. If the pattern exceeded 30Δ, they recommended three-fourths to full-tendon–width offsets combined with the standard horizontal rectus muscle surgery. When oblique muscle dysfunction was present, they recommended appropriate oblique muscle strengthening or weakening procedures along with appropriate horizontal or vertical rectus muscle surgery.

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Jul 10, 2016 | Posted by in OPHTHALMOLOGY | Comments Off on A and V Patterns

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