Vertical offsets of horizontal recti muscles in the management of A and V pattern strabismus

Vertical transposition of the horizontal rectus muscles is the preferred operation in cases of A and V pattern strabismus in which oblique muscle dysfunction is inadequate to merit oblique surgery. Fifty-nine patients undergoing standard horizontal surgery with half tendon width vertical offsets and eight patients undergoing two-thirds to full tendon width offsets were retrospectively studied. Technique for pattern measurement and surgery are discussed. Postoperative data were analysed on a short-term (less than six weeks) and long-term (greater than 12 months) basis. Standard horizontal surgery combined with half-tendon width vertical transposition is shown to be an effective operation for collapsing all subgroups of A and V pattern strabismus when indications are appropriate. The initial correction to within +/- 10 D of pattern was 96% over all with 78% remaining collapsed to within +/- 10 D over an average 36-month follow-up. Recess-resect, bimedial and bilateral rectus recession operations with offsets are all approximately equally effective in pattern collapse. A graded pattern collapse response was found with greater collapse being related to greater initial pattern. The risk of conversion, from a more desirable pattern (AET, VXT) to a less desirable pattern (AXT, VET) is low (7.3%). For patterns greater than 30 D, three quarters to full-tendon width offsets were effective in collapsing pattern. For A and V patterns with significant oblique muscle dysfunction, oblique surgery is advocated.