Rectus muscle transposition surgery.

Thirty patients had vertical offsets of their horizontal rectus insertions to correct a coexisting vertical deviation while 14 patients had horizontal offsets of their vertical recti to correct a horizontal deviation (total of 44 patients). The average effect of surgery was about 0.5 prism diopters per mm of surgery, both for a vertical or a horizontal effect. This is about half as much as generally reported in the literature, where one prism diopter of effect usually follows each mm of transposition. In our study, a greater effect per mm of surgery was noted with larger associated vertical deviations and larger amounts of vertical transposition of the horizontal rectus muscles.