Purpose: To study the effect of vertically transposing both horizontal eye muscles of one eye in the same direction on vertical strabismus.
Methods: Retrospective analysis of 33 patients in whom vertical transposition of the medial and lateral rectus muscles was combined with a recession/resection or recession/plication procedure. Preoperative ocular alignment was compared with that 1 day and 3 months postoperatively.
Results: Mean preoperative vertical deviation was 7.8 ± 4.3 (median 7.5, range 3-25) prism diopters (PD) at distance and 7.8 ± 4.1 (7, 0-18) PD at near. Vertical transposition of the horizontal rectus muscles averaged 5.6 ± 1.6 mm and reduced the vertical deviation to 3.4 ± 4.2 PD (2, 0-16) at distance and 2.9 ± 3.7 PD (2, 0-14) at near. Mean effect on the vertical deviation was 0.9 ± 0.7 (0.8, -0.8 to 2.13) PD/mm at distance and 0.9 ± 0.9 (0.83, -1 to 3) PD/mm at near, it was similar in patients operated on for esotropia and for exotropia. The surgical effect on the horizontal deviation was 2.1 ± 1.1 PD/mm (distance) and 2.6 ± 1 PD/mm (near). Both the vertical and horizontal surgical dose correlated with the effect in a linear way, but the variability was greater for the vertical transposition.
Conclusions: Vertical transposition of the horizontal rectus muscles in the same direction allows for correction of vertical strabismus. This procedure may be performed during primarily horizontal strabismus surgery, without operating on an additional extraocular muscle. The transposition distance correlates with the surgical effect but predictability of the effect is limited.
Keywords: Vertical strabismus; hypertropia; hypotropia; vertical transposition of the horizontal extraocular muscles.