Purpose: To show conditions where a vertical deviation, an A- or a V-pattern or cyclotropia can appear after surgery on the horizontal rectus muscles, with or without oblique muscle surgery. Our purpose is also to show conditions when a vertical deviation can be anticipated before horizontal rectus muscle surgery and realignment of the ocular deviation. Finally, our purpose is to stress on some surgical precautions one should take to avoid such complications.
Case reports: We report two cases who showed significant vertical deviations due to complications that followed surgical weakening procedures of the inferior oblique muscles.
Conclusion: 1. Vertical deviations, A and V patterns and cyclotropia can occur, can be anticipated or can be avoided in pure horizontal rectus muscle surgeries 2. Vertical deviations are common following complicated oblique muscles surgery if the surgeon blindly sweeps the muscle hook into the area. They can be avoided if the weakening technique allows direct visualization of the inferior oblique muscle.