After the IO is chronically shortened in this manner, its elastic force is increased (and hence total force is also increased), resulting in the elevation in adduction and a V pattern that is typically associated with IO-OA. If the IO is indeed less elastic, it will resist stretching out the normal amount as the eye moves into adduction, which would force the eye to elevate. This is perhaps accentuated by the antagonist SO having a weaker than normal resistance to stretch due to sarcomere remodeling. Theoretically, the extorsion alone might explain the elevation in adduction and a V pattern seen with IO-OA.49,51 With an excyclotropia, all the rectus muscle insertions should be rotated (counterclockwise in the right eye and clockwise in the left eye). The elevation of the medial rectus insertion and lowering of the lateral rectus insertion would create a vertical vector that should result in elevation in adduction. The nasal displacement of the IR insertion and temporal displacement of the SR insertion would create horizontal vectors that should result in a V pattern. There are 5 compelling reasons, however, that suggest that these force vector changes are not the primary explanation for the elevation in adduction or the V pattern. First, the aforementioned observation that fundus extorsion typically precedes the elevation in adduction, often by many months to several years, should not be found if the pattern and version abnormality was primarily caused by the torsion. Second, if the change in force vector of the rectus muscles caused the torsion, the rise of the eye should be linear as the eye moves from primary into adduction. If fact, the eye typically seems to rise exponentially. Third, transposition procedures that are successful in treating A or V patterns should actually worsen the accompanying torsion. For example, a V-pattern esotropia can be successfully treated with recession and infraplacement of the medial rectus muscles.5,51 However, that surgical procedure should increase extorsion.52,53 If the elevation in adduction and V pattern were directly caused by the extorsion, that surgical procedure should be ineffective. Fourth, I have observed that sometimes fundus extorsion may persist to a substantial degree after surgical weakening of the IOs, yet the elevation in adduction and V pattern may be completely eliminated.54 Finally, I have observed that patients with bilateral fourth nerve palsy often have larger amounts of extorsion in each eye than one typically sees in patients with unilateral fourth nerve palsy. In spite of this, they usually have relatively small degrees of elevation in adduction.24,55,56 If extorsion was primarily responsible for elevation in adduction, they would be expected to manifest large upshoots on adduction.