Fig. 50. Curves show what happens when medial rectus muscle insertion is 1, 2, to 10 mm posterior to usual insertion. For example, a 7-mm recession puts muscle at tangency point; reduction of torque then occurs with adduction due to loss of lever arm. Even so, the eye can rotate 30 degree before torque is reduced to 80% of normal. (Adapted from Beisner DH: Arch Ophthalmol 85:13, 1971.)