Fig. 4.

Mean lever arms of the medial (MR) and lateral rectus (LR) muscles of 38 orbits of 19 normal subjects monocularly fixating targets in 29° ab- and 34° adduction, and of 8 orbits of 7 subjects in 21° aligned convergence. Computations assume that the rotational center is constant for each direction of rotation, and that each muscle departs the globe at its scleral insertion. Note that the MR lever arm is much shorter than the LR lever arm in adduction, but increases by about 33% in convergence.