We simulated the three-dimensional contraction of the lateral rectus muscle using the finite element method. We proposed a hyperelastic, transversely isotropic constitutive model for extraocular muscle, which incorporates the force–length–activation relationship and the effect of changes in fraction of interweaving tendon. The model successfully reproduced the experimental force–length–activation relationship when applied to a unit cube for validation. We also propose a method to incorporate the effect of tendon weaving using the tendon fraction. The electrical potential method was applied to define the fiber direction and tendon fraction in muscle geometry derived from magnetic resonance imaging. Finally, the model was applied to a forced duction test of the lateral rectus muscle. Although our model requires further validation, the proposed constitutive model and definition of geometrical information are a step toward future medical application by facilitating three-dimensional modeling with improved accuracy.