Normal orbital anatomy plays a foundational role in stabilizing binocular eye movements. Abnormal orbital anatomy, contrariwise, destabilizes binocular eye alignment by introducing eccentric and unbalanced EOM forces. These abnormalities can be categorized into five broad etiologies: (1) orbital structural disorders; (2) globe size disorders; (3) degenerative disorders; (4) innervational disorders; and (5) trauma. Orbital imaging provides important diagnostic information on EOM path and innervational status, but only if performed properly. The three critical elements are (1) maximize the field of view by focusing on the orbit of interest; (2) control gaze, ideally imaging in primary position; and (3) image perpendicular (direct coronals) and parallel (axial for horizontal, sagittal for vertical) to the EOM(s) of interest. Images should be analyzed systematically by comparing EOM size and location between orbits and with established normative values. The single most critical image is the most anterior direct coronal plane that contains both globe and clearly defined EOM cross sections. EOM positional abnormalities in this plane establish the diagnosis for the first three categories of orbital abnormalities. Innervational abnormalities are best evaluated in the mid-orbit; asymmetry in mid-orbital EOM size and shape defines or confirms innervational disorders like complete or partial cranial nerve palsies.
Keywords: EOM; MRI; orbit; pulley; strabismus.