Multipositional high-resolution magnetic resonance imaging of the human orbit's functional anatomy

purpose Normal eyelid and orbital structures were studied without any disturbance in three positions of gaze and during Bell's phenomenon (eyes closed). methods Seven orbits were imaged using a high-resolution magnetic resonance imaging program and a surface coil. They were analyzed with sub-millimetric resolution in a series of contiguous vertical planes parallel to the orbital axis. The three positions of gaze (downgaze, straight ahead and up-gaze) were reproduced using the same fixation device. results Between upgaze and downgaze, a volume of intraconal fat is cleared away from the path of the optic nerve and can be measured semi-quantitatively. Concurrently, significant volumetric changes occur in the fat compartment comprised between a rectus muscle and its arc of contact with the sclera. The superior and inferior extraconal fat pads follow the movements of the corresponding eyelid retractor complex. Along with the relative movements of the intraconal and extraconal fat pads, the bulging of the contracting extraocular muscles and thinning of the relaxing ones, a translatory movement of the globe opposite to the direction of gaze is seen. The courses of Whitnall's and Lockwood's ligaments are demonstrated in relation to their retractor muscle complex and extraconal fat pads, allowing refined observation of the elastic and inelastic components of their attachments. In Bell's phenomenon, the levator and superior rectus muscles are seen sliding in opposite directions as the levator relaxes and the superior rectus contracts. How other structures are affected by this complex movement is illustrated. conclusions Multipositional high-resolution magnetic resonance imaging is useful in furthering the understanding of the functional anatomy of the human orbit.