Hypocycloidal tomograms were obtained at every millimeter of a cadaver head positioned so that the axis of the optic canal was perpendicular to the radiographic film. Without change of position, the head was frozen and sliced. Four 1-mm thick sections of the optic canal and orbital apex were obtained. A direct comparison between the contact radiograph of each anatomic section was made and its corresponding tomogram taken when the head was intact, pointing out the anatomic structures. On the tomogram at the orbital end of the optic canal, an artifactual shadow cast by the thick heavy optic strut was noted. An artifactual shadow at the orbital apex appearing to close the superior orbital fissure was noted also; this artifactual shadow is cast by the lateral wall of the orbit.
Potter GD, Trokel SL. Anatomic and Radiographic Analysis of the Optic Canal and Orbital Apex. Arch Ophthalmol. 1970;83(5):584-587. doi:10.1001/archopht.1970.00990030584010