Some areas of AAO.org are temporarily unavailable. We apologize for the inconvenience and are working to restore access.

  • File Size: 99 KB
    Neuro-Ophthalmology/Orbit

    Midglobe Through Optic Foramen. This 3-mm section was obtained with optimal negative angulation to show both the midglobe and OF. The presence of the suprasellar structures and the absence of the nasopharynx also serve to identify the negative angulation. On thicker sections, the partial volumes of the voxels containing ON and the superior rectus and levator palpebrae superiorus muscles may combine to create the false impression that ON is enlarged by tumor. Identification of relevant structures will overcome this problem. ON may appear thickened by tumors, increased intracranial pressure causing enlargement of its sheaths, or inflammation. Atrophy or hypoplasia may cause the nerve to appear small, but caution should be exercised in making this interpretation from axial sections alone, without the benefit of coronal sections. Axial sections may contain only a partial volume of ON in the plane of section. The normal anteroposterior measurement of G is 50% to 55% ofanteroposterior orbit measurement (cornea to anterior margin of OF). The diameters of G cannot be compared; nor can exophthalmos be measured on the axial view if the globes are scanned at different levels due to vertical displacement or tilt of the head. SS is shown surrounded by the body of the sphenoid bone. OF is only about 3 mm in diameter in comparison with SOF, which is about 3 cm in height. Superiorly, SOF flanks OF on the lateral side, from which it is separated by AC. Inferiorly, SOF lies directly below OF, allowing the larger structure to be confused for the smaller one in positively angled scans. AC = Anterior Clinoid, G = Globe, L = Lens, OA = Ophthalmic Artery, OF = Optic Foramen, ON = Optic Nerve, SOF = Superior Orbital Fissure, SS = Sphenoid Sinus.