Images of the optic nerve: anatomic-CT correlation.

The course of the intraorbital part of the optic nerve, as demonstrated on anatomic sections in various planes, is correlated with the appearance of the nerve in computed tomographic (CT) images. Discrepancies between the anatomic and CT appearance are analyzed and discussed. Since the optic nerve has a sinuous course in both the horizontal and vertical planes, no thin axial or sagittal section can be entirely parallel to the nerve. Any section will transsect the optic nerve obliquely, leading to an apparent hypodensity or "thinning" of certain segments as shown on CT. The appearance of the course of the nerve on reformatted CT images depends on the plane of the original CT section. Computed tomograms that are obtained with the eye in primary position do not allow reliable judgments regarding the course and size of the optic nerve.