Of the various abnormalities of the optic disc, papilledema has the greatest neurologic implication, for it signifies the presence of increased intracranial pressure. The term papilledema has come to mean disc swelling due to raised intracranial pressure although there are other causes of a similar funduscopic appearance. An ophthalmoscopic appearance identical to that of papilledema can be produced, for example, by infarction of the optic nerve head (as with anterior ischemic optic neuropathy) and other conditions affecting the intraorbital portion of the optic nerve (especially inflammatory or infiltrative conditions). Certain clinical and funduscopic findings, listed in Table 12-2 and described in the following text, assist in distinguishing between these processes, although all share the basic feature of conspicuous optic disc swelling.
In its mildest form, papilledema appears as slight elevation of the disc and blurring of the disc margins, especially of the superior and inferior aspects, and a mild fullness of the veins in the disc. Subtle disc elevation is also indicated by a loss of definition of the vessels overlying the disc as they approach the disc margin from the periphery; this appearance is produced by edema in the adjacent retina. Because many normal individuals, especially those with hypermetropia, have ill-defined disc margins, the early stage of papilledema may be difficult to detect (Fig. 12-11). Pulsations of the retinal veins, best seen where the veins turn to enter the disc, will have disappeared by the time intracranial pressure is raised, but this finding is not specific, as venous pulsations are not present in a proportion of normal individuals in the seated position. On the other hand, the presence of spontaneous venous pulsations is usually a reliable indicator of an intracranial pressure below 200 mm H2O, and thus argue against true papilledema from elevated intracranial pressure (Levin). Fluorescein angiography, red-free fundus photos (which highlight the retinal nerve fibers), and ocular coherence tomography are helpful in detecting early edema of the optic discs.
More severe degrees of papilledema appear as further elevation, or “mushrooming” of the entire disc and surrounding retina. There is obscuration of vessels at the disc margins and, in some instances, peripapillary hemorrhages (Fig. 12-12). Advanced papilledema is almost always bilateral although it may asymmetric. In contrast, purely unilateral edema of the optic disc suggests an optic nerve sheath meningioma or other tumor involving the optic nerve, although it will sometimes be observed an early stage of increased intracranial pressure. As papilledema becomes chronic, elevation of the disc margin becomes less prominent and the optic nerve head develops pallor, representing a dropout of nerve fibers (atrophy) (Fig. 12-13). Varying degrees of secondary optic atrophy occur in the wake of papilledema that has persisted for more than several days or weeks, ultimately leaving the disc pale and gliotic.
Acute papilledema, while it may enlarge the blind spot slightly, usually does not have a great affect upon visual acuity (except transiently during spontaneous waves of increased intracranial pressure). Therefore, acute optic disc swelling in a patient with severely reduced vision should not be attributed to papilledema; instead, intraorbital optic neuritis (papillitis) or infarction of the nerve head (ischemic optic neuropathy) is more likely explanations. In rare cases of pseudotumor cerebri, visual loss may be unexpectedly abrupt, appearing in a day or less. This seems to happen most often in patients with constitutionally small optic nerves, no optic cup of the nerve head and, presumably, a small aperture of the lamina cribrosa. Such explosive visual loss in pseudotumor cerebri may respond to urgent optic nerve fenestration, but this approach is controversial, as discussed in “Pseudotumor Cerebri” in Chap. 30.