Pseudopapilledema (Fig. 13.6) is due to a narrow scleral canal. Because of the constriction, the nerve fibers are tightly compressed. The optic disk is elevated and the full circle of the margin obscured. The optic cup is absent, and the retinal vessels appear tortuous. There are no abnormal morphologic changes such as bleeding, nerve fiber edema, and hyperemia; visual acuity and visual field are normal. Pseudopapilledema can occur with hyperopia,

Tilted disk.

Fig. 13.5 Oblique entry of the optic nerve superiorly with an inferior crescent and inferior segmental ectasia of the fundus.

13.3 DisordersthatObscuretheMarginoftheOpticDisk 365

Pseudopapilledema. -

Fig. 13.6 Circular blurring of the margin of the optic disk with absence of the optic cup.

although it is encountered equally frequently in emmetropic or slightly myopic eyes.

Differential diagnosis: optic disk edema, optic disk drusen (see Table 13.1). Myelinated Nerve Fibers

Normally retinal nerve fibers are not myelinated. However, myelinated areas occasionally occur in the retina (Fig. 13.7). They occur most frequently at the

— Myelinated nerve fibers. -

Fig. 13.7 Because they are myelinated, the nerve fibers appear whitish and striated and can simulate segmental blurring of the margin.

margin of the optic disk. Whitish and striated, they simulate segmental or circular blurring of the margin. Myelinated nerve fibers can also occur on the periphery of the retina. Because of their location in the innermost layer of the retina, they tend to obscure the retinal vessels. Myelinated nerve fibers normally cause no loss of function. Only extensive findings can lead to small sco-tomas.

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