Alfredo A. Sadun, Michelle Y. Wang, in Handbook of Clinical Neurology, 2011
Myelinated nerve fibers (optic disc medullation) result from an abnormal intraocular myelination of the peripapillary nerve fiber layer anterior to the lamina cribrosa. The abnormal presence of oligodendrocytes noted histopathologically in retinas with myelinated nerve fibers suggests their role in the pathogenesis. It is speculated that a structural or biochemical defect in the lamina cribrosa may allow oligodendrocytes to migrate intraocularly and continue myelination past the lamina cribrosa (Williams, 1986). The myelinated nerve fibers may be inherited in an autosomal-dominant pattern or acquired from early-age trauma to the eye causing damage to the lamina cribrosa (François, 1961; Baarsma, 1980).
Myelinated nerve fibers are usually unilateral, isolated, and sporadic. Visual acuity usually is normal and visual field defects, though present, are mild arcuate scotomas, depending on the extent and location of the lesion. Most patients have an enlarged blind spot as myelinated fibers are usually adjacent to the optic disc.
Ophthalmoscopically, myelinated nerve fibers appear white and opaque with feathery edges and run in arcuate bundles. The lesions are often continuous with the optic disc and may be associated with retinal vascular abnormalities.
Myelinated nerve fibers are common in Down syndrome and Gorlin–Goltz syndrome (multiple basal cell nevi). A unilateral condition may be associated with severe amblyopia and high myopia that is often refractory to standard occlusion therapy (Ellis et al., 1987).
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