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The optic nerve fibres in the retina are normally non-myelinated so that they are not visible. The myelin sheath, which insulates the nerve fibres, normally spreads along the optic nerve from the central nervous system and stops at the lamina cribrosa deep in the optic nerve head. Occasionally the myelination continues onto the retina so that the nerve fibres become visible as an opaque, white, striated patch with feathery edges. Very rarely this may occur as an isolated patch in another part of the retina.
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