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Myelinated nerve fibres

Disease
Within the intracranial portion of the optic nerve, myelin sheaths are produced by oligodendrocytes and surround the nerve fibres until they reach the lamina cribrosa within the optic nerve head.

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Symptoms

The vast majority of patients are asymptomatic. Patients with extensive myelination may have an increased incidence of myopia, amblyopia and strabismus.

Signs

Myelinated nerve fibres are unilateral in 80 per cent of cases. They appear as white-yellow patches with feathery borders in the superficial retina the fibres follow the orientation of the nerve fibre layer and respect the horizontal raphe. Underlying retinal structures are often obscured from view, including the retinal vessels and the area may be totally opaque. The location and extent of myelinated nerve fibres is highly variable. The patches often extend from the optic nerve for a short distance into the retina, and occasionally continue in an arcuate path to the peripheral fundus. Patches that partially obscure the disc margin occasionally resemble papilloedema on cursory examination. Rarely, there are peripheral patches of myelination only. Variable, but usually minimal, corresponding visual field defects are common.

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