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The appearance of myelinated nerve fibres within the fundus results from the anomalous myelination of nerve fibres anterior to the lamina cribrosa. Structural change is confined to the nerve fibre layer of the retina. The myelin sheaths may be produced by ectopic oligodendrocytes, or by intraretinal Schwann cells. (The latter occurs in the normal retina of the cat and rat.)
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.
Prevalence
Common - present in approximately 1 per cent of the population.
Significance
Typically benign and stable.
Differential diagnosis
Cotton wool spots, Astrocytic hamartomas, Commotio retinae, Papilloedema.
See also
Optic neuritis.
Management
Additional investigations
Routine visual field testing may be indicated if the myelination is extensive.
Advice
No treatment is required. Lesions have rarely been reported to disappear in patients following optic neuritis or in demyelination disease.