Myelination of the optic nerve fibers normally begins at the lateral geniculate body and ceases at the lamina cribrosa
An abnormal intraocular myelination of the peripapillary nerve fibre layer anterior to the lamina cribrosa is called myelinated nerve fibre layer (MNFL)
Usually unilateral - can be sporadic/ familial/ acquired
Oligodendrocytes are involved- a structural or biochemical defect allows oligodendrocytes to migrate intraocularly and continue myelination past the lamina cribrosa
White, well-demarcated, feathery edges
Run in arcuate bundles
Continuous with the optic disc
Obscures the underlying retinal vessels
Visually insignificant, usually
Visual field defects : enlargement of blind spot, mild arcuate scotomas
Associations - myopia, amblyopia, ansiometropia, strabismus, drusen of optic nerve etc.
Syndromes: Down’s, Gorlin- Gortz, NF Type 1 etc
In optic neuritis caused by multiple sclerosis, a demyelinating condition, MNFL can disappear. They can also disappear in neurological conditions such as pituitary adenoma, inflammatory conditions such as Behcet’s after recurrent papillitis and vitritis, and retinal diseases such as arterial occlusions, diabetic retinopathy, vitrectomy etc.