10 This imbalance is believed to be more likely to occur in myopia, due to the enlarged eyeball. 4, 10 It has been postulated that MRNF results from an imbalance between the formation of the lamina cribosa, which proceeds posteriorly from the limbus and the process of myelination, which begins from the lateral geniculate body. Oligodendrocytes are responsible for the myelination of the ganglion cell axons, which normally begins at the lateral geniculate body and proceeds anteriorly to end at the lamina cribosa, which is thought to act as a barrier to the anterior migration of myelination into the retinal nerve fibres. The exact pathogenesis of MRNF is not known. 7, 8 Other ocular and systemic associations with MRNF include epiretinal membrane, branch retinal artery occlusion, branch retinal vein occlusion, neovascularisation, recurrent vitreous haemorrhage, keratoconus, neurofibromatosis 1 and Gorlin's syndrome. 3, 4, 5, 6 The patient, therefore, has a syndrome of ipsilateral myelinated retinal nerve fibres, anisometropic myopia, amblyopia and strabismus.Īlthough, MRNF is known to be associated with myopia, rare cases of MRNF associated with hypermetropia and amblyopia have been documented. There may also be associated misalignment of the visual axes of the eyes referred to as strabismus (squint), in which there may be an outward deviation of the eye (exotropia) or an inward deviation (esotropia). The myopia may be unresponsive to optical correction with lenses (that is the vision cannot be improved with optical correction), in which case the patient is referred to as having amblyopia. This is referred to as anisometropic myopia. 4 The patient may have myopia in the eye with MNRF, and emmetropia (no refractive error) or myopia of a lesser degree in the fellow eye. In majority of cases, the patient's vision is not affected however, some cases have been associated with the refractive error, myopia, which causes poor vision. They obscure the retinal blood vessels and the disc. They are recognised on fundoscopy as grey-white opaque patches on the retina with striations and feathery edges, which usually give away the diagnosis. Myelinated retinal nerve fibres are diagnosable clinically. In the normal eye, the retinal nerve fibre layer is transparent and unmyelinated, allowing visualisation of the retinal blood vessels. There was no improvement in vision with optical correction in the left eye suggesting amblyopia. Refraction revealed emmetropia in the right eye and −18.75 −1.75 × 153° in the left eye. The axial lengths were 23.6mm and 28.7mmm in the right and left eye respectively. In the left eye, there was extensive MRNF extending from the disc along the superotemporal arcade up to the midperiphery, sparing the macula. On dilated fundoscopy, the right eye had a normal disc with a cup to disc ratio of 0.3, and normal retina. Intraocular pressure was 10mmHg by applanation tonometry in either eye.
MYELINATED RETINAL NERVE FIBER LAYER FULL
The left eye had an exotropia of 15° with full ocular motility, normal anterior segment and a subtle relative afferent pupillary defect. Unaided visual acuity was 6/5 right eye and counting fingers at 1metre in the left eye. She had no other ocular symptoms, but had a history of absence seizures. A 22-year-old Nigerian female student was referred to us on account of poor vision in the left eye, first noticed incidentally 12 years ago, on closing the right eye.
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