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Myelinated retinal nerve fibres usually remain unchanged but loss of myelin can occur either from primary demyelination (for example, optic neuritis) or secondary to retinal ganglion cell damage. We present a case of extensive loss of myelinated retinal nerve fibres as a result of progressive diabetic retinopathy. To our knowledge, this is a rare observation.
A 64 year old African-American woman with diabetes mellitus for 11 years, hypertension for 5 years, and hypercholesterolaemia presented, after being lost to follow up, with progressive blurred vision in both eyes. There was no history of glaucoma, laser treatment, or any other significant medical or neurological disease. Visual acuity was counting fingers in the right eye and 20/400 in the left eye. The pupillary examination, gonioscopy, and applanation tonometry were normal. A moderate nuclear sclerosis was present. Funduscopic examination revealed severe proliferative diabetic retinopathy with vitreous haemorrhages in both eyes. The left eye had peripapillary myelinated retinal nerve fibres (Fig 1) with partially cicatricial retinal neovascularisation and low lying traction retinal detachments along the superotemporal and inferotemporal arcades. There was diffuse macular oedema with cystoid changes. Fundus photographs taken 6 years earlier revealed severe non-proliferative diabetic retinopathy with macular oedema in both eyes and much more extensive peripapillary myelinated nerve fibres of the left eye (Fig 2).
The area of myelinated retinal nerve fibres had markedly decreased allowing visualisation of the previously obscured retinal vessels and optic disc margin. The loss of myelinated retinal nerve fibres was more pronounced at the superior and inferior disc margins corresponding to the areas of tractional retinal detachment.
Myelinated retinal nerve fibres are usually benign, developmental abnormalities found on routine examination. They occur when myelinisation of the optic nerve continues beyond the lamina cribrosa to involve the retinal nerve fibres. On funduscopy, they typically appear as a solitary white or grey-white striated patch which follows the nerve fibre layer. In a series of 3968 consecutive necropsies the incidence of myelinated retinal nerve fibres was found to be 0.98%.1
Myelinated retinal nerve fibres usually remain unchanged. Loss of myelin can occur either from primary demyelination—for example, in optic neuritis2 or secondary to retinal ganglion cell damage. The latter can be caused by ischaemia, inflammation, degeneration, or compression anywhere along the path of the retinal ganglion cell from the inner retinal layer to the lateral geniculate body. Reported examples involving inner retinal ischaemia as a cause of myelinated retinal nerve fibre loss include branch retinal artery occlusion3 and central retinal artery occlusion.4 In diabetic retinopathy, ischaemic changes occur in the inner retina, leading to damage to the ganglion cell and atrophy of the nerve fibre layer. This is the mechanism responsible for the loss of myelinated retinal nerve fibres in our patient. Tractional retinal detachment, usually a late complication of diabetic retinopathy, most likely contributed to the atrophy. Ischaemic damage to the retinal nerve fibres is common in early diabetic retinopathy. Chihara et al,5 using retinal nerve fibre layer photographs, found retinal nerve fibre layer defects to be common in eyes with diabetic retinopathy. We report the observation that inner retinal ischaemia secondary to diabetic retinopathy can result in the loss of myelin in the of myelinated retinal nerve fibres.