Myelinated retinal nerve fibres loss in Leber's hereditary optic neuropathy

Abstract

Editor, A 40-year-old man presented with bilateral, rapid, painless visual loss. He had a history of right eye anisometropic amblyopia. No cigarette smoking or alcohol abuse was declared. He had two maternal uncles with similar histories of bilateral visual loss. No genetic counselling had been carried out previously. His best corrected visual acuity (VA) was counting fingers with − 8.75 D in the right eye, and 20/60 with − 1.5 D in the left eye. Fundus examination showed normal optic discs with myelinated retinal nerve fibres (MRNF) in the right eye (Fig. 1). Right fundus at first examination. Peripapillary myelinated retinal nerve fibres, particularly at the inferior temporal border. Humphrey 24–2 static visual field testing revealed bilateral central scotoma. Normal optic disc perfusion was found at fluorescein angiography. Blood biology, biochemistry and cerebral MRI were also normal. Polymerase chain reaction (PCR) studies of the patient's leucocytes revealed a homoplasmic G11-778-A mutation of mitochondrial DNA mtDNA (one of the most common mutations responsible for Leber's hereditary optic neuropathy [LHON]). A Ubiquinone® trial failed to stop bilateral visual deterioration and the scotoma size increased bilaterally. On examination 2 years later, VA was hand motion in both eyes, there was bilateral optic atrophy and the right eye MNRF had disappeared (Fig. 2). Fundi 2 years later. (A) The right fundus shows loss of myelinated retinal nerve fibres, partial loss of papillomacular bundle and optic disc atrophy. (B) The left fundus shows optic disc atrophy. (C) Red-free photograph of the right fundus shows atrophy of retinal nerve fibres and loss of myelin. Myelinated retinal nerve fibres is a benign, developmental abnormality found on routine examination in about 1% of ophthalmic patients. It can be associated with ipsilateral myopia, strabismus and amblyopia (Buys et al. 1993). It occurs when myelinization of the optic nerve (probably issued from heterotopic oligodendrocytes) continues beyond the lamina cribrosa to involve the retinal nerve fibres. It usually remains unchanged, although MNRF may disappear after damage of the retinal ganglion cells. Several causes have been reported, namely, retinal artery occlusion, diabetic retinopathy (Gentile et al. 2002), radiotherapy for choroidal melanoma (Mashayekhi et al. 2003), chronic glaucoma (Lopez Sanchez et al. 2002), optic neuritis (Sharpe & Sanders 1975), and compression of the anterior optic pathway from the inner layer (central or branch retinal artery occlusion) (Bachmann 1922; Teich 1987), to the lateral geniculate body (Gentile et al. 2002). As far as we know, loss of MNRF has not been previously reported in LHON. In this disease, the retinal ganglion cell damage is produced by intracellular mitochondrial respiratory insufficiency (Kerrison et al. 1995).