Myelinated retinal nerve fibres are fairly common developmental abnormalities and are benign in most cases. We would like to report an unusual case of bilateral macula atrophy and papillomacular myelinated nerve fibre associated with poor vision.
A 9-year-old girl who recently moved from Germany was referred by her opticians for changes in the appearance of her fundi. There, she was treated with glasses and patching but told that visual prognosis was limited due to retinal changes. There was no family history of ophthalmic problems. Other than a recent stress fracture, she was healthy.
On refraction, her prescription was Right (R) −3.50/+2.00 × 5 and Left (L) −4.50/−1.00 × 180. Her corrected visual acuity was R 6/24 and L 6/60. Orthoptic examination revealed a left convergent squint with latent nystagmus. Anterior segment examination was unremarkable. Fundus examination revealed bilateral macular atrophy with bilateral papillomacular bundle myelinated retinal nerve fibres (see Fig. 1). Despite correction of refractive error and amblyopic treatment, her vision remained poor. She was registered partially sighted and referred to the Advisory Teacher for Visually Impaired Children.
In normal prenatal development, myelination of the optic nerve begins at the lateral geniculate body and progresses towards the eye. This process terminates posterior to the lamina cribrosa before birth. However, occasionally this process extends further anteriorly along the nerve fibres of the optic nerve head and the sensory retina. Myelinated retinal nerve fibres are reported in up to 0.3–0.98% of patients and maybe bilateral in up to 7.7–20% of affected individuals.1,2
Myelinated nerve fibre lesions appear as white or grey-white striated patches corresponding in shape to the distribution of retinal nerve fibres with frayed borders. By light microscopy and electron microscopy, myelinated retinal fibres are marked by a ganglion cell axon surrounded by concentric lipoprotein lamellae that forms the myelin sheath. Glial cells are often prominent near the myelin sheaths, but other components of the sensory retina are morphologically normal.1 The appearance of the myelinated retinal nerve fibres tends to stay unchanged. However, with fibre destruction and optic atrophy, myelination can slowly disappear (e.g. in multiple sclerosis, pituitary tumours and embolism of the central retinal artery).3
Myelinated nerve fibres have been linked to numerous ocular abnormalities including craniofacial abnormalities, neurofibromatosis, coloboma, polycoria and keratoconus.2 An important association as well is papillary myelinated nerve fibres with anisometropic myopia, strabismus and decreased vision.4,5 Myopia is more common in widespread myelinated nerve fibres compared to circumscribed myelinated nerve fibres.6 The origin of this association is unknown but these patients are somewhat refractory to amblyopia therapy. These patients are somewhat refractory to amblyopia therapy.1,4,5 Despite the poor prognosis, the clinician should perform cyclopaedic refraction when extensive peripapillary myelinated retinal nerve fibres are found. Patients and their families should be given appropriate counselling as prognosis is often guarded.
Possible causes of bilateral macular atrophy include central areolar choroidal dystrophy, Stargardt's disease, North Carolina macular dystrophy and cone dystrophy. The lack of family history and normal electroretinography (both pattern and flash) and electrooculography make the above differential unlikely. As far as we are aware, this is the first reported case of bilateral papillomacular myelinated retinal nerve fibre associated with bilateral macular atrophy and bilateral myopia. The changes in our patient's fundus appear symmetrical. Our patient has anisometropic myopia being more myopic in the left. She has poor vision in both eyes secondary to macula atrophy. However, vision in the left eye is poorer probably as a result of the anisometropia. Despite our efforts, her prognosis remains limited.