Correspondence

Medical Mystery: Cloud Surrounding the Optic Disks — The Answer

N Engl J Med 2008; 358:970-971February 28, 2008

Article

The medical mystery in the January 3 issue1 involved fundus photographs (Figure 1Figure 1Myelinated Retinal Nerve Fibers.) showing a yellow cloud surrounding the optic disks of a 42-year-old man. His visual acuity and the examination of the anterior segment of each eye were normal. The diagnosis is myelinated retinal nerve fibers, a developmental anomaly in which myelination appears beyond the lamina cribrosa or the optic nerve head, on the nerve fibers of the disk and retina. The myelinated fibers appear as striated white patches with feathery borders, caused by differential myelination of individual axons. Myelinated retinal nerve fibers occur in 1% of the population and may mimic optic-disk swelling or papilledema; an important differentiating feature is the absence of a feathery appearance in true optic-disk swelling. The occurrence is bilateral in 17 to 20% of cases and is continuous with the disk in 81% of cases. Usually, visual acuity is normal, and no particular ophthalmologic follow-up is necessary.