The medical mystery in the January 3 issue1 involved fundusphotographs (Figure 1) showing a yellow cloud surrounding theoptic disks of a 42-year-old man. His visual acuity and theexamination of the anterior segment of each eye were normal.The diagnosis is myelinated retinal nerve fibers, a developmentalanomaly in which myelination appears beyond the lamina cribrosaor the optic nerve head, on the nerve fibers of the disk andretina. The myelinated fibers appear as striated white patcheswith feathery borders, caused by differential myelination ofindividual 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 featheryappearance in true optic-disk swelling. The occurrence is bilateralin 17 to 20% of cases and is continuous with the disk in 81%of cases. Usually, visual acuity is normal, and no particularophthalmologic follow-up is necessary.
Sandeep Randhawa, M.D. Andrew G. Lee, M.D. University of Iowa Hospitals and Clinics Iowa City, IA 52242 andrew-lee{at}uiowa.edu
Editor's note: We received 654 responses for this medical mystery,from 61 countries. Sixty-five percent of respondents were practicingphysicians, 18% were physicians in training, 10% were medicalstudents, and 7% were other readers. Fifty-eight percent correctlydiagnosed myelinated retinal nerve fibers. Other common diagnosesincluded papilledema, lipemia retinalis, glaucoma, neoplasticprocesses, multiple sclerosis, sarcoidosis, and a variety ofinfections, such as infection with cytomegalovirus, toxoplasma,or Mycobacterium tuberculosis. It is important not to confusethis benign finding on physical examination with optic-nerveedema.
References
Randhawa S, Lee AG. Medical mystery: cloud surrounding the optic disks. N Engl J Med 2008;358:69-69. [Free Full Text]
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