The microscopic appearance of a central retinal artery and vein are shown here. Both vessels penetrate the optic nerve posterior to the optic disc and course through the center of the optic nerve anteriorly until they enter the eye through the center of the optic nerve head prior to dividing. The central retinal artery and vein share a common adventitial sheath within the optic nerve. [Image contributed by Nick Mamalis, MD, University of Utah]

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