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Central retinal artery occlusion. (A) A 62-year-old woman with a history of a previous stroke had sudden visual loss in her left eye. Her evaluation led to a diagnosis of embolic central retinal artery occlusion (CRAO). The funduscopic examination in the affected eye (pictured) shows narrowing of the retinal arterioles; pale retina, especially in the macular area; and the cherry-red spot centrally. The cream-colored edematous nerve fiber layer is most evident where the nerve fiber layer is thickest, in the macula between the vascular arcades. Because of the anatomic peculiarities of the foveola, there are no axons to obscure the normal red color of the uninvolved choroidal circulation, which stands out against the pale surrounding macula, giving rise to the infamous cherry-red spot. When the retinal edema subsides (in days to weeks), the diagnosis will not be as obvious. (B) Electroretinogram (ERG) in a Source: Unexplained Visual Loss: Anterior Segment, Retinal, and Nonorganic Disorders, Practical Neuroophthalmology patient with a CRAO. A CRAO affects the inner retina, but the photoreceptors in the outer retina are supplied by the choroid, and so their function is Citation: Martin JJ. Practical Neuroophthalmology; 2013generated Available at: 09, 2017 preserved. This is evident in TJ, theCorbett ERG pictured, with preservation of the a-wave by http://mhmedical.com/ the intact outer retina, Accessed: but loss ofJune the b-wave from ischemia Copyright © 2017 McGraw-Hill Education. All rights reserved of the inner retina. (Normal b-wave is shown for comparison; see Figure 2–28B).