Ischemia from the closure of ciliary vessels that supply the optic nerve can also lead to visual loss, a condition called ischemic optic neuropathy, shown in the slide as slight blurring of the optic nerve margins. Typically, patients report some visual loss; it may be severe (a central scotoma) or may be demonstrated only on visual field testing. Color perception, when tested, will be diminished in the eye with ischemic optic neuropathy. Ischemic optic neuropathy may be arteritic (associated with temporal arteritis) or non-arteritic. When ischemic optic neuropathy is non- arteritic, the optic nerve usually is small. Swelling of the optic nerve may obscure the ability to determine if the nerve is small, but the fellow eye can be examined for this possibility since the size of the optic nerves usually are fairly symmetric. Because of the risk of severe vision loss from arteritic ischemic optic neuropathy, patients older than 50 diagnosed with ischemic optic neuropathy should have a sedimentation rate and C-reactive protein level checked urgently to rule out temporal arteritis.