Ischemic optic neuropathy and optic neuritis are the most common causes of unilateral non-glaucomatous visual loss. While they have distinctive clinical features, they also share some overlapping profiles that make it difficult to clinically distinguish these two entities. MRI with gadolinium has been proven to be helpful to confirm the diagnosis of optic neuritis, but ischemic optic neuropathy remains a clinical diagnosis. Diffusion MRI, a newly advanced technique, has been used in studying the pathophysiology of optic neuritis, but its use in ischemic optic neuropathy is limited. Diffuse MRI may potentially be of help to diagnose ischemic optic neuropathy.