ONH appearance in nonarteritic anterior ischemic optic neuropathy (NAION) and arteritic anterior ischemic optic neuropathy (AAION). A, The healthy eye demonstrates a characteristic crowded appearance, which has been called “disc at risk.” B, ONH appearance in NAION. Edema is segmental, with mild superimposed pallor and flame hemorrhages. C, The healthy eye demonstrates a normal cup–disc ratio. Lack of a disc at risk should suggest an AAION. D, ONH appearance in AAION. Pallor is more pronounced.