An ischemic optic neuropathy is a damaging event that happens in the optic nerve behind the eye when the blood supply to the nerve is temporarily blocked or interrupted. Without nutrition the nerve tissue swells and becomes damaged. Sudden and severe vision darkening occurs, often affecting either the upper or lower half of the vision. IONs tend to occur in middle age. While it is impossible to predict who will have an ION, some people have a “disk at risk” … this is tight nerve insertion in the back of the eye seen during an eye exam. Something about this anatomy puts certain people at higher risk for an ION. While not a perfect metaphor, you can imagine that people who wear tight watch bands around their wrist will have more nerve damage if their arm ever swells up. There is no treatment for an ION, other than ruling out more serious conditions like temporal arteritis. The vision loss may improve with time. A new ION will often prompt a workup to look for vasculopathic risk factors like hypertension and diabetes. If the history warrants, we may also start an embolic workup to make sure the heart is beating normally (arrhythmias can cause clot formation) and a carotid ultrasound (to look for cholesterol emboli).