Anterior ischemic optic neuropathy. Fluorescein angiogram of the retina of the right eye of a patient with anterior ischemic optic neuropathy (AION). This is a sudden loss of vision caused by insufficient blood flow to the front (anterior) of the optic nerve. It typically occurs upon waking. The condition may be caused by inflammation of the arteries supplying the nerve (arteritic-AION) or be a symptom of another cardiovascular disease such as high blood pressure, diabetes or high cholesterol (nonarteritic-AION). Treatment is of the underlying cause and may restore some vision, depending on how much damage the nerve sustained.