Contributor: Gordon K. Klintworth
NAION (nonarteritic anterior ischemic optic neuropathy) is one variety of  ischemic optic neuropathy [optic neuropathy - ischemic]. This optic neuropathy  has a rapid onset and is the most frequent cause of acute optic neuropathy [optic neuropathy - acute] in persons >60 years old. Although vascular disease is responsible for some cases, such as those with CADASIL, the clinical evidence for vascular disease in most cases is weak. The annual incidence in the USA is 3.25 /100,000 population. The condition is typically unilateral and affects elderly patients with risk factors for vascular diseases, such as hypertension and diabetes mellitus. Noncturnal hypotension may also be associated. A congenital anomaly of the optic disc is a risk factor for optic disc infarction. Males and females are affected equally. The affected optic nerve is swollen and the contralateral optic disc is usually crowded with a small optic cup. There is a higher frequency of the condition in caucasians than in African-Americans or Hispanics.