NAION, or Non-Arteritic Anterior Ischemic Optic Neuropathy, is a condition that affects the optic nerve, leading to sudden vision loss in one eye. It occurs when blood flow to the optic nerve is reduced, often due to small vessel disease. Risk factors include age, hypertension, diabetes, and sleep apnea. Symptoms typically include a sudden decrease in vision, often described as a "darkening" or "graying" of vision. Diagnosis is usually made through a clinical examination and imaging tests. While there is no specific treatment for NAION, managing underlying health conditions may help reduce the risk of further episodes.