Non-arteritic anterior ischemic optic neuropathy (NAION) 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 of NAION typically include a sudden decrease in vision, often described as a "darkening" or "shadow" in the visual field. Unlike other types of optic neuropathy, NAION is not associated with inflammation of the arteries, which distinguishes it from arteritic forms. Early diagnosis and management are crucial for preserving vision.