Although this disc is moderately swollen, it exhibits a strikingly "quiet" appearance, with no hemorrhages, exudates, or cotton wool spots. The paucity of hemorrhage in particular helps to distinguish the disc swelling that occurs in some patients with acute optic neuritis from the disc swelling associated with non-arteritic anterior ischemic optic neuropathy. Other distinguishing features include younger age of onset and the occurrence of pain in the acute stage. Multiple sclerosis is the most common cause of optic neuritis.