Answering concern about reports of a rare form of sudden blindness afflicting men who had taken erectile dysfunction medications Viagra, Cialis, and Levitra, the Food and Drug Administration issued a warning label to adorn all new packaging. The particular form of blindness, non-arteritic anterior ischemic optic neuropathy (NAION), is caused by lack of blood flow to the optic nerve and is most common in the elderly, especially among those suffering from diabetes or high blood pressure. The condition affects an estimated 1,000 to 6,000 Americans a year. After 38 Viagra users reported sudden vision impairment soon after taking the drug,...