Washington ? Millions of men take impotence drugs like Viagra. Now reports that 43 of them have developed a not-too-rare form of blindness have health officials examining if the drugs might play any role.

There’s no evidence yet that the drugs increase risk. Indeed, the same types of illnesses that lead to impotence are linked to this type of vision loss.

Still, “we take this seriously,” said Food and Drug Administration spokeswoman Susan Cruzan, as the agency disclosed Friday that it was talking with the makers of Viagra, Cialis and Levitra about what the labels of those drugs should say about the reports. Cialis’ maker recently, and voluntarily, added a one-line mention to its label.

At issue is sudden vision loss when blood flow to the optic nerve is blocked, a condition called NAION or nonarteritic anterior ischemic optic neuropathy.

The FDA has 43 reports of NAION among the impotence drug users. They include varying degrees of vision loss, including blindness. Those are rare numbers, given that Viagra alone has been used by 23 million men worldwide since its approval in 1998, according to maker Pfizer Inc.

Also complicating the question: NAION is considered one of the most common causes of sudden vision loss in older people, and estimates suggest there are anywhere from 1,000 to 6,000 cases a year. Risk factors include diabetes and heart disease, two of the leading causes of impotence.

But the questions come at a time when federal regulators and the drug industry are facing criticism about how they ensure the safety of drugs already on the market.