Fourteen men reportedly have had vision loss while taking the erectile dysfunctionerectile dysfunction drug Viagra, say ophthalmologists at the University of Minnesota.
The men lost only part of their vision.
Most of the affected men had other health problems and the structure of their optic nerve (the nerve that handles vision) raised their risk of the condition.
"The number of cases is extremely small," says Howard Pomeranz, MD, PhD, who details seven of those cases in a new report.
The condition is called nonarteritic anterior ischemic optic neuropathy (NAION).
"The likelihood of this happening in an individual is pretty small.
It's a question of weighing the relative risks," Pomeranz tells WebMD.
He suggests that men taking or considering Viagra might want to check with their doctors about any risks.
Pomeranz adds that he's also heard of three similar cases with another erectile dysfunction drug,erectile dysfunction drug, Cialis.
"I don't know of any with Levitra yet," he tells WebMD.
Viagra has been used by 23 million men, says Daniel Watts, a spokesman for Pfizer, which makes Viagra.
He says that 103 clinical trials of Viagra have not had any reports of NAION.
"We would say that there does not appear to be sufficient evidence to suggest a single identifying association of these events with Viagra therapy," says Watts.
"I have no reason to doubt their statement," says Pomeranz.
Still, he says that problems not seen in clinical trials later show up after a drug has been widely used for some time.