DR. HOWARD POMERANZ, UNIVERSITY OF MINNESOTA: Well, this patient that I just illustrate from 1998 noticed the consequence within 45 minutes after using the drug. Most of these patients practice this within hours.

GUPTA: And what Dr. Pomeranz who printed the research showing the association noticed was not total blindness, but things like loss of tangential vision or a deterioration of vision, for instance, going from 20/20 to 20/40.

The truth is, it may be complicated to ever show a link among these medications and vision troubles. That's as the same troubles that get the stroke in the back of the eye are those with high cholesterol, high blood pressure, diabetes and a history of smoking. They're as well more likely to have erectile dysfunction and take a medicine like Viagra.

BERELOWITZ: You have the similar group of patients with the same character who might be at risk for this very, very uncommon condition that have an effect on the eyes.

GUPTA: Still, if you take place to be one who in reality reads those package inserts, you won't find reference to visual loss in there. But Pfizer is talking to the FDA on the subject of whether to add it.

Still upset?

POMERANZ: Well, I consider there's some concern, but I don't believe that everyone wants to go running in panic to their doctors.

GUPTA: And definitely, if you ever had a visual trouble after taking Viagra, Levitra or Cialis discuss to your medical doctor about getting your eyes checked.

Dr. Sanjay Gupta, CNN, reports.

BROWN: Flesh out a small piece more on the science and the medicine behind the apprehension here with Viagra and the other drugs, we spoke previous tonight with Doctor Pomeranz again.

BROWN: Do you familiar with what it is about the drug that causes this difficulty when the problem is caused?