AARON BROWN, CNN ANCHOR: Good evening once again. If you've ever seen a direction medication commercial, in other terms, if your television works at all, you've gotten to be aware of the fast talking man, the one that tells you about the weakness, fainting spells and dry mouth. At the present time the Food and Drug Administration said it requirements to give him one other thing to mention maybe. It is asking the creator of Viagra to keep knowledgeable its warning label to indicate vision loss.

So far the numbers are little and the connection not completely explored, but given how many public who use Viagra and drugs like it to treat weakness of just for the thrill, nobody's taking any probability. So, we start tonight with Dr. Sanjay Gupta.

DR. SANJAY GUPTA, CNN SENIOR MEDICINALCORRESPONDENT (voice-over): The concern isn't latest. It has been recognized for years that users of Viagra could familiarity short term vision changes, seeing green or bluish hues.

MICHAEL BERELOWITZ, VP WORLDWIDE MEDICAL, and PFIZER: The earliest reports we were attentive of was in 2000. More cases were published in the text in March of this year.

GUPTA: The numbers are small, extremely small; only 38 Viagra users of the in excess of 20 million who take it have come forward with vision troubles. There have also been four users of Cialis and one with Levitra with related problems, the pills manufacturers say.

They say the vision failure is caused by a sort of stroke disturbing the blood vessels of the eye. That stroke in the back of the eye occurs when the blood vessels become choked off, ultimately causing some of the cells in the eye to die.

Amusingly, the number of people who find the same type of stroke is in fact about four times advanced for people who don't take Viagra, the study's researchers say. But it's the association of timing between somebody taking the drug and then within a short time getting visual troubles that raised the red flags.