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When Viagra was introduced in 1999, the drug's manufacturer warned of a number of side effects, including possible nerve damage to the eyes. But a UC Irvine College of Medicine study rules out some of these risks—even when the drug is taken in high doses.

According to Dr. Tim McCulley, assistant professor of ophthalmology, blood flow in the eye does not seem to be reduced by even high doses of the popular erectile dysfunction drug. Since Viagra lowers blood pressure overall, there was persistent suspicion that the drug might cause decreased optical blood flow, which can cause nerve damage.

McCulley's study appears in the January 2003 issue of Ophthalmologica.

"Viagra can change blood vessel structure as well as general blood pressure, so we needed to answer the question whether the drug could change blood vessels in the eye," McCulley said. "Our study may have had a small group of participants, but it showed very little change in blood vessels or blood flow in nearly all the patients."

McCulley's team conducted the trial with 13 men at Stanford University and found that high doses of Viagra by and large preserved the thickness of the eye's choroids layer, which supplies the eyeball with blood. However, the team did find some small variations in thickness, which indicated that some people with underlying vascular diseases may indeed have changes in vision.

In addition, the researchers found no connection among blood flow choroid thickness and changes in color vision, a common side effect of taking Viagra, or sildenafil citrate.

McCulley's team confirmed these side effects, finding that Viagra users had a harder time discriminating among subtle changes in color. But they also found that Viagra users reported problems in picking out any number of colors, not just the blue-green variety reported during the drug's clinical trials.

Source: University Of California at Irvine