Viagra may have short-term eye effects
Monday February 1 6:40 PM ET
NEW YORK, Feb 01 (Reuters Health) -- Healthy volunteers who took a singe dose of sildenafil (Viagra) showed changes in retinal function on sophisticated testing one hour after the medication was taken, but these changes disappeared within 6 hours, according to a German study.
The researchers noted that none of the volunteers complained of visual disturbances after taking the drug.
But as a result of the findings, Dr. Michael Vobig of the University of Cologne, Germany, and colleagues suggest in a research letter published in the January 30th issue of The Lancet that ''retinal function in patients receiving sildenafil should be monitored.''
In the study, five volunteers, who were given 100 milligrams of sildenafil had their visual function tested one hour before taking the medication, an hour after taking it, and 6 hours later. In addition, concentrations of sildenafil in the blood were measured 1, 3 and 6 hours after the dose.
The tests showed no change in the clarity or range of the men's vision, and no changes in their color vision or in their intraocular pressure.
But the researchers did find that electroretinogram tests showed a slight loss in light sensitivity an hour after taking the drug. This corresponded with blood tests that found the highest concentration of the drug in blood drawn one hour after the drug was taken.
Several hours later, the results of this test were again normal. The team write that this effect of Viagra on the retina may be due to the drug's inhibition of an enzyme found in the retina called phosphodiesterase type 6, which helps to translate light hitting the retina into electrical signals that travel to the brain.
Based on their study results, Vobig and colleagues suggest that retinal function in patients receiving sildenafil should be monitored, especially in older patients or those with pre-existing abnormalities and retinal disease.
In an editorial, Dr. Eberhart Zrenner of Germany's University Eye Hospital in Tubingen writes that these study findings are ''not alarming'' in healthy patients with normal retinas. He notes that the effect of Viagra on the retina demonstrated in the study indicates ''only a very weak loss in light sensitivity... similar to the light-absorbing effect of a car windshield.''
Nevertheless he suggests more ''extensive and carefully controlled studies'' would clarify the effects of sildenafil on retinal function.
SOURCE: The Lancet 1999;353:340-341, 375.
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