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Viagra Does Not Cause Retinal Abnormalities, Research Shows LONDON, ENGLAND -- Jan. 29, 1999 -- Can the visual symptoms that some patients taking Pfizer Inc.’s Viagra (sildenafil), a drug indicated for the treatment of erectile dysfunction, complain of be a side-effect of the drug? The retina is a sensitive network of nerve cells, fibres and photoreceptors that line the back of the eye. Sildenafil inhibits the production of a substance called phosphodiesterase (PDE) type 6. When light hits the photoreceptors in the retina, PDE type 6 is needed to transform light into electrical signals that go to the brain. Dr. Michael Vobig and colleagues from the University of Cologne, Germany, investigated whether this inhibitory effect of sildenafil had any retinal side-effects. Their results are published in this week’s issue of The Lancet. Five healthy volunteers were given a 100 mg tablet of sildenafil. Tests of retinal function were done just before the volunteers took the sildenafil and at one and six hours afterwards. The drug was found to have no effect on vision and there were no retinal abnormalities. The only effect was a reduction in retinal function one hour after sildenafil was taken, but function returned to normal within six hours. "It seems that retinal function in patients receiving sildenafil should be monitored," the researchers write. Related Links: Viagra, Pfizer Inc., The Lancet E-mail this page to a friend or colleague! To print, use this version