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A. Stockman, L.T. Sharpe, A. Tufail, P.D. Kell, G. Jeffery; Viagra® Can Slow the Visual Response to Flicker and Impair Visual Sensitivity . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5356.
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As an undesirable side effect, sildenafil citrate (Viagra®) partially inhibits the phosphodiesterase enzyme, PDE6, which plays an essential role in phototransduction. PDE6 not only activates the visual transduction cascade, but also controls the speed (or integration time) of the visual response. Reports of any detrimental effects on visual performance, however, have so far been largely inconclusive or anecdotal; but this may be due to the use of insensitive and/or ill–matched visual tests. Here, we adopt standard tests sensitive to the slowing of the visual response likely to result from the inhibition of PDE6 by Viagra.
Four subjects orally ingested standard, therapeutic, 100 mg doses of Viagra. Their temporal vision was then measured using conventional psychophysical measures of sensitivity and resolution. The target and background conditions were chosen to isolate either the short–wavelength–sensitive (S–) or the long–wavelength–sensitive (L–) and/or middle–wavelength–sensitive (M–) cones.
We find that Viagra causes mild to moderate transient losses in human temporal sensitivity. All four subjects showed clear sensitivity losses when their vision was mediated by S–cones. Those subjects who showed large S–cone losses also showed comparable losses when their vision was mediated by the L– and/or M–cones. The frequency–dependent L–cone sensitivity losses caused by the inhibition of PDE6 by Viagra are consistent with an almost doubling of the time over which visual events are normally integrated (at the particular level tested, from c. 6.9 to 12.6 ms, assuming a single integration stage).
Viagra caused some transient losses in visual sensitivity in all subjects. Though it may compromise vision in the more affected individuals under some conditions, Viagra also provides a unique tool for pharmacologically investigating the role of PDE6 in human light adaptation in vivo.
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