Visual short-term effects of Viagra: double-blind study in healthy young subjects.

PURPOSE: To investigate short-term visual effects of a single 100-mg dose of Viagra (sildenafil citrate) in healthy men. DESIGN: Randomized, double-blind, placebo-controlled clinical trial of drug effects on normal volunteers conducted by a single center. METHODS: Twenty men, aged 20 to 40 years, were treated with either a placebo or 100 mg sildenafil. Visual function tests included electroretinogram (ERG) recordings, on-/off- and 3.3 Hz-flicker-ERG recordings, anomaloscope matches, and measurements of cone contrast sensitivities and transient tritanopia. RESULTS: Most visual tests did not differ between the sildenafil and placebo groups. However, statistically significant increases in sensitivity during transient tritanopia were observed as well as significant prolongations in the implicit times of scotopic a-wave, photopic b-wave, and 3.3 Hz-flicker a-wave and b-wave ERG recordings. The magnitude of the differences correlated with peak sidenafil plasma concentration. Although rod amplitudes of the ERG recordings tended to be higher and cone amplitudes lower in the sildenafil group after drug ingestion, the differences were nonsignificant. There were no reports of visual side effects, and all electrophysiologic and psychophysical measurements returned to the normal range within 24 hours. CONCLUSIONS: A single oral dose of 100-mg sildenafil given to healthy young men led to small but statistically significant transient changes of outer and inner retinal function, as detected by ERG and psychophysical methods. Although the acute effects were fully reversible within 24 hours, it would be worthwhile to compare them with those induced by other PDE5 and PDE6 inhibitors.

Visual acuity and X-linked color blindness.

PURPOSE: Optimal sampling for visual acuity requires a fine array of cones with identical sensitivity. Thus, dichromats, whose inner fovea is made up of cones having the same spectral sensitivity, may have better than normal visual acuity. We investigated this by comparing the visual acuities of trichromats and X-linked dichromats, while taking into account the different molecular genetics underlying the disorder. METHODS: Our subjects were age- and refraction-matched groups of normals (n=8) and X-linked dichromats (n=13). The dichromats (four protanopes and nine deuteranopes) were genotyped and classified according to whether they carried a single (n=6) or multiple (n=7) visual pigment genes on their X-chromosome. Visual acuity was measured in both eyes with the Freiburger Visual Acuity Test. RESULTS: Normal trichromats and ungenotyped dichromats do not significantly differ in visual acuity, nor do ungenotyped protanopes and deuteranopes. However, multi-gene dichromats, who possess more than one photopigment gene in the array, all of which encode for the same long- or middle-wavelength sensitive photopigment, have significantly higher visual acuity than either normal trichromats or dichromats who have only a single-gene. CONCLUSIONS: Multi-gene dichromats may benefit from a reduction in chromatic aberration and chromatic noise in the high acuity channel, normally a consequence of combining signals from different cone photoreceptor types and of cone-specific patterns of retinal image defocus and blur. Single-gene dichromats may not share in the advantage because of other molecular differences that influence the development of the retinal mosaic and/or its visual pathways.

Dose-dependency and time-course of electrophysiologic short-term effects of VIAGRA: a case study.

The dose-dependency and time-course of the short-term visual effects of sildenafil citrate (VIAGRA) were tested in two subjects. Blood pressure was measured and samples of blood taken at 30 min intervals before and after drug administration. In the first experiment, prolongations of the implicit times of the scotopic maximum a-wave, cone a- and b-wave, 33 Hz flicker, ON-response a- and b-wave and 3.3 Hz a- and b-wave electroretinogram (ERG) recordings and of the oscillatory potentials OP1, OP2, and OP3 were observed for both eyes of both subjects, following 100 or 200 mg dosings. Interestingly, no prolongation was found for OP4, to which the OFF-bipolar cell pathway significantly contributes. In the second experiment, in which visual function was repeatedly assessed following a 200 mg dose, similar prolongations were found in both eyes of one subject for the implicit times of the oscillatory potential OP2, the cone b-wave response and the 3.3 Hz a-wave. Moreover, the steady-state (A0) and immediate extinction (B0) blue target thresholds of transient tritanopia were raised relative to the pre-drug administration baseline effects. While the maximum lowering of both systolic and diastolic blood pressure approximately correlated with the peak plasma concentration of sildenafil (c. 30-60 min after administration), the peak magnitudes of most visual effects were found at c. 110 min, consistent with a second compartment kinetic.