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Cheryl
Guttman
The effects on the choroidal vessels do not appear to be the basis for visual symptoms occurring with sildenafil treatment and are probably of no clinical relevance in healthy individuals. But they may be potentially worrisome for those at risk from adverse events of ocular haemodynamic changes, said study investigator Timothy J McCulley MD. The recently reported study [McCulley TJ, et al Ophthalmologica 2002;216:455-8] randomised nine females and four males to receive a single, supraclinical 200mg dose of sildenafil (n=7) or no drug (n=6). Ultrasonographically-determined choroidal thickness, colour vision and contrast sensitivity were evaluated at baseline and after 90 and 180 minutes. The researchers also monitored visual symptoms. Mean choroidal thickness was essentially unchanged in all of the control subjects at the follow-up assessments, whereas more variability was observed among the sildenafil-treated subjects. Some subjects experienced thinning or no change, others had thickening of up to 9% and one individual had an increase of 33%. Mean choroidal thickness in the sildenafil group was increased at both 90 and 180 minutes compared with baseline, although not significantly. However, the variance in change in choroidal thickness from baseline was significantly higher in the sildenafil against the control group at 90 minutes. “The changes in choroidal thickness we observed were consistent with the findings of a previous uncontrolled study which reported that sildenafil increases pulsatile ocular blood flow. However, taken together, these studies are only a small piece of the puzzle and in no way definitively answer the question of what the overall effect is of sildenafil on blood flow to the eye. “It appears that in healthy individuals, sildenafil is unlikely to cause changes significant enough to be worrisome. However, we cannot rule out the potential for harm in persons with underlying vascular disease and existing tenuous ocular blood flow,” Dr McCulley said. Sildenafil has the theoretical potential to affect choroidal vascular congestion via two separate and offsetting mechanisms. Acting directly on phosphodiesterase-5 (PDE5) in the smooth muscle walls of the choroidal vessels, sildenafil might facilitate smooth muscle relaxation and increase vascular congestion. However, blood flow in the choroidal vessels might also decrease secondary to sildenafil-induced peripheral vasodilation and reduced systemic blood pressure. “It is likely the variation in choroidal thickness changes we observed in the subjects treated with sildenafil can be accounted for by inter-individual variation in the effects of this drug on the vessels in and around the eye, as opposed to on the extraocular vasculature,” Dr McCulley said. Interest
in measuring the effects of sildenafil on choroidal congestion
related both to its possible relevance as a risk factor for vascular
or IOP-related adverse events, but also to investigate whether
changes in choroidal blood flow might account for sildenafil-related
visual symptoms. Timothy
J McCulley MD |
