Sildenafil is a potent phosphodiesterase (PDE) 5 inhibitor that is used for patients with erectile dysfunction. Sildenafil induces vasodilation in selected smooth muscle via increased levels of guanosine 3', 5' cyclic monophosphate and increase in nitric oxide. The vasodilatory effects of the PDE 5 inhibitors led us to review its effect on the ocular vasculature. Sildenafil appears to increase blood flow velocity significantly in the retrobulbar and choroidal circulation. Most studies suggest an increase in choroidal blood flow, with a lesser effect on the retinal vasculature.