(1) Abnormal colour vision and brightness were two adverse effects of sildenafil observed during pre-marketing studies. Both effects are dose-dependent and reversible, and led to sildenafil being contraindicated in patients with hereditary degenerative retinal disturbances such as pigmentary retinitis. (2) Several cases of anterior ischaemic optic neuropathy have been reported since the marketing release of sildenafil. These are potentially serious adverse effects that can have permanent sequelae, such as a reduced field of vision.