Sildenafil citrate inhibits phosphodiesterase type 5 and has been used to treat erectile dysfunction and pulmonary arterial hypertension.1 However, sildenafil also inhibits phosphodiesterase type 6 in retinal photoreceptors.1,2 Phosphodiesterase type 6 is known as an important component of the phototransduction cascade in the outer segments of photoreceptors regulating the ion channels.1,2 Although the affinity of sildenafil for phosphodiesterase type 6 is approximately 10% of that for phosphodiesterase type 5 , the hazards of sildenafil on human visual function should not be ignored.2 Therefore, we present the longitudinal changes over 12 months in ocular findings with electrophysiologic features of a patient who took a very high dose of sildenafil.