Background: Interferon (IFN)-associated retinopathy is typically characterize d by retinal hemorrhages and cotton wool spots at the posterior fundus, but visu al function is usually maintained. With the use of optical coherence tomography (OCT), two patients with IFN-associated retinopathy who had developed macular e dema and reduced visual acuity during the clinical course of IFN therapy were ob served. Cases: A 37-year-old man with chronic hepatitis C and a 59-year-old man with chronic myeloid leukemia, both of whom had received IFN therapy, were r eferred to our outpatient clinic. The former patient had complained once that hi s visual acuity had decreased after the termination of IFN therapy, and the latt er patient complained twice during IFN therapy that his visual acuity had decrea sed. Observations: In both patients, at the time of the visual disturbances, mac ular edema was clearly observed by OCT. Hypoalbuminemia and thrombocytopenia wer e observed at this time also. After the remission of the hypoalbuminemia and thr ombocytopenia, the macular edema observed by OCT disappeared and visual acuity r eturned to normal. Conclusion: During and after IFN therapy, OCT is a useful exa mination technique for revealing macular edema in patients who have decreased vi sion. Ophthalmologists should be aware of the ocular side effects of IFN therapy and carefully monitor patients for the possible occurrence of hypoalbuminemia a nd thrombocytopenia. Background: Interferon (IFN) -associated retinopathy is typically characterize d by retinal hemorrhages and cotton wool spots at the posterior fundus, but visu al function is usually maintained. With the use of optical coherence tomography (OCT), two patients with IFN-associated retinopathy who had developed macular e dema and reduced visual acuity during the clinical course of IFN therapy were ob served. Cases: A 37-year-old man with chronic hepatitis C and a 59-year-old man with chronic myeloid leukemia, both of whom had received IFN therapy, were r eferred to our outpatient clinic. The former patient had complained once that hi s visual acuity been decreased after the termination of IFN therapy, and the gol er complained twice during IFN therapy that his visual acuity had decrea sed. Observations: In both patients, at the time of the visual disturbances, mac ular edema was clearly observed by OCT. After th e remission of the hypoalbuminemia and thr ombocytopenia, the macular edema observed by OCT disappeared and visual acuity r eturned to normal. Conclusion: During and after IFN therapy, OCT is a useful exa mination technique for revealing macular edema in patients who have decreased vi sion Ophthalmologists should be aware of the ocular side effects of IFN therapy and carefully monitor patients for the possible occurrence of hypoalbuminemia a nd thrombocytopenia.