We report a rare case of a patient who developed age-related macular degeneration (AMD) in one eye during treatment of diabetic macular edema (DME) in both eyes. A 70-year-old man was followed for diabetic retinopathy for 23 years. At his initial visit in 200X, his decimal visual acuity was 1.0 in both eyes. He underwent panretinal photocoagulation for pre-proliferative diabetic retinopathy (PPDR) in both eyes. Optical coherence tomography (OCT), which was done nine years after the initial visit, revealed a small retinal pigment epithelial detachment (PED) in the left eye. Sixteen years after the initial visit, he developed DME in his right eye and an epiretinal membrane (ERM) in his left eye. Seventeen years after the initial visit, he developed DME in his left eye, and he was treated with sub-tenon triamcinolone acetonide (STTA) injections in the right eye. The STTA was not effective, and we switched to anti-vascular endothelial growth factor (anti-VEGF) injections for both eyes. The anti-VEGF injections were performed 22 times (aflibercept, IVA 12 times
faricimab, IVF 10 times) in the right eye for the DME. His decimal visual acuity fluctuated between 0.2 and 0.9 during this period. The left eye underwent pars plana vitrectomy (PPV) for the DME and ERM 17 years after the initial visit. Although the macular edema was resolved, subretinal fluid and macular neovascularization (MNV) appeared 22 years after the initial visit. Since then, IVF has been performed 10 times, and the decimal visual acuity has improved from 0.4 to 0.8. He underwent bilateral cataract surgery 17 years after the initial visit. Twenty-two years after the initial visit, the left eye developed MNV, located near the PED that had been seen on the OCT image taken 13 years earlier. The relationships of the ERM, DME, and PPV with MNV were not determined. At present, both eyes are responding well to the IVF treatments. This case will remind clinicians of the possibility of the two diseases coexisting and will lead to a better understanding of the pathogenic mechanisms of both diseases.