In the presence of diabetic macular edema (DME), the parameters “foveal thickening” and “presence of cystoid spaces” do not thoroughly describe the disease. The evaluation of other functional parameters called “bio-markers” is necessary for therapeutic and prognostic purposes. In the presence of DME, we observe a progressive retinal damage that is functional at first stages but eventually anatomical and irreversible. The European School for Advanced Studies in Ophthalmology classification of DME describes this process for the first time via the progressive impairment of seven biomarkers. Four stages of progression are described: Early and Advanced DME represent the functional retinal impairment, while Chronic and Atrophic stages describe the evolution to anatomic and irreversible damage. The classification gives standard images for an easy and daily use, but also a comprehensive description of all optical coherence tomography images and biomarkers dedicated to retinologists and also a numerical score for scientific use in clinical trials.