Using Calcium Dobesilate to Treat Chinese Patients With Mild to Moderate Non-proliferative Diabetic Retinopathy

Inclusion Criteria: * Being diagnosed with mild to moderate diabetic retinopathy * Being older than 18 years * Being willing to attend this trial. Exclusion Criteria: * Being allergic hypersensitive to experimental drugs or comparator drugs * Having alanine aminotransferase or aspartate aminotransferase ≥2 times higher than the upper limit of normal value, or total bilirubin ≥1.5 times higher than the upper limit of normal value upon the exclusion of mild fatty liver disease * Having severe renal insufficiency (defined as an estimated glomerular filtration rate ≤30 mL/min/1.73 m\^2) * Having malignant tumor and some other life-threatening diseases * Being in pregnancy, expecting pregnancy, or breast feeding * Being with unstable conditions, such as: uncontrolled high blood pressure (e.g., blood pressure \>180/100 mmHg); hemoglobin A1c \>8.0% or uncontrolled high blood glucose or hypoglycemia; acute cardiovascular events like unstable angina, congestive heart failure, stroke, transient ischemic attack, or myocardial infarction within the previous 3 months; uncontrolled infection; and diabetic ketoacidosis or hyperosmolar state in the past 1 month * Being with glaucoma, cataracts, or other opacities that may interfere with retinal examination and fundus photography * Receiving laser treatment, cryo-coagulation, or vitrectomy * Taking drugs such as diabetic retinopathy or traditional Chinese medicine that may help to improve micro-vascular function in the past 2 weeks * Receiving vascular endothelial growth factor therapy in the past 4 months or will be judged to take vascular endothelial growth factor therapy because of disease progression * Having attended other clinical trials in the past 1 month, being attending some clinical trials, or some other conditions that were judged unfit for this trial by investigators