Calcium dobesilate has been recommended to treat diabetic retinopathy due to its potential in protecting against retinal vascular damage. However, there was limited evidence exploring its efficacy in combating diabetic retinopathy progression. This study, a single-blind, multicenter, cluster-randomized, controlled superiority trial, was designed to evaluate whether calcium dobesilate could prevent diabetic retinopathy progression into an advanced stage among Chinese patients with mild to moderate non-proliferative diabetic retinopathy.

A total of 1,200 patients with mild to moderate non-proliferative diabetic retinopathy will be enrolled and randomly assigned at a ratio of 1:1 into the control group (that is, conventional treatment group) and the intervention group (that is, conventional treatment plus calcium dobesilate [500 mg, 3 times per day] for 12 months). The severity of diabetic retinopathy will be assessed by the Early Treatment Diabetic Retinopathy Study scale.

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